OPSEC M. Kaeo Internet-Draft Double Shot Security, Inc. Expires: January 18, 2006 July 17, 2005 Operational Security Current Practices draft-ietf-opsec-current-practices-02 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 18, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document is a survey of the current practices used in today's large ISP operational networks to secure layer 2 and layer 3 infrastructure devices. The information listed here is the result of information gathered from people directly responsible for defining and implementing secure infrastructures in Internet Service Provider environments. Kaeo Expires January 18, 2006 [Page 1] Internet-Draft OPSEC Practices July 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Threat Model . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Attack Sources . . . . . . . . . . . . . . . . . . . . . . 4 1.4. Operational Security Impact from Threats . . . . . . . . . 5 1.5. Document Layout . . . . . . . . . . . . . . . . . . . . . 7 1.6. Definitions . . . . . . . . . . . . . . . . . . . . . . . 7 2. Protected Operational Functions . . . . . . . . . . . . . . . 9 2.1. Device Physical Access . . . . . . . . . . . . . . . . . . 9 2.2. Device In-Band Management . . . . . . . . . . . . . . . . 11 2.3. Device Out-of-Band Management . . . . . . . . . . . . . . 15 2.4. Data Path . . . . . . . . . . . . . . . . . . . . . . . . 19 2.5. Routing Control Plane . . . . . . . . . . . . . . . . . . 21 2.6. Software Upgrades and Configuration Integrity / Validation . . . . . . . . . . . . . . . . . . . . . . . . 25 2.7. Logging Considerations . . . . . . . . . . . . . . . . . . 28 2.8. Filtering Considerations . . . . . . . . . . . . . . . . . 31 2.9. Denial of Service Tracking / Tracing . . . . . . . . . . . 32 3. Security Considerations . . . . . . . . . . . . . . . . . . . 34 4. Normative References . . . . . . . . . . . . . . . . . . . . . 34 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 35 Appendix B. Protocol Specific Attacks . . . . . . . . . . . . . . 36 B.1. Layer 2 Attacks . . . . . . . . . . . . . . . . . . . . . 36 B.2. IPv4 Attacks . . . . . . . . . . . . . . . . . . . . . . . 36 B.3. IPv6 Attacks . . . . . . . . . . . . . . . . . . . . . . . 37 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 38 Intellectual Property and Copyright Statements . . . . . . . . . . 39 Kaeo Expires January 18, 2006 [Page 2] Internet-Draft OPSEC Practices July 2005 1. Introduction Security practices are well understood by the network operators who have for many years gone through the growing pains of securing their network infrastructures. However, there does not exist a written document that enumerates these security practices. Network attacks are continually increasing and although it is not necessarily the role of an ISP to act as the Internet police, each ISP has to ensure that certain security practices are followed to ensure that their network is operationally available for their customers. This document is the result of a survey conducted to find out what current security practices are being deployed to secure network infrastructures. 1.1. Scope The scope for this survey is restricted to security practices that mitigate exposure to risks with the potential to adversely impact network availability and reliability. Securing the actual data traffic is outside the scope of the conducted survey. This document focuses solely on documenting currently deployed security mechanisms for layer 2 and layer 3 network infrastructure devices. Although primarily focused on IPv4, many of the same practices can apply to IPv6 networks. Both IPv4 and IPv6 network infrastructures are taken into account in this survey. 1.2. Threat Model A threat is a potential for a security violation, which exists when there is a circumstance, capability, action, or event that could breach security and cause harm [RFC2828].Every operational network is subject to a multitude of threat actions, or attacks, i.e. an assault on system security that derives from an intelligent act that is a deliberate attempt to evade security services and violate the security policy of a system [RFC2828]. All of the threats in any network infrastructure is an instantiation or combination of the following: Reconnaissance: An attack whereby information is gathered to ascertain the network topology or specific device information which can be further used to exploit known vulnerabilities Man-In-The-Middle: An attack where a malicious user impersonates either the sender or recipient of a communication stream. Protocol Vulnerability Exploitation: An attack which takes advantage of known protocol deficiencies to cause inappropriate behavior. Kaeo Expires January 18, 2006 [Page 3] Internet-Draft OPSEC Practices July 2005 Message Insertion: This can be a valid message (which could be a reply attack,, which is a scenario where a message is captured and resent at later time). A message can also be inserted with any of the fields in the message being OspoofedO, such as IP addresses, port numbers, header fields or even packet content. Flooding is also part of this threat instantiation. Message Diversion/Deletion: An attack where legitimate messages are removed before they can reach the desired recipient or are re- directed to a network segment that is normally not part of the data path. Message Modification: This is a subset of a message insertion attack where a previous message has been captured and modified before being retransmitted. The message can be captured by using a man-in-the- middle attack or message diversion. Note that sometimes Denial of service attacks are listed as separate categories. A denial of service is a consequence of an attack and can be the result of too much traffic (i.e. flooding), or exploting protocol expoitation or inserting/deleting/diverting/midifying messages. 1.3. Attack Sources These attacks can be sourced in a variety of ways: Active vs passive attacks An active attack involves writing data to the network. It is common practice in active attacks to disguise one's address and conceal the identity of the traffic sender. A passive attack involves only reading information off the network. This is possible if the attacker has control of a host in the communications path between two victim machines or has compromised the routing infrastructure to specifically arrange that traffic pass through a compromised machine. In general, the goal of a passive attack is to obtain information that the sender and receiver would prefer to remain private. [RFC3552] On-path vs off-path attacks In order for a datagram to be transmitted from one host to another, it generally must traverse some set of intermediate links and routers. Such routers are naturally able to read, modify, or remove any datagram transmitted along that path. This makes it Kaeo Expires January 18, 2006 [Page 4] Internet-Draft OPSEC Practices July 2005 much easier to mount a wide variety of attacks if you are on-path. Off-path hosts can transmit arbitrary datagrams that appear to come from any hosts but cannot necessarily receive datagrams intended for other hosts. Thus, if an attack depends on being able to receive data, off-path hosts must first subvert the topology in order to place themselves on-path. This is by no means impossible but is not necessarily trivial. [RFC3552] Insider or outsider attacks An "insider attack" is one which is initiated from inside a given security perimeter, by an entity that is authorized to access system resources but uses them in a way not approved by those who granted the authorization. An "outside attack" is initiated from outside the perimeter, by an unauthorized or illegitimate user of the system. Deliberate attacks vs unintentional events A deliberate attack is one where a miscreant intentionally performs an assault on system security. However, there are also instances where unintentional events cause the same harm yet are performed without malice in mind. Configuration errors and software bugs can be as devastating to network availability as any deliberate attack on the network infrastructure. The attack source can be a combination of any of the above, all of which need to be considered when trying to ascertain what impact any attack can have on the availability and reliability of the network. It is nearly impossible to stop insider attacks or unintentional events. However, if appropriate monitoring mechanisms are in place, these attacks can be as easily detected and mitigated as with any other attack source. Any of the specific attacks discussed further in this document will elaborate on attacks which are sourced by an "outsider" and are deliberate attacks. Some further elaboration will be given to the feasibility of passive vs active and on-path vs off- path attacks to show the motivation behind deploying certain security features. 1.4. Operational Security Impact from Threats The main concern for any of the potential attack scenarios is the impact and harm it can cause to the network infrastructure. The threat consequences are the security violations which results from a threat action, i.e. an attack. These are typically classified as follows: Kaeo Expires January 18, 2006 [Page 5] Internet-Draft OPSEC Practices July 2005 (Unauthorized) Disclosure A circumstance or event whereby an entity gains access to data for which the entity is not authorized. Deception A circumstance or event that may result in an authorized entity receiving false data and believing it to be true. Disruption A circumstance or event that interrupts or prevents the correct operation of system services and functions. A broad variety of attacks, collectively called denial of service attacks, threaten the availability of systems and bandwidth to legitimate users. Many such attacks are designed to consume machine resources, making it difficult or impossible to serve legitimate users. Other attacks cause the target machine to crash, completely denying service to users. Usurpation A circumstance or event that results in control of system services or functions by an unauthorized entity. Most network infrastructure systems are only intended to be completely accessible to certain authorized individuals. Should an unauthorized person gain access to critical layer 2 / layer 3 infrastructure devices or services, they could cause great harm to the reliability and availability of the network. A complete description of threat actions that can cause these threat consequences can be found in [RFC2828]. Typically, a number of different network attacks are used in combination to cause one or more of the above mentioned threat consequences. An example would be a malicious user who has the capability to eavesdrop on traffic. First, he may listen in on traffic for a while to do some reconnaissance work and ascertain which IP addresses belonged to specific devices such as routers. Were this miscreant to obtain information such as a router password sent in cleartext, he can then proceed to compromise the actual router. From there, the miscreant can launch various active attacks such as sending bogus routing updates to redirect traffic or capture additional traffic to compromise other network devices. Kaeo Expires January 18, 2006 [Page 6] Internet-Draft OPSEC Practices July 2005 1.5. Document Layout This document is a survey of current operational practices that mitigate the risk of being susceptible to any threat actions. As such, the main focus is on the currently deployed security practices used to detect and/or mitigate attacks. The top-level categories in this document are based on operational functions for ISPs and generally relate to what is to be protected. This is followed by a description of which attacks are possible and the security practices currently deployed which will provide the necessary security services to help mitigate these attacks. These security services are classified as: o User Authentication o User Authorization o Data Origin Authentication o Access Control o Data Integrity o Data Confidentiality o Auditing / Logging o DoS Mitigation In many instances, a specific protocol currently deployed will offer a combination of these services. For example, AAA can offer user authentication, user authorization and audit / logging services while SSH can provide data origin authentication, data integrity and data confidentiality. The services offered are more important than the actual protocol used. Each section ends with an additional considerations section which explains why specific protocols may or may not be used and also gives some information regarding capabilities which are not possible today due to bugs or lack of ease of use. 1.6. Definitions RFC 2119 Keywords Kaeo Expires January 18, 2006 [Page 7] Internet-Draft OPSEC Practices July 2005 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. The use of the RFC 2119 keywords is an attempt, by the editor, to assign the correct requirement levels ("MUST", "SHOULD", "MAY"...). It must be noted that different organizations, operational environments, policies and legal environments will generate different requirement levels. Kaeo Expires January 18, 2006 [Page 8] Internet-Draft OPSEC Practices July 2005 2. Protected Operational Functions 2.1. Device Physical Access Device physical access pertains to protecting the physical location of the layer 2 or layer 3 network infrastructure device. Although it is important to have contingency plans for natural disasters such as earthquakes and floods which can cause damage to networking devices, this is out-of-scope for this document. Here we concern ourselves with protecting access to the physical location and how a device can be further protected from unauthorized access if the physical location has been compromised, i.e protecting the console access. 2.1.1. Threats / Attacks If any intruder gets physical access to a layer 2 or layer 3 device, the entire network infrastructure can be under the control of the intruder. At a minimum, the intruder can take the compromised device out-of-service, causing network disruption, the extent of which depends on the network topology. A worse scenario is where the intruder can use this device to crack the console password and have complete control of the device, perhaps without anyone detecting such a compromise, or to attach another network device onto a port and siphon off data with which the intruder can ascertain the network topology and take control of the entire network. The threat of gaining physical access can be realized in a variety of ways even if critical devices are under high-security. There still occur cases where attackers have impersonated maintenance workers to gain physical access to critical devices that have caused major outages and privacy compromises. Insider attacks from authorized personnel also pose a real threat and must be adequately recognized and dealt with. 2.1.2. Security Practices For physical device security, equipment is kept in highly restrictive environments. Only authorized users with card key badges have access to any of the physical locations that contain critical network infrastructure devices. These card-key systems keep track of who accessed which location and at what time. All console access is always password protected and the login time is set to time out after a specified amount of inactivity - typically between 3-10 minutes. Individual users are authentication to get basic access. For privileged (i.e. enable) access, a second authentication step needs to be completed. Typically all console access is provided via an out-of-band (OOB) management infrastructure Kaeo Expires January 18, 2006 [Page 9] Internet-Draft OPSEC Practices July 2005 which is discussed in the section on OOB management. 2.1.3. Security Services The following security services are offered through the use of the practices described in the previous section: o User Authentication - All individuals who have access to the physical facility are authenticated. Console access is authenticated. o User Authorization - An authenticated individual has implicit authorization to perform commands on the device. Console access is usually granted via at least two privilege levels: authorization for performing a basic set of commands vs authorization for performing all commands. o Data Origin Authentication - Not applicable o Access Control - Not applicable o Data Integrity - Not applicable o Data Confidentiality - Not applicable o Auditing / Logging - All access to the physical locations of the infrastructure equipment is logged via electronic card-key systems. All console access is logged (refer to the OOB management section for more details) o DoS Mitigation - Not applicable 2.1.4. Additional Considerations Physical security is relevant to operational security practices as described in this document mostly from a console access perspective. Most ISPs provide console access via an OOB management infrastructure which is discussed in the OOB management section of this document. The physical and logical authentication and logging systems should be run independently of each other and reside in different physical locations. Social engineering plays a big role in many physical access compromises. Most ISPs have set up training classes and awareness programs to educate company personnel to deny physical access to people who are not properly authenticated or authorized to have Kaeo Expires January 18, 2006 [Page 10] Internet-Draft OPSEC Practices July 2005 physical access to critical infrastructure devices. 2.2. Device In-Band Management In-band management is generally considered to be device access where the control traffic takes the same data path as the data which traverses the network. In many environments, device management for layer 2 and layer 3 infrastructure devices is deployed as part of an out-of-band management infrastructure although there are some instances where it is deployed in-band as well. Presently, the mechanisms used for in-band management are via virtual terminal access (i.e. Telnet or SSH), SNMP, or HTTP. In all large ISPs that were interviewed, HTTP management is never used and is explicitly disabled. Note that file transfer protocols (TFTP, FTP, SCP) will be covered in the 'Software Upgrades and Configuration Integrity/ Validation' section. 2.2.1. Threats / Attacks For in-band device management, passive attacks are possible if someone has the capability to intercept data between the management device and the managed device. The threat is possible if a single infrastructure device is somehow compromised and can act as a network sniffer or if it is possible to insert a new device which acts as a network sniffer. Active attacks are possible for both on-path and off-path scenarios. For on-path active attacks, the situation is the same as for a passive attack, where either a device has to already be compromised or a device can be inserted into the path. For off-path active attacks, the attack is generally limited to message insertion or modification. 2.2.1.1. Confidentiality Violations Confidentiality violations can occur when a miscreant intercepts confidential data that has been sent in cleartext. This includes interception of usernames and passwords with which an intruder can obtain unauthorized access to network devices. It can also include other information such as logging or configuration information if an administrator is remotely viewing local logfiles or configuration information. 2.2.1.2. Offline Cryptographic Attacks If username/password information was encrypted but the cryptographic mechanism used made it easy to capture data and break the encryption key, the device management traffic could be compromised. The traffic Kaeo Expires January 18, 2006 [Page 11] Internet-Draft OPSEC Practices July 2005 would need to be captured either by eavesdropping on the network or by being able to divert traffic to a malicious user. 2.2.1.3. Replay Attacks For a replay attack to be successful, in-band management traffic would need to first be captured either on-path or diverted to an attacker to later be replayed to the intended recipient. 2.2.1.4. Message Insertion/Deletion/Modification Data can be manipulated by someone in control of intermediary hosts. Forging data is also possible with IP spoofing, where a remote host sends out packets which appear to come from another, trusted host. 2.2.1.5. Man-In-The-Middle A man-in-the-middle attack attacks the identity of a communicating peer rather than the data stream itself. The attacker intercepts traffic that is sent from an in-band management system to the networking infrastructure device and traffic that is sent from the network infrastructure device to the in-band management system. 2.2.2. Security Practices All in-band management access to layer 2 and layer 3 devices is authenticated. The user authentication and authorization is typically controlled by a AAA server (i.e. RADIUS and/or TACACS+). Credentials used to determine the identity of the user vary from static username/password to one-time username/password scheme such as Secure-ID. Static username/passwords are expired after a specified period of time, usually 30 days. Every authenticated entity via AAA is an individual user for greater granularity of control. In some deployments, The AAA servers used for in-band management authentication/authorization/accounting are on separate out-of-band networks to provide a demarcation for any other authentication functions. For backup purposes, there is often a single local database entry for authentication which is known to a very limited set of key personnel. It is usually the highest privilege level username/password combination, which in most cases is the same across all devices. This local device password is routinely regenerated once every 2-3 months and is also regenerated immediately after an employee who had access to that password leaves the company or is no longer authorized to have knowledge of that password. Each individual user in the AAA database is configured with specific Kaeo Expires January 18, 2006 [Page 12] Internet-Draft OPSEC Practices July 2005 authorization capability. Specific commands are either individually denied or permitted depending on the capability of the device to be accessed. Multiple privilege levels are deployed. Most individuals are authorized with basic authorization to perform a minimal set of commands while a subset of individuals are authorized to perform more privileged commands. SSH is always used for virtual terminal access to provide for an encrypted communication channel. There are exceptions due to equipment limitations which are described in the additional considerations section. If SNMP is used for in-band management, it is for read queries only and restricted to specific hosts. The community strings are carefully chosen to be difficult to crack and there are procedures in place to change these community strings between 30-90 days. If systems support two SNMP community strings, the old string is replaced by first configuring a second newer community string and then migrating over from the currently used string to the newer one. Most large ISPs have multiple SNMP systems accessing their routers so it takes more then one maintenance period to get all the strings fixed in all the right systems. SNMP RW is not used and disabled by configuration. Access control is strictly enforced for infrastructure devices by using stringent filtering rules. A limited set of IP addresses are allowed to initiate connections to the infrastructure devices and are specific to the services which they are to limited to (i.e. SSH and SNMP). All in-band device management access is audited and any violations trigger alarms which initiate automated email, pager and/or telephone notifications. AAA servers keeps track of the authenticated entity as well as all the commands that were carried out on a specific device. Additionally, the device itself logs any access control violations (i.e. if an SSH request comes in from an IP address which is not explicitly permitted, that event is logged so that the offending IP address can be tracked down and investigations made as to why it was trying to access a particular infrastructure device) 2.2.3. Security Services The following security services are offered through the use of the practices described in the previous section: o User Authentication - All individuals are authenticated via AAA services. Kaeo Expires January 18, 2006 [Page 13] Internet-Draft OPSEC Practices July 2005 o User Authorization - All individuals are authorized via AAA services to perform specific operations once successfully authenticated. o Data Origin Authentication - Management traffic is strictly filtered to allow only specific IP addresses to have access to the infrastructure devices. This does not alleviate risk from spoofed traffic. Using SSH for device access ensures that noone can spoof the traffic during the SSH session. o Access Control - In-band management traffic is filtered to allow only specific IP addresses to have access to the infrastructure devices. o Data Integrity - Using SSH provides data integrity and ensures that noone has altered the management data in transit. o Data Confidentiality - Using SSH provides data confidentiality. o Auditing / Logging - Using AAA provides an audit trail for who accessed which device and which operations were performed. o DoS Mitigation - Using packet filters to allow only specific IP addresses to have access to the infrastructure devices. This limits but does not prevent spoofed DoS attacks directed at an infrastructure device. Often OOB management is used to lower that risk. 2.2.4. Additional Considerations Password selection for any in-band device management protocol used is critical to ensure that the passwords are hard to guess or break using a brute-force attack. IPsec is considered too difficult to deploy and the common protocol to provide for confidential in-band management access is SSH. There are exceptions for using SSH due to equipment limitations since SSH may not be supported on legacy equipment. Also, in the case where the SSH key is stored on a route processor card, a re-keying of SSH would be required whenever the route processor card needs to be swapped. Some providers feel that this operational impact exceeds the security necessary and instead use Telnet from trusted inside hosts (called 'jumphosts') to manage those devices. An individual would first SSH to the jumphost and then Telnet from the jumphost to the actual infrastructure device. All authentication and authorization is still carried out using AAA servers. In instances where Telnet access is used, the logs on the AAA servers Kaeo Expires January 18, 2006 [Page 14] Internet-Draft OPSEC Practices July 2005 are more verbose and more attention is paid to them to detect any abnormal behavior. The jumphosts themselves are carefully controlled machines and usually have limited access. Note that Telent is NEVER allowed to an infrastructure device except from specific jumphosts; i.e. packet filters are used to ensure that Telnet is only allowed from specific IP addresses. With thousands of devices to manage, some ISPs have created automated mechanisms to authenticate to devices. Kerberos is used to automate the authentication process. An individual would first log in to a Kerberized UNIX server using SSH and generate a Kerberos 'ticket'. This 'ticket' is generally set to have a lifespan of 10 hours and is used to automatically authenticate the individual to the infrastructure devices. In instances where SNMP is used, some legacy devices only support SNMPv1 which then requires the provider to mandate its use across all infrastructure devices for operational simplicity. SNMPv2 is primarily deployed since it is easier to set up than v3. 