IPv6 Operational Guidelines for Datacenters

The need for considering the aspects related to IPv4-to-IPv6 transition for all devices and services connected to the Internet has been widely mentioned elsewhere, and it is not our intention to make an additional call on it. Just let us note that many of those services are already or will soon be located in Data Centers (DC), what makes considering the issues associated to DC infrastructure transition a key aspect both for these infrastructures themselves, and for providing a simpler and clear path to service transition. All issues discussed here are related to DC infrastructure transition, and are intended to be orthogonal to whatever particular mechanisms for making the services hosted in the DC available through IPv6 beyond the specific aspects related to their deployment on the infrastructure. General mechanisms related to service transition have been discussed in depth elsewhere (see, for example and ) and are considered to be independent to the goal of this discussion. The applicability of these general mechanisms for service transition will, in many cases, depend on the supporting DC's infrastructure characteristics. However, this document intends to keep both problems (service vs. infrastructure transition) as different issues. Furthermore, the combination of the regularity and controlled management in a DC interconnection fabric with IPv6 universal end-to-end addressing should translate in simpler and faster VM migrations, either intra- or inter-DC, and even inter-provider.

This document presents a transition framework structured along transition stages and operational guidance associated with the degree of penetration of IPv6 into the DC communication fabric. It is worth noting we are using these stages as a classification mechanism, and they have not to be associated with any a succession of steps from a v4-only infrastructure to full-fledged v6, but to provide a framework that operators, users, and even manufacturers could use to assess their plans and products. There is no (explicit or implicit) requirement on starting at the stage describe in first place, nor to follow them in successive order. According to their needs and the available solutions, DC operators can choose to start or remain at a certain stage, and freely move from one to another as they see fit, without contravening this document. In this respect, the classification intends to support the planning in aspects such as the adaptation of the different transition stages to the evolution of traffic patterns, or risk assessment in what relates to deploying new components and incorporating change control, integration and testing in highly-complex multi-vendor infrastructures. Three main transition stages can be considered when analyzing IPv6 deployment in the DC infrastructure, all compatible with the availability of services running in the DC through IPv6: Experimental. The DC keeps a native IPv4 infrastructure, with gateway routers (or even application gateways when services require so) performing the adaptation to requests arriving from the IPv6 Internet. Dual stack. Native IPv6 and IPv4 are present in the infrastructure, up to whatever the layer in the interconnection scheme where L3 is applied to packet forwarding. IPv6-Only. The DC has a fully pervasive IPv6 infrastructure, including full IPv6 hypervisors, which perform the appropriate tunneling or NAT if required by internal applications running IPv4.

The diagram in Figure 1 depicts a generalized interconnection schema in a DC.

Hypervisors provide connection services (among others) to virtual machines running on physical servers. Access elements provide connectivity directly to/from physical servers. The access elements are typically placed either top-of-rack (ToR) or end-of-row(EoR). Aggregation elements group several (many) physical racks to achieve local integration and provide as much structure as possible to data paths. Core elements connect all aggregation elements acting as the DC backbone. One or several gateways connecting the DC to the Internet, Branch Offices, Partners, Third-Parties, and/or other DCs. The interconnectivity to other DC may be in the form of VPNs, WAN links, metro links or any other form of interconnection. In many actual deployments, depending on DC size and design decisions, some of these elements may be combined (core and gateways are provider by the same routers, or hypervisors act as access elements) or virtualized to some extent, but this layered schema is the one that best accommodates the different options to use L2 or L3 at any of the different DC interconnection layers, and will help us in the discussion along the document.

This transition stage corresponds to the first step that many datacenters may take (or have taken) in order to make their external services initially accessible from the IPv6 Internet and/or to evaluate the possibilities around it, and corresponds to IPv6 traffic patterns totally originated out of the DC or their tenants, being a small percentage of the total external requests. At this stage, DC network scheme and addressing do not require any important change, if any. It is important to remark that in no case this can be considered a permanent stage in the transition, or even a long-term solution for incorporating IPv6 into the DC infrastructure. This stage is only recommended for experimentation or early evaluation purposes. The translation of IPv6 requests into the internal infrastructure addressing format occurs at the outmost level of the DC Internet connection. This can be typically achieved at the DC gateway routers, that support the appropriate address translation mechanisms for those services required to be accessed through native IPv6 requests. The policies for applying adaptation can range from performing it only to a limited set of specified services to providing a general translation service for all public services. More granular mechanisms, based on address ranges or more sophisticated dynamic policies are also possible, as they are applied by a limited set of control elements. These provide an additional level of control to the usage of IPv6 routable addresses in the DC environment, which can be especially significant in the experimentation or early deployment phases this stage is applicable to. Even at this stage, some implicit advantages of IPv6 application come into play, even if they can only be applied at the ingress elements: Flow labels can be applied to enhance load-balancing, as described in . If the incoming IPv6 requests are adequately labeled the gateway systems can use the flow labels as a hint for applying load-balancing mechanisms when translating the requests towards the IPv4 internal network. During VM migration (intra- or even inter-DC), Mobile IP mechanisms can be applied to keep service availability during the transient state.

This model is also suitable to be applied in an "off-shore" mode by the service provider connecting the DC infrastructure to the Internet, as described in . When this off-shore mode is applied, the original source address will be hidden to the DC infrastructure, and therefore identification techniques based on it, such as geolocation or reputation evaluation, will be hampered. Unless there is a specific trust link between the DC operator and the ISP, and the DC operator is able to access equivalent identification interfaces provided by the ISP as an additional service, the off-shore experimental stage cannot be considered applicable when source address identification is required.

This stage requires dual-stack elements in some internal parts of the DC infrastructure. This brings some degree of partition in the infrastructure, either in a horizontal (when data paths or management interfaces are migrated or left in IPv4 while the rest migrate) or a vertical (per tenant or service group), or even both. Although it may seem an artificial case, situations requiring this stage can arise from different requirements from the user base, or the need for technology changes at different points of the infrastructure, or even the goal of having the possibility of experimenting new solutions in a controlled real-operations environment, at the price of the additional complexity of dealing with a double protocol stack, as noted in and elsewhere. This transition stage can accommodate different traffic patterns, both internal and external, though it better fits to scenarios of a clear differentiation of different types of traffic (external vs. internal, data vs management...), and/or a more or less even distribution of external requests. A common scenario would include native dual stack servers for certain services combined with single stack ones for others (web server in dual stack and database servers only supporting v4, for example). At this stage, the advantages outlined above on load balancing based on flow labels and Mobile IP mechanisms are applicable to any L3-based mechanism (intra- as well as inter-DC). They will translate into enhanced VM mobility, more effective load balancing, and higher service availability. Furthermore, the simpler integration provided by IPv6 to and from the L2 flat space to the structured L3 one can be applied to achieve simpler deployments, as well as alleviating encapsulation and fragmentation issues when traversing between L2 and L3 spaces. With an appropriate prefix management, automatic address assignment, discovery, and renumbering can be applied not only to public service interfaces, but most notably to data and management paths. Other potential advantages include the application of multicast scopes to limit broadcast floods, and the usage of specific security headers to enhance tenant differentiation. On the other hand, this stage requires a much more careful planning of addressing (please refer to () schemas and access control, according to security levels. While the experimental stage implies relatively few global routable addresses, this one brings the advantages and risks of using different kinds of addresses at each point of the IPv6-aware infrastructure.

