BGP Flow Specification for Source Address Validation

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Table of Contents

1. Introduction

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, redirect, and sampling [I-D.huang-savnet-sav-table].¶

There are many mechanisms that can distributely generate SAV rules on routers ([RFC2827], [RFC3704], [RFC5210], [RFC8704], and [manrs-antispoofing]). To facilitate flexible SAV management and improve validation accuracy, centralized SAV rule dissemination is also needed [I-D.li-savnet-intra-domain-architecture][I-D.wu-savnet-inter-domain-architecture], which can be a complementary to existing distributed SAV mechanisms.¶

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 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 flow specification component named Incoming-Interface-Set. SAV rules can be disseminated through BGP FlowSpec by carrying the new flow specification component together with Source Prefix component. Traffic filtering actions of existing BGP FlowSpec can also be carried to specify the actions for the packets failing source address validation.¶

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.¶

2. SAV Rules

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 the packets with invalid source addresses/prefixes, the filtering actions, such as block, rate-limit, and redirect, can be taken [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 Identifier for easy management. Group Identifier is a local interface property on the target routers, and the meaning of it depneds on the configurations of network administrator. Any interface may be associated with one or more Group Identifiers.¶

3. BGP FlowSpec for SAV

SAV can be disseminated to Edge/Border/Aggragation routers (i.e., target 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 has supported source prefix matching and various traffic filtering actions. To dissenimate SAV rules (<source prefix, interface set, validity indicator>), a new flow specification component is needed to carry the information of interface set and validity indicator.¶

    0   1   2   3   4   5   6   7
  +---+---+---+---+---+---+---+---+
  | e | a |  len  | 0 |lt |gt |eq |
  +---+---+---+---+---+---+---+---+

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V|U|     Group Identifier (variable, 6, 14, 30, or 62 bits)    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4. IANA Considerations

This document requests a new entry in "Flow Spec component types registry" with the following values:¶

+=======+========================+===============+
| Type  | IPv4/IPv6 Name         | Reference     |
+=======+========================+===============+
| TBD1  | Incoming-Interface-set | This document |
+-------+------------------------+---------------+

5. Security Considerations

TBD.¶

6. Acknowledgements

Many thanks to the comments from Shunwan Zhuang, Susan Hares, Jeffrey Haas, Mingqing Huang etc.¶

Authors' Addresses