2.3. Device Out-of-Band Management Out-of-band management is generally considered to be device access where the control traffic takes a separate path as the data which traverses the network. Console access is always architected via an OOB network. SNMP management is also usually carried out via that same OOB network infrastructure. 2.3.1. Threats / Attacks For OOB device management, passive attacks are possible if someone has the capability to intercept data between the management device and the managed device. The threat is possible if a single infrastructure device is somehow compromised and can act as a network sniffer or if it is possible to insert a new device which acts as a network sniffer. Active attacks are possible for both on-path and off-path scenarios. For on-path active attacks, the situation is the same as for a passive attack, where either a device has to already be compromised or a device can be inserted into the path. For off-path active attacks, the attack is generally limited to message insertion or modification. 2.3.1.1. Confidentiality Violations Confidentiality violations can occur when a miscreant intercepts any of the OOB management data that has been sent in cleartext. This Kaeo Expires January 18, 2006 [Page 15] Internet-Draft OPSEC Practices July 2005 includes interception of usernames and passwords with which an intruder can obtain unauthorized access to network devices. It can also include other information such as logging or configuration information if an administrator is remotely viewing local logfiles or configuration information. 2.3.1.2. Offline Cryptographic Attacks If username/password information was encrypted but the cryptographic mechanism used made it easy to capture data and break the encryption key, the OOB management traffic could be compromised. The traffic would need to be captured either by eavesdropping on the network or by being able to divert traffic to a malicious user. 2.3.1.3. Replay Attacks For a replay attack to be successful, the OOB management traffic would need to first be captured either on-path or diverted to an attacker to later be replayed to the intended recipient. 2.3.1.4. Message Insertion/Deletion/Modification Data can be manipulated by someone in control of intermediary hosts. Forging data is also possible with IP spoofing, where a remote host sends out packets which appear to come from another, trusted host. 2.3.1.5. Man-In-The-Middle A man-in-the-middle attack attacks the identity of a communicating peer rather than the data stream itself. The attacker intercepts traffic that is sent from an OOB management system to the networking infrastructure device and traffic that is sent from the network infrastructure device to the OOB management system. 2.3.2. Security Practices OOB is done via a terminal server at each location. SSH access is used to get to the terminal server from where sessions to the devices are initiated. Dial-in access is deployed as a backup if the network is not available. All OOB management access to layer 2 and layer 3 devices is authenticated. The user authentication and authorization is typically controlled by a AAA server (i.e. RADIUS and/or TACACS+). Credentials used to determine the identity of the user vary from static username/password to one-time username/password scheme such as Secure-ID. Static username/passwords are expired after a specified period of time, usually 30 days. Every authenticated entity via AAA Kaeo Expires January 18, 2006 [Page 16] Internet-Draft OPSEC Practices July 2005 is an individual user for greater granularity of control. Note that often the AAA server used for OOB management authentication is a separate physical device from the AAA server used for in-band management user authentication. For backup purposes, there is often a single local database entry for authentication which is known to a very limited set of key personnel. It is usually the highest privilege level username/password combination, which in most cases is the same across all devices. This local device password is routinely regenerated once every 2-3 months and is also regenerated immediately after an employee who had access to that password leaves the company or is no longer authorized to have knowledge of that password. Each individual user in the AAA database is configured with specific authorization capability. Specific commands are either individually denied or permitted depending on the capability of the device to be accessed. Multiple privilege levels are deployed. Most individuals are authorized with basic authorization to perform a minimal set of commands while a subset of individuals are authorized to perform more privileged commands. Some OOB management functions are performed using command line interface (CLI) scripting. In these scenarios, a dedicated user is used for the identity in scripts that perform CLI scripting. Once authenticated, these scripts control which commands are legitimate depending on authorization rights of the authenticated individual. SSH is always used for virtual terminal access to provide for an encrypted communication channel. There are exceptions due to equipment limitations which are described in the additional considerations section. If SNMP is used for OOB management, it is for read queries only and restricted to specific hosts. The community strings are carefully chosen to be difficult to crack and there are procedures in place to change these community strings between 30-90 days. If systems support two SNMP strings, a second new string is set and then migrate over from the 1st to the 2nd. Most large ISPs have multiple SNMP systems accessing their routers so it takes more then one maintenance period to get all the strings fixed in all the right systems. SNMP RW is not used and disabled by configuration. Access control is strictly enforced for infrastructure devices by using stringent filtering rules. A limited set of IP addresses are allowed to initiate connections to the infrastructure devices and are specific to the services which they are to limited to (i.e. SSH and SNMP). Kaeo Expires January 18, 2006 [Page 17] Internet-Draft OPSEC Practices July 2005 All OOB device management access is audited. The AAA server keeps track of the authenticated entity as well as all the commands that were carried out on a specific device. Additionally, the device itself logs any access control violations (i.e. if an SSH request comes in from an IP address which is not explicitly permitted, that event is logged so that the offending IP address can be tracked down and investigations made as to why it was trying to access a particular infrastructure device) 2.3.3. Security Services The security services offered for device OOB management are nearly identical to those of device in-band management. Due to the critical nature of controlling and limiting device access, many ISPs feel that physically separating the management traffic from the normal customer data traffic will provide an added level of risk mitigation and limit the potential attack vectors. For OOB management, the security services offered through the use of the practices described in the previous section are: o User Authentication - All individuals are authenticated via AAA services. o User Authorization - All individuals are authorized via AAA services to perform specific operations once successfully authenticated. o Data Origin Authentication - Management traffic is strictly filtered to allow only specific IP addresses to have access to the infrastructure devices. This does not alleviate risk from spoofed traffic. Using SSH for device access ensures that noone can spoof the traffic during the SSH session. o Access Control - In-band management traffic is filtered to allow only specific IP addresses to have access to the infrastructure devices. o Data Integrity - Using SSH provides data integrity and ensures that noone has altered the management data in transit. o Data Confidentiality - Using SSH provides data confidentiality. o Auditing / Logging - Using AAA provides an audit trail for who accessed which device and which operations were performed. o DoS Mitigation - Using packet filters to allow only specific IP addresses to have access to the infrastructure devices. This Kaeo Expires January 18, 2006 [Page 18] Internet-Draft OPSEC Practices July 2005 limits but does not prevent spoofed DoS attacks directed at an infrastructure device. However, the risk is lowered by using a separate physical network for management purposes. 2.3.4. Additional Considerations Password selection for any OOB device management protocol used is critical to ensure that the passwords are hard to guess or break using a brute-force attack. IPsec is considered too difficult to deploy and the common protocol to provide for confidential OOB management access is SSH. There are exceptions for using SSH due to equipment limitations since SSH may not be supported on legacy equipment. Also, in the case where the SSH key is stored on a route processor card, a re-keying of SSH would be required whenever the route processor card needs to be swapped. Some providers feel that this operational impact exceeds the security necessary and instead use Telnet from trusted inside hosts (called 'jumphosts') to manage those device. An individual would first SSH to the jumphost and then Telnet from the jumphost to the terminal server before logging in to the device console. All authentication and authorization is still carried out using AAA servers. In instances where Telnet access is used, the logs on the AAA servers are more verbose and more attention is paid to them to detect any abnormal behavior. The jumphosts themselves are carefully controlled machines and usually have limited access. Note that Telent is NEVER allowed to an infrastructure device except from specific jumphosts; i.e. packet filters are used at the console server and/or infrastructure device to ensure that Telnet is only allowed from specific IP addresses. In instances where SNMP is used, some legacy devices only support SNMPv1 which then requires the provider to mandate its use across all infrastructure devices for operational simplicity. SNMPv2 is primarily deployed since it is easier to set up than v3. 2.4. Data Path This section refers to how traffic is handled which traverses the network infrastructure device. The primary goal of ISPs is to forward customer traffic. However, due to the large amount of malicious traffic that can cause DoS attacks and render the network unavailable, specific measures are sometimes deployed to ensure the availability to forward legitimate customer traffic. Kaeo Expires January 18, 2006 [Page 19] Internet-Draft OPSEC Practices July 2005 2.4.1. Threats / Attacks Any data traffic can potentially be attack traffic and the challenge is to detect and potentially stop forwarding any of the malicious traffic. The deliberately sourced attack traffic can consist of packets with spoofed source and/or destination addresses or any other malformed packet which mangle any portion of a header field to cause protocol-related security issues (such as resetting connections, causing unwelcome ICPM redirects, creating unwelcome IP options or packet fragmentations). 2.4.2. Security Practices Filtering and rate limiting are the primary mechanism to provide risk mitigation of malicious traffic rendering the ISP services unavailable. However, filtering and rate limiting of data path traffic is deployed in a variety of ways depending on how automated the process is and what the capabilities and performance limitations of existing deployed hardware are. The ISPs which do not have performance issues with their equipment follow BCP38 [BCP38] guidelines. Null routes and black-hole filtering are used to deter any detected malicious traffic streams. Most ISPs consider layer 4 filtering useful but it is only implemented if there is no performance limitations on the devices. Netflow is used for tracking traffic flows but there is some concern whether sampling is good enough to detect malicious behavior. Unicast RPF is not consistently implemented. Some ISPs are in process of doing so while other ISPs think that the perceived benefit of knowing that spoofed traffic comes from legitimate addresses are not worth the operational complexity. Some providers have a policy of implementing uRPF at link speeds of DS3 and below. 2.4.3. Security Services o User Authentication - Not applicable o User Authorization - Not applicable o Data Origin Authentication - When IP address filtering per BCP38 and uRPF are deployed at network edges it can ensure that any spoofed traffic comes from at least a legitimate IP address and can be tracked. o Access Control - IP address filtering and layer 4 filtering is used to deny forbidden protocols and limit traffic destined for Kaeo Expires January 18, 2006 [Page 20] Internet-Draft OPSEC Practices July 2005 infrastructure device itself. o Data Integrity - Not applicable o Data Confidentiality - Not applicable o Auditing / Logging - Filtering exceptions are logged for potential attack traffic. o DoS Mitigation - Black-hole triggered filtering and rate-limiting are used to limit the risk of DoS attacks. 2.4.4. Additional Considerations For layer 2 devices, MAC address filtering and authentication is not used. This is due to the problems it can cause when troubleshooting networking issues. Port security becomes unmanageable at a large scale where 1000s of switches are deployed. Rate limiting is used by some ISPs although other ISPs believe it is not really useful since attackers are not well behaved and it doesn't provide any operational benefit over the complexity. Rate limiting may be improved by developing flow-based rate-limiting capabilities with filtering hooks. This would improve the performance as well as the granularity over current capabilities. Lack of consistency regarding the ability to filter, especially with respect to performance issues cause some ISPs to not implement BCP38 guidelines for ingress filtering. One such example is at edge boxes where you have up to 1000 T1's connecting into a router with an OC-12 uplink. Some deployed devices experience a large performance impact with filtering which is unacceptable for passing customer traffic through. Where performance is not an issue, the ISPs make a tradeoff between management versus risk. 2.5. Routing Control Plane The routing control plane deals with all the traffic which is part of establishing and maintaining routing protocol information. 2.5.1. Threats / Attacks Attacks on the routing control plane can be both from passive or active sources. Passive attacks are possible if someone has the capability to intercept data between the communicating routing peers. This can be accomplished if a single routing peer is somehow compromised and can act as a network sniffer or if it is possible to insert a new device which acts as a network sniffer. Kaeo Expires January 18, 2006 [Page 21] Internet-Draft OPSEC Practices July 2005 Active attacks are possible for both on-path and off-path scenarios. For on-path active attacks, the situation is the same as for a passive attack, where either a device has to already be compromised or a device can be inserted into the path. This may lead to an attacker impersonating a legitimate routing peer and exchanging routing information. Unintentional active attacks are more common due to configuration errors, which cause legitimate routing peers to feed invalid routing information to other neighboring peers. For off-path active attacks, the attacks are generally limited to message insertion or modification which can divert traffic to illegitimate destinations and cause traffic to never reach its intended destination. 2.5.2. Confidentiality Violations Confidentiality violations can occur when a miscreant intercepts any of the routing update traffic. This is becoming more of a concern because many ISPs are classifying addressing schemes and network topologies as private and proprietary information. It is also a concern because the routing protocol packets contain information that may show ways in which routing sessions could be spoofed or hijacked. This in turn could lead into a man-in-the-middle attack where the miscreants can insert themselves into the traffic path or divert the traffic path and violate the confidentiality of user data. 2.5.3. Offline Cryptographic Attacks If any cryptographic mechanism was used to provide for data integrity and confidentiality, an offline cryptographic attack could potentially compromise the data. The traffic would need to be captured either by eavesdropping on the network or by being able to divert traffic to a malicious user. Note that by using cryptographically protected routing information, the latter would require the cryptographic key to already be compromised anyway so this attack is only feasible if a device was able eavesdrop and capture the cryptographically protected routing information. 2.5.4. Replay Attacks For a replay attack to be successful, the routing control plane traffic would need to first be captured either on-path or diverted to an attacker to later be replayed to the intended recipient. 2.5.5. Message Insertion/Deletion/Modification Routing control plane traffic can be manipulated by someone in control of intermediate hosts. In addition, traffic can be injected Kaeo Expires January 18, 2006 [Page 22] Internet-Draft OPSEC Practices July 2005 by forging IP addresses, where a remote router sends out packets which appear to come from another, trusted router. If enough traffic is injected to be processed by limited memory routers it can cause a DoS attack. 2.5.6. Man-In-The-Middle A man-in-the-middle attack attacks the identity of a communicating peer rather than the data stream itself. The attacker intercepts traffic that is sent from one routing peer to the other and communicates on behalf of one of the peers. This can lead to diversion of the user traffic to either an unauthorized receiving party or cause legitimate traffic to never reach its intended destination. 2.5.7. Security Practices Securing the routing control plane takes many features which are generally deployed as a system. MD5 authentication is used by some ISPs to validate the sending peer and to ensure that the data in transit has not been altered. Some ISPs only deploy MD-5 authentication at customer's request. Additional sanity checks to ensure with reasonable certainty that the received routing update was originated by a valid routing peer include route filters and the BTSH feature [BTSH]. Note that validating whether a legitimate peer has the authority to send the contents of the routing update is a difficult problem that needs yet to be resolved. In the case of BGP routing, a variety of policies are deployed to limit the propagation of invalid routing information. These include: incoming and outgoing prefix filters for BGP customers, incoming and outgoing prefix filters for peers and upstream neighbors, incoming AS-PATH filter for BGP customers, outgoing AS-PATH filter towards peers and upstream neighbors, route dampening and rejecting selected attributes and communities. Consistency between these policies varies greatly although there is a trend to start depending on AS- PATH filters because they are much more manageable than the large numbers of prefix filters that would need to be maintained. Many ISPs also do not propagate interface IP addresses to further reduce attack vectors on routers and connected customers. 2.5.8. Security Services o User Authentication - Not applicable o User Authorization - Not applicable Kaeo Expires January 18, 2006 [Page 23] Internet-Draft OPSEC Practices July 2005 o Data Origin Authentication - By using MD5 authentication and/or the TTL-hack a routing peer can be reasonably certain that traffic originated from a valid peer. o Access Control - Route filters, AS-PATH filters and prefix limits are used to control access to specific parts of the network. o Data Integrity - By using MD5 authentication a peer can be reasonably certain that the data has not been modified in transit but there is no mechanism to prove the validity of the routing information itself. o Data Confidentiality - Not implemented o Auditing / Logging - Filter exceptions are logged. o DoS Mitigation - Many DoS attacks are mitigated using a combination of techniques including: MD5 authentication, the BTSH feature, filtering routing advertisements to bogons and filtering routing advertisements to one's own network. 2.5.9. Additional Considerations So far the primary concern to secure the routing control plane has been to validate the sending peer and to ensure that the data in transit has not been altered. Although MD-5 routing protocol extensions have been implemented which can provide both services, they are not consistently deployed amongst ISPs. Two major deployment concerns have been implementation issues where both software bugs and the lack of graceful re-keying options have caused significant network down times. Also, some ISPs express concern that deploying MD5 authentication will itself be a worse DoS attack victim and prefer to use a combination of other risk mitigation mechanisms such as BTSH and route filters. Route filters are used to limit what routes are believed from a valid peer. Packet filters are used to limit which systems can appear as a valid peer. Due to the operational constraints of maintaining large prefix filter lists, many ISPs are starting to depend on BGP AS-PATh filters to/from their peers and upstream neighbors. IPsec is not deployed since the operational management aspects of ensuring interoperability and reliable configurations is too complex and time consuming to be operationally viable. There is also limited concern to the confidentiality of the routing information. The integrity and validity of the updates are of much greater concern. There is concern for manual or automated actions which introduce new Kaeo Expires January 18, 2006 [Page 24] Internet-Draft OPSEC Practices July 2005 routes and can affect the entire routing domain. 2.6. Software Upgrades and Configuration Integrity / Validation Software upgrades and configuration changes are usually performed as part of either in-band or OOB management functions. However, there are additional considerations to be taken into account which are enumerated in this section. 2.6.1. Threats / Attacks Attacks performed on system software and configurations can be both from passive or active sources. Passive attacks are possible if someone has the capability to intercept data between the network infrastructure device and the system which is downloading or uploading the software or configuration information. This can be accomplished if a single infrastructure device is somehow compromised and can act as a network sniffer or if it is possible to insert a new device which acts as a network sniffer. Active attacks are possible for both on-path and off-path scenarios. For on-path active attacks, the situation is the same as for a passive attack, where either a device has to already be compromised or a device can be inserted into the path. For off-path active attacks, the attacks are generally limited to message insertion or modification where the attacker may wish to load illegal software or configuration files to an infrastructure device. 2.6.2. Confidentiality Violations Confidentiality violations can occur when a miscreant intercepts any of the software image or configuration information. The software image may give an indication of exploits which the device is vulnerable to while the configuration information can inadvertently lead attackers to identify critical infrastructure IP addresses and passwords. 2.6.3. Offline Cryptographic Attacks If any cryptographic mechanism was used to provide for data integrity and confidentiality, an offline cryptographic attack could potentially compromise the data. The traffic would need to be captured either by eavesdropping on the network or by being able to divert traffic to a malicious user. 2.6.4. Replay Attacks For a replay attack to be successful, the software image or Kaeo Expires January 18, 2006 [Page 25] Internet-Draft OPSEC Practices July 2005 configuration file would need to first be captured either on-path or diverted to an attacker to later be replayed to the intended recipient. 2.6.5. Message Insertion/Deletion/Modification Software images and configuration files can be manipulated by someone in control of intermediate hosts. By forging an IP address and impersonating a valid host which can download software images or configuration files, invalid files can be downloaded to an infrastructure device. An invalid software image or configuration file can cause a device to hang and become inoperable. Spoofed configuration files can be hard to detect, especially when the only added command is to allow a miscreant access to that device by entering a filter allowing a specific host access and configuring a local username/password database entry for authentication to that device. 2.6.6. Man-In-The-Middle A man-in-the-middle attack attacks the identity of a communicating peer rather than the data stream itself. The attacker intercepts traffic that is sent between the infrastructure device and the host used to upload/download the system image or configuration file. He/ she can then act on behalf of one or both of these systems. If an attacker obtained a copy of the software image being deployed, he could potentially exploit a known vulnerability and gain access to the system. From a captured configuration file, he could obtain confidential network topology information or even more damaging information if any of the passwords in the configuration file were not encrypted. 