An initial approach corresponding to this transition stage relies on taking advantage of specific elements at the aggregation layer described in , and make them able to provide dual-stack gatewaying to the IPv4-based servers and data infrastructure. Typically, firewalls (FW) are deployed as the security edge of the whole service domain and provides safe access control of this service domain from other function domains. In addition, some application optimization based on devices and security devices (e.g. Load Balancers, SSL VPN, IPS and etc.) may be deployed in the aggregation level to alleviate the burden of the server and to guarantee deep security, as shown in . The load balancer (LB) or some other boxes could be upgraded to support the data transmission. There may be two ways to achieve this at the edge of the DC: Encapsulation and NAT. In the encapsulation case, the LB function carries the IPv6 traffic over IPv4 using an encapsulation (IPv6-in-IPv4). In the NAT case, there are already some technologies to solve this problem. For example, DNS and NAT device could be concatenated for IPv4/IPv6 translation if IPv6 host needs to visit IPv4 servers. However, this may require the concatenation of multiple network devices, which means the NAT tables needs to be synchronized at different devices. As described below, a simplified IPv4/IPv6 translation model can be applied, which could be implemented in the LB device. The mapping information of IPv4 and IPv6 will be generated automatically based on the information of the LB. The host IP address will be translated without port translation.

As shown in ,the LB can be considered divided into two parts: The dual-stack part facing the external border, and the IPv4-only part which contains the traditional LB functions. The IPv4 DC is allocated an IPv6 prefix which is for the VSIPv6 (Virtual Service IPv6 Address). We suggest that the IPv6 prefix is not the well-known prefix in order to avoid the IPv4 routings of the services in different DCs spread to the IPv6 network. The VSIPv4 (Virtual Service IPv4 Address) is embedded in VSIPv6 using the allocated IPv6 prefix. In this way, the LB has the stateless IP address mapping between VSIPv6 and VSIPv4, and synchronization is not required between LB and DNS64 server. The dual-stack part of the LB has a private IPv4 address pool. When IPv6 packets arrive, the dual-stack part does the one-on-one SIP (source IP address) mapping (as defined in ) between IPv4 private address and IPv6 SIP. Because there will be too many UDP/TCP sessions between the DC and Internet, the IP addresses binding tables between IPv6 and IPv4 are not session-based, but SIP-based. Thus, the dual-stack part of LB builds IP binding stateful tables for the host IPv6 address and private IPv4 address of the pool. When the following IPv6 packets of the host come from Internet to the LB, the dual stack part does the IP address translation for the packets. Thus, the IPv6 packets were translated to IPv4 packets and sent to the IPv4 only part of the LB.

Another option for deploying a infrastructure at the dual-stack stage would bring dual-stack much closer to the application servers, by requiring hypervisors, VMs and applications in the v6-capable zone of the DC to be able to operate in dual stack. This way, incoming connections would be dealt in a seamless manner, while for outgoing ones an OS-specific replacement for system calls like gethostbyname() and getaddrinfo() would accept a character string (an IPv4 literal, an IPv6 literal, or a domain name) and would return a connected socket or an error message, having executed a happy eyeballs algorithm (). If these hypothetical system call replacements were smart enough, they would allow the transparent interoperation of DCs with different levels of v6 penetration, either horizontal (internal data paths are not migrated, for example) or vertical (per tenant or service group). This approach requires, on the other hand, all the involved DC infrastructure to become dual-stack, as well as some degree of explicit application adaptation.

