IntraSAV - A Solution for Intra-Domain Source Address Validation

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Table of Contents

1. Introduction

The scope of intra-domain SAV is stated in [I-D.ietf-savnet-intra-domain-problem-statement] as follows: "Intra-domain SAV is applied at external interfaces (on routers) facing entities that are not deployed as neighboring ASes and are therefore not covered by inter-domain SAV. For example, an entity can be a single host, a set of hosts, or a customer network with no AS that manages one or more IP prefixes. The entity may source traffic using prefixes assigned by the AS or its own BYOIP prefixes. From the perspective of other ASes, such traffic is originated by the AS."¶

This document specifies a solution, named IntraSAV, for intra-domain source address validation (SAV). This solution addresses the problem stated in the ietf-savnet-intra-domain-problem-statement (RFC-to-be) document.¶

2. IntraSAV Solution

The focus here is on SAV at router interfaces, where traffic sourced from prefixes used (or originated) at the local AS (i.e., the SAV-performing AS) arrives from either (1) directly connected hosts, or (2) customers with non-BGP interfaces [I-D.ietf-savnet-intra-domain-problem-statement]. In these scenarios, the AS may support two types of prefixes for route or traffic origination: (1) its own provider-owned prefixes, and (2) Bring Your Own IP (BYOIP) prefixes. The proposed SAV solution requires BYOIP customers to inform the local AS about the specific prefixes they intend to use on their respective interfaces for routing and/or source addressing. This data becomes part of the configuