| Internet-Draft | BGP FlowSpec for SAV | February 2024 |
| Geng & Li | Expires 20 August 2024 | [Page] |
BGP FlowSpec reuses BGP route to distribute infrastructure and propogates traffic flow information with filtering actions. This document specifies a new BGP extended community named Source Address Validation (SAV) Interface-set to disseminate SAV rules through BGP FlowSpec.¶
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Source Address Validation (SAV) is an efficient method for preventing source address spoofing-based attacks. SAV rules indicate the valid/invalid incoming interfaces of a specific source IP address or source IP prefix. The rules can be deployed on edge routers, border routers, or aggregation routers for checking the validity of intra-domain and inter-domain packets. For invalid packets, filtering actions can be taken such as block, rate-limit, and redirect. There are many mechanisms that can generate SAV rules on routers ([RFC2827], [RFC3704], [RFC5210], [RFC8704], and [manrs-antispoofing]). However, the challenges of accurate validation and operation exist in asymetric routing scenarios or dynamic networks [I-D.ietf-savnet-intra-domain-problem-statement][I-D.ietf-savnet-inter-domain-problem-statement]. To facilitate SAV management, additional SAV rule dissemination is needed [I-D.li-savnet-intra-domain-architecture][I-D.wu-savnet-inter-domain-architecture].¶
BGP FlowSpec is a convenient and flexible tool for traffic filtering/controling ([RFC8955], [RFC8956]). It propogates traffic flow information for different traffic control purposes through the BGP protocol extension. Existing BGP FlowSpec design has supported source prefix matching and various traffic filtering actions but does not support binding valid/invalid incoming interfaces to source prefixes. With a minor extension, BGP FlowSpec can be used for SAV rule dissemination.¶
This document specifies a new BGP extended community named SAV Interface-set extended community. SAV rules can be disseminated through BGP FlowSpec by combining the new extended community with source prefix component and filtering actions of existing BGP FlowSpec. The new extension can be used to configure SAV rules on remote routers. It can also act as a supplement of existing SAV mechanisms and help improve SAV accuracy.¶
SAV: Source address validation¶
SAV Rule: The rule that indicates the valid/invalid incoming interfaces of a specific source IP address or source IP prefix.¶
AS: Autonomous System¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
SAV rules can be used for checking the validity of source addresses of incoming packets. A rule usually has a format of <source prefix, interface set, validity indicator>. source prefix is for matching specific packets. Interface set represents a set of physical interfaces from which the packets arrive. Validity indicator indicates whether the packets matching the source prefix and arrival interface are valid or invalid. So, validity indicator has a value of either valid or invalid. For example, the rule <P1, [intf1, intf2], valid> means the source prefix P1 must arrive the router at interface Intf1 or Intf2, otherwise, P1 is invalid. For invalid source prefixes, the filtering actions, such as block, rate-limit, and redirect, can be taken on the packets [I-D.huang-savnet-sav-table].¶
In real networks, the interface set in SAV rules usually can be grouped. For example, the interfaces can be grouped as:¶
Subnet interface set that contains the interfaces connecting a target subnet.¶
All customer AS interfaces set or the customer AS interfaces set of a customer AS.¶
All lateral peer AS interfaces set or the lateral peer AS interfaces set of a lateral peer AS.¶
All transit provider AS interfaces set or the transit provider AS interfaces set of a transit provider AS.¶
These interface set can be indentified by a group id for easy management.¶
SAV can be disseminated to Edge/Border/Aggragation routers through BGP FlowSpec, as shown in the figure below. The controller is used to set up BGP connection with the routers in a SAV-deployed AS or domain. Note that, SAV rules disseminated by BGP FlowSpec can take effect alone or acts as a management tool of other SAV mechanisms (e.g., [RFC8704]).¶
+------------+
| Controller |
+------------+
/ | \
/ FS | FS \ FS
/ | \
+-------------+ +--------------+ +---------+
| Provider or | | SAV-deployed | | |
| Customer or |------# AS/Domain #------| Subnets |
| Peer AS | | | | |
+-------------+ +--------------+ +---------+
¶
Existing BGP FlowSpec supports the component for matching source prefix and various filtering actions. This document will define a new extended community called SAV Interface-set extended community, whose design follows [I-D.ietf-idr-flowspec-interfaceset]. SAV rules can be disseminated through BGP FlowSpec by combining the new extended community with source prefix component and filtering actions of existing BGP FlowSpec ([RFC8955], [RFC8956]).¶
The newly defined SAV Interface-set extended community is encoded as follows:¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | SubType | AS Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AS Number (cont.) |U|V| Group Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
The meaning of fields:¶
Type (1 octect): 0x07 or 0x47. The value of 0x07 is for FlowSpec Transitive Extended Communities, and 0x47 represents FlowSpec Non-Transitive Extended Communities. The two values have been allocated by IANA [I-D.ietf-idr-flowspec-interfaceset].¶
SubType (1 octect): TBD. SubType field indicates SAV Interface-set extended community.¶
AS Number (4 octects): Four-octect AS number. This field indicates the target AS where the SAV rule takes effect.¶
Group Identifier (14 bits): A 14-bit number with the value ranging within 0..16383. Group identifier is a local property and identifies a set of interfaces for the source prefix carried in NLRI. The meaning of a group identifier depends on the configuration of network administrator. An interface is usually associated with one group identifiers.¶
Flag V (1 bit): 1 means the identified interface set is valid for the source prefix, while 0 means the interface set is invalid for the source prefix.¶
Flag U (1 bit): 1 means the rest of interfaces (not included in the interface set) on the local router are unknown for the source prefix. 0 means the rest of interfaces on the local router are invalid (when V=1) or valid (when V=0) for the source prefix.¶
In a BGP update, there may be more than one instances of SAV Interface-set extended community. The final interface set for the corresponding source prefix MUST be the union of these instances.¶
Multiple source prefixes can be put in multiple BGP FlowSpec NLRIs of one BGP update. In such case, these source prefixes MUST share the same SAV Interface-set extended communities.¶
Example 1: Configure soucre prefix P1 as valid at AS1's interfaces (Group Identifier=ID1) connecting a multi-homed subnet.¶
Encoding description: NLRI carries source prefix P1 following existing BGP FlowSpec. The SAV Interface-set community with Type=0x07 and subType=TBD carries ID1 with AS number=AS1, flag V=1, and U=1.¶
Example 2: Block soucre prefix P2 at AS2's interfaces (Group Identifier=ID2) connecting to transit providers.¶
Encoding description: NLRI carries source prefix P2 and BGP extended community carries the drop action (e.g., set traffic-rate-bytes to zero). The SAV Interface-set community with Type=0x07 and subType=TBD carries ID2 with AS number=AS2, flag V=0 and U=1.¶
This document requests a new subtype (suggested value 0x03) within the FlowSpec Transitive Extended Communities (0x07) and FlowSpec Non-Transitive Extended Communities (0x47). This sub-type shall be named "SAV Interface-set", with a reference to this document.¶
+=======+======================+===============+ | Value | Name | Reference | +=======+======================+===============+ | TBD | SAV Interface-set | This document | +-------+----------------------+---------------+¶
No new security issues are introduced.¶
Many thanks to the comments from Shunwan Zhuang.¶