We can consider a DC infrastructure at the final stage when all network layer elements, including hypervisors, are IPv6-aware and apply it by default. Conversely with the experimental stage, access from the IPv4 Internet is achieved, when required, by protocol translation performed at the edge infrastructure elements, or even supplied by the service provider as an additional network service. There are different drivers that could motivate DC managers to transition to this stage. In principle the scarcity of IPv4 addresses may require to reclaim IPv4 resources from portions of the network infrastructure which no longer need them. Furthermore, the unavailability of IPv4 address would make dual-stack environments not possible anymore and careful assessments will be performed to assess where to use the remaining IPv4 resources. Another important motivation to move DC operations from dual-stack to IPv6-only is to save costs and operational activities that managing a single-stack network could bring in comparison with managing two stacks. Today, besides of learning to manage two different stacks, network and system administrators require to duplicate other tasks such as IP address management, firewalls configuration, system security hardening and monitoring among others. These activities are not just costly for the DC management, they may also lead to configuration errors and security holes. This stage can be also of interest for new deployments willing to apply a fresh start aligned with future IPv6 widespread usage, when a relevant amount of requests are expected to be using IPv6, or to take advantage of any of the potential benefits that an IPv6 support infrastructure can provide. Other, and probably more compelling in many cases, drivers for this stage may be either a lack of enough IPv4 resources (whether private or globally unique) or a need to reclaim IPv4 resources from portions of the network which no longer need them. In these circumstances, a careful evaluation of what still needs to speak IPv4 and what does not will need to happen to ensure judicious use of the remaining IPv4 resources. The potential advantages mentioned for the previous stages (load balancing based on flow labels, mobility mechanisms for transient states in VM or data migration, controlled multicast, and better mapping of L2 flat space on L3 constructs) can be applied at any layer, even especially tailored for individual services. Obviously, the need for a careful planning of address space is even stronger here, though the centralized protocol translation services should reduce the risk of translation errors causing disruptions or security breaches. proposes an approach to a next generation DC deployment, already demonstrated in practice, and claims the advantages of materializing the stage from the beginning, providing some rationale for it based on simplifying the transition process. It relies on stateless NAT64 (, ) to enable access from the IPv4 Internet.

In this section we review some operational considerations related addressing and management issues in V6 DC infrastructure.

There are different considerations related on IPv6 addressing topics in DC. Many of these considerations are already documented in a variety of IETF documents and in general the recommendations and best practices mentioned on them apply in IPv6 DC environments. However we would like to point out some topics that we consider important to mention. The first question that DC managers often have is the type of IPv6 address to use; that is Provider Aggregated (PA), Provider Independent (PI) or Unique Local IPv6 Addresses (ULAs) Related to the use of PA vs. PI, we concur with and that PI provides independence from the ISP and decreases renumbering issues, it may bring up other considerations as a fee for the allocation, a request process and allocation maintenance to the Regional Internet Registry, etc. In this respect, there is not a specific recommendation to use either PI vs. PA as it would depend also on business and management factors rather than pure technical. ULAs should be used only in DC infrastructure that does not require access to the public Internet; such devices may be databases servers, application-servers, and management interfaces of webservers and network devices among others. This practice may decrease the renumbering issues when PA addressing is used, as only public faced devices would require an address change. Also we would like to know that although ULAs may provide some security, the main motivation for its use should be address management. Another topic to discuss is the length of prefixes within the DC. In general we recommend the use of subnets of 64 bits for each vlan or network segment used in the DC. Although subnet with prefixes longer than 64 bits may work, it is necessary that the reader understand that this may break stateless autoconfiguration and at least manual configuration must be employed. For details please read . Address plans should follow the principles of being hierarchical and able to aggregate address space. We recommend at least to have a /48 for each data-center. If the DC provides services that require subassigment of address space we do not offer a single recommendation (i.e. request a /40 prefix from an RIR or ISP and assign /48 prefixes to customers), as this may depend on other no technical factors. Instead we refer the reader to . For point-to-point links please refer to the recommendations in .

Data-centers may use Internet Protocol address management (IPAM) software, provisioning systems and other variety of software to document and operate. It is important that these systems are prepared and possibly modified to support IPv6 in their data models. In general, if IPv6 support for these applications has not been previously done, changes may take sometime as they may be not just adding more space in input fields but also modifying data models and data migration.

Monitoring and logging are critical operations in any network environment and they should be carried at the same level for IPv6 and IPv4. Monitoring and management operations in V6 DC are by no means different than any other IPv6 networks environments. It is important to consider that the collection of information from network devices is orthogonal to the information collected. For example it is possible to collect data from IPv6 MIBs using IPv4 transport. Similarly it is possible to collect IPv6 data generated by Netflow9/IPFIX agents in IPv4 transport. In this way the important issue to address is that agents (i.e. network devices) are able to collect data specific to IPv6. And as final note on monitoring, although IPv6 MIBs are supported by SNMP versions 1 and 2, we recommend to use SNMP version 3 instead.