2.6.7. Security Practices Images and configurations are stored on specific hosts which have limited access. All access and activity relating to these hosts are authenticated and logged via AAA services. When uploaded/downloading any system software or configuration files, either TFTP, FTP or SCP can be used. Where possible, SCP is used to secure the data transfer and FTP is generally never used. All TFTP and SCP access is username/password authenticated and in most environments scripts are used for maintaining a large number of routers. To ensure the integrity of the configurations, every hour the configuration files are polled and compared to the previously polled version to find discrepancies. In at least one environment these tools are Kerberized to take advantage of automated authentication (not confidentiality). Kaeo Expires January 18, 2006 [Page 26] Internet-Draft OPSEC Practices July 2005 Filters are used to limit access to uploading/downloading configuration files and system images to specific IP addresses and protocols. The software images perform CRC-checks but many ISPs expressed interest in having software image integrity validation based on the MD5 algorithm for enhanced security. The system binaries use the MD5 algorithm to validate integrity. In all configuration files, the passwords are stored in an obfuscated format. This includes passwords for user authentication, MD5 shared secrets, AAA server shared secrets, NTP shared secrets, etc. For older software which may not support this functionality, configuration files are stored with passwords in readable format. [is this true? are configuration files then protected? if passwords in readable format, is the thought that an OOB management network with SCP will be enough protection? ] Automated security validation is performed on infrastructure devices using nmap and nessus to ensure valid configuration against many of the well-known attacks. 2.6.8. Security Services o User Authentication - All users are authenticated before being able to download/upload any system images or configuration files. o User Authorization - All authenticated users are granted specific privileges to download or upload system images and/or configuration files. o Data Origin Authentication - Filters are used to limit access to uploading/downloading configuration files and system images to specific IP addresses. o Access Control - Filters are used to limit access to uploading/ downloading configuration files and system images to specific IP addresses and protocols. o Data Integrity - All systems use either a CRC-check or MD5 authentication to ensure data integrity. o Data Confidentiality - If the SCP protocol is used then there is confidentiality of the downloaded/uploaded configuration files and system images. Kaeo Expires January 18, 2006 [Page 27] Internet-Draft OPSEC Practices July 2005 o Auditing / Logging - All access and activity relating to downloading/uploading system images and configuration files are logged via AAA services and filter exception rules. o DoS Mitigation - TBD 2.6.9. Additional Considerations Where the MD5 algorithm is not used to perform data integrity checking of software images and configuration files, ISPs have expressed an interest in having this functionality. IPsec is considered too cumbersome and operationally difficult to use for data integrity and confidentiality. 2.7. Logging Considerations Although logging is part of all the previous sections, it is important enough to be covered as a separate item. The main issues revolve around what gets logged, how long are logs kept and what mechanisms are used to secure the logged information while it is in transit and while it is stored. 2.7.1. Threats / Attacks Attacks on the logged data can be both from passive or active sources. Passive attacks are possible if someone has the capability to intercept data between the recipient logging server and the device the logged data originated from. This can be accomplished if a single infrastructure device is somehow compromised and can act as a network sniffer or if it is possible to insert a new device which acts as a network sniffer. Active attacks are possible for both on-path and off-path scenarios. For on-path active attacks, the situation is the same as for a passive attack, where either a device has to already be compromised or a device can be inserted into the path. For off-path active attacks, the attacks are generally limited to message insertion or modification which can alter the logged data to keep any compromise from being detected or to destroy any evidence which could be used for criminal prosecution. 2.7.1.1. Confidentiality Violations Confidentiality violations can occur when a miscreant intercepts any of the logging data which is in transit on the network. This could lead to privacy violations if some of the logged data has not been sanitized to disallow any data that could be a violation of privacy to be included in the logged data. Kaeo Expires January 18, 2006 [Page 28] Internet-Draft OPSEC Practices July 2005 2.7.1.2. Offline Cryptographic Attacks If any cryptographic mechanism was used to provide for data integrity and confidentiality, an offline cryptographic attack could potentially compromise the data. The traffic would need to be captured either by eavesdropping on the network or by being able to divert traffic to a malicious user. 2.7.1.3. Replay Attacks For a replay attack to be successful, the logging data would need to first be captured either on-path or diverted to an attacker and later replayed to the recipient. [is reply handled by syslog protocol?] 2.7.1.4. Message Insertion/Deletion/Modification Logging data could be injected, deleted or modified by someone in control of intermediate hosts. Logging data can also be injected by forging packets from either legitimate or illegitimate IP addresses. 2.7.1.5. Man-In-The-Middle A man-in-the-middle attack attacks the identity of a communicating peer rather than the data stream itself. The attacker intercepts traffic that is sent between the infrastructure device and the logging server or traffic sent between the logging server and the database which is used to archive the logged data. Any unauthorized access to logging information could lead to knowledge of private and proprietary network topology information which could be used to compromise portions of the network. An additional concern is having access to logging information which could be deleted or modified so as to cover any traces of a security breach. 2.7.2. Security Practices Logging is mostly performed on an exception auditing basis when it comes to filtering (i.e. traffic which is NOT allowed is logged). Typically the data logged will contain the source and destination IP addresses and layer 4 port numbers as well as a timestamp. The syslog protocol is used to transfer the logged data between the infrastructure device to the syslog server. Many ISPs use the OOB management network to transfer syslog data since there is virtually no security performed between the syslog server and the device. All ISPs have multiple syslog servers - some ISPs choose to use separate syslog servers for varying infrastructure devices (i.e. one syslog server for backbone routers, one syslog server for customer edge routers, etc.) Kaeo Expires January 18, 2006 [Page 29] Internet-Draft OPSEC Practices July 2005 The timestamp is derived from NTP which is generally configured as a flat hierarchy at stratum1 and stratum2 to have less configuration and less maintenance. Each router is configured with one stratum1 peer both locally and remotely. In addition to logging filtering exceptions, the following is typically logged: Routing protocol state changes, all device access (regardless of authentication success or failure), all commands issued to a device, all configuration changes and all router events (boot-up/flaps). The main function of any of these log messages is to see what the device is doing as well as to try and ascertain what certain malicious attackers are trying to do. Some ISPs put in passive devices to see routing updates and withdrawals and not rely solely on the device for log files. This provides a backup mechanism to see what is going on in the network in the event that a device may 'forget' to do syslog if the CPU is busy. The logs from the various syslog server devices are generally transferred into databases at a set interval which can be anywhere from every 10 minutes to every hour. One ISP uses Rsync to push the data into a database and then the information is sorted manually by someone SSH'ing to that database. 