It is very possible that moving from a single stack data-center infrastructure to any of the IPv6 stages described in this document may incur in capital expenditures. This may include but it is not confined to routers, load-balancers, firewalls and software upgrades among others. However the cost that most concern us is operational. Moving the DC infrastructure operations from a single-stack to a dual-stack may infer in a variety of extra costs such as application development and testing, operational troubleshooting and service deployment. At the same time, this extra cost may be seeing as saving when moving from a dual-stack DC to an IPv6-Only DC. Depending of the complexity of the DC network, provisioning and other factors we estimate that the extra costs (and later savings) may be around between 15 to 20%.

A thorough collection of operational security aspects for IPv6 network is made in . Most of them, with the probable exception of those specific to residential users, are applicable in the environment we consider in this document.

The first important issue that V6 DC managers should be aware is the attacks against Neighbor Discovery Protocol . This attack is similar to ARP attacks in IPv4 but exacerbated by the fact that the common size of an IPv6 subnet is /64. In principle an attacker would be able to fill the Neighbor Cache of the local router and starve its memory and processing resources by sending multiple ND packets requesting information of non-existing hosts. The result would be the inability of the router to respond to ND requests, to update its Neighbor Cache and even to forward packets. The attack does need to be launched with malicious purposes; it could be just the result of bad stack implementation behavior. mentions some options to mitigate the effects of the attacks against NDP. For example filtering unused space, minimizing subnet size when possible, tuning rate limits in the NDP queue and to rely in router vendor implementations to better handle resources and to prioritize NDP requests.

Other important security considerations in V6 DC are related to addressing. Because of the large address space is commonly thought that IPv6 is not vulnerable to reconnaissance techniques such as scanning. Although that may be true to force brute attacks, shows some techniques that may be employed to speed up and improve results in order to discover IPv6 address in a subnet. The use of virtual machines and SLACC aggravate this problem due the fact that they tend to use automatically-generated MAC address well known patterns. To mitigate address-scanning attacks it is recommended to avoid using SLAAC and if used stable privacy-enhanced addresses should be the method of address generation. Also, for manually assigned addresses try to avoid IID low-byte address (i.e. from 0 to 256), IPv4-based addresses and wordy addresses especially for infrastructure without a fully qualified domain name. In spite of the use of manually assigned addresses is the preferred method for V6 DC, SLACC and DHCPv6 may be also used for some special reasons. However we recommend paying special attention to RA and DHCP hijack attacks. In these kinds of attacks the attacker deploys rogue routers sending RA messages or rogue DHCP servers to inject bogus information and possibly to perform a man in the middle attack. In order to mitigate this problem it is necessary to apply some techniques in access switches such as RA-Guard at least. Another topic that we would like to mention related to addressing is the use of ULAs. As we previously mentioned, although ULAs may be used to hide host from the outside world we do not recommend to rely on them as a security tool but better as a tool to make renumbering easier.

In order to avoid being used as a source of amplification attacks is it important to follow the rules of BCP38 on ingress filtering. At the same time it is important to filter-in on the network border all the unicast traffic and routing announcement that should not be routed in the Internet, commonly known as "bogus prefixes".

Finally, let us just emphasize the need for careful configuration of access control rules at the translation points. This latter one is specially sensitive in infrastructures at the dual-stack stage, as the translation points are potentially distributed, and when protocol translation is offered as an external service, since there can be operational mismatches.

None.

We would like to thank Tore Anderson, Wes George, Ray Hunter, Joel Jaeggli, Fred Baker, Lorenzo Colitti, Dan York, Carlos Martinez, Lee Howard, Alejandro Acosta, Alexis Munoz, Nicolas Fiumarelli, Santiago Aggio and Hans Velez for their questions, suggestions, reviews and comments.