2.7.3. Security Services o User Authentication - Not applicable o User Authorization - Not applicable o Data Origin Authentication - Not implemented o Access Control - Filtering on logging host and server IP address to ensure that syslog information only goes to specific syslog hosts. o Data Integrity - Not implemented o Data Confidentiality - Not implemented o Auditing / Logging - This entire section deals with logging. o DoS Mitigation - TBD Kaeo Expires January 18, 2006 [Page 30] Internet-Draft OPSEC Practices July 2005 2.7.4. Additional Considerations There is no security with syslog and ISPs are fully cognizant of this. IPsec is considered too operationally expensive and cumbersome to deploy. Syslog-ng and stunnel are being looked at for providing better authenticated and integrity protected solutions. Mechanisms to prevent unauthorized personnel from tampering with logs is constrained to auditing who has access to the logging servers and files. ISPs expressed requirements for more than just UDP syslog. They would also like more granular and flexible facilities and priorities, i.e. specific logs to specific servers. 2.8. Filtering Considerations Although filtering has been covered under many of the previous sections, this section will provide some more insights to the filtering considerations that are currently being taken into account. Filtering is now being categorized into three specific areas: data plane, management plane and routing control plane. 2.8.1. Data Plane Filtering Data plane filters control the traffic that traverses through a device and affect transit traffic. Most ISPs deploy these kinds of filters at the customer facing edge devices to mitigate spoofing attacks. 2.8.2. Management Plane Filtering Management filters control the traffic to and from a device. All of the protocols which are used for device management fall under this category and includes SSH, Telnet, SNMP, NTP, http, DNS, TFTP, FTP, SCP and Syslog. This type of traffic is currently filtered per interface and is based on any combination of protocol, source and destination IP address and source and destination port number. Note that logging the filtering rules can today place a burden on many systems and more granularity is often required to more specifically log the required exceptions. IPv6 networks require the use of specific ICMP messages for proper protocol operation. Therefore, ICMP cannot be completely filtered to and from a device. Instead, granular ICMPv6 filtering is always deployed to allow for specific ICMPv6 types to be sourced or destined to a network device. Kaeo Expires January 18, 2006 [Page 31] Internet-Draft OPSEC Practices July 2005 2.8.3. Routing Control Plane Filtering Routing filters are used to control the flow of routing information. In IPv6 networks, some providers are liberal in accepting /48Os due to the still unresolved multihoming issues. Anything longer than a /48 is discarded on EBGP. 2.9. Denial of Service Tracking / Tracing Denial of Service attacks are an ever increasing problem and require vast amounts of resources to combat effectively. Some large ISPs do not concern themselves with attack streams that are less than 1G in bandwidth - this is on the larger pipes where 1G is essentially less than 5% of offered load. This is largely due to the large amounts of DDoS traffic which continually requires investigation and mitigation. At last count the number of hosts making up large distributed DoS BOTnets exceeded 1 million hosts. New techniques are continually evolving to automate the process of detecting DoS sources and mitigating any adverse effects as quickly as possible. At this time, ISPs are using a variety of mitigation techniques including: sink hole routing, black-hole triggered routing, uRPF and rate limiting. Each of these techniques will be detailed below. 2.9.1. Sink Hole Routing Sink hole routing refers to injecting a more specific route for any known attack traffic which will ensure that the malicious traffic is redirected to a valid subnet or specific IP address where it can be analyzed. 2.9.2. Black-Hole Triggered Routing Black-hole triggered routing is a technique where the BGP routing protocol is used to propagate static routes which in turn redirects attack traffic to the null interface where it is effectively dropped. This technique is often used in large routing infrastructures since BGP can propagate the information in a fast effective manner as opposed to using any packet-based filtering techniques on hundreds or thousands of routers. 2.9.3. Unicast Reverse Path Forwarding Unicast Reverse Path Forwarding (uRPF) is a mechanism for validating whether an incoming packet has a legitimate source address or not. It has two modes: strict mode and loose mode. In strict mode, uRPF checks whether the incoming packet has a source address that matches Kaeo Expires January 18, 2006 [Page 32] Internet-Draft OPSEC Practices July 2005 a prefix in the routing table, and whether the interface expects to receive a packet with this source address prefix. If the incoming packet fails the unicast RPF check, the packet is not accepted on the incoming interface. Loose mode uRPF is not as specific and the incoming packet is accepted if there is any route in the routing table for the source address. uRPF is not used on interfaces that are likely to have routing asymmetry, meaning multiple routes to the source of a packet. Usually for ISPs, uRPF is placed at the customer edge of a network. 2.9.4. Rate Limiting Rate limiting refers to allocating a specific amount of bandwidth or packets per second to specific traffic types. This technique is widely used to mitigate well-known protocol attacks such as the TCP- SYN attack where a large number of resources get allocated for spoofed TCP traffic. Although this technique does not stop an attack, it can lessen the damage and impact on a specific service. Kaeo Expires January 18, 2006 [Page 33] Internet-Draft OPSEC Practices July 2005 3. Security Considerations This entire document deals with current security practices in large ISP environments. As a synopsis, a table is shown below which summarizes the operational functions which are to be protected and the security services which currently deployed security practices offer: [ Table to be added ] 4. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2828] Shirey, R., "Internet Security Glossary", RFC 2828, May 2000. [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, July 2003. Kaeo Expires January 18, 2006 [Page 34] Internet-Draft OPSEC Practices July 2005 Appendix A. Acknowledgments The editor gratefully acknowledges the contributions of: George Jones, who has been instrumental in providing guidance and direction for this document and the insighful comments from Ross Callon and the numerous ISP operators who supplied the information which is depicted in this document. Kaeo Expires January 18, 2006 [Page 35] Internet-Draft OPSEC Practices July 2005 Appendix B. Protocol Specific Attacks This section will enumerate many of the traditional protocol based attacks which have been observed over the years to cause malformed packets and/or exploit protocol deficiencies. B.1. Layer 2 Attacks o ARP Flooding B.2. IPv4 Attacks o IP Stream Option o IP Address Spoofing o IP Source Route Option o IP Short header o IP Malformed Packet o Ip Bad Option o Ip Address Session Limit o Fragmenmts - too many o Fragments - large offset o Fragments - same offset o Fragments - reassembly with different offsets (TearDrop Attac) o Fragments - reassembly off by one IP header (Nestea Attack) o Fragment - flooding only initial fragment (Rose Attack) o IGMP oversized packet o ICMP Source Quench o ICMP Mask Request o ICMP Large Packet (> 1472) Kaeo Expires January 18, 2006 [Page 36] Internet-Draft OPSEC Practices July 2005 o ICMP Oversized packet (>65536) o ICMP Flood o ICMP Broadcast w/ Spoofed Source (Smurf Attack) o ICMP Error Packet Flood o ICMP Spoofed Unreachable o TCP Packet without Flag o TCP Oversized Packet o TCP FIN bit with no ACK bit o TCP Packet with URG/OOB flag (Nuke Attack) o SYN Fragments o SYN Flood o SYN with IP Spoofing (Land Attack) o SYN and FIN bits set o TCP port scan attack o UDP spoofed broadcast echo (Fraggle Attack) o UDP attack on diag ports (Pepsi Attack) B.3. IPv6 Attacks Any of the above-mentioned IPv4 attacks could be used in IPv6 networks with the exception of any fragmentation and broadcast traffic, which operate differently in IPv6. Today, IPv6 enabled hosts are starting to be used to create IPv6 tunnels which can effectively hide botnet and other malicious traffic if firewalls and network flow collection tools are not capable of detecting this traffic. Kaeo Expires January 18, 2006 [Page 37] Internet-Draft OPSEC Practices July 2005 Author's Address Merike Kaeo Double Shot Security, Inc. 520 Washington Blvd. #363 Marina Del Rey, CA 90292 U.S.A. Phone: +1 310 866 0165 Email: merike@doubleshotsecurity.com Kaeo Expires January 18, 2006 [Page 38] Internet-Draft OPSEC Practices July 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Kaeo Expires January 18, 2006 [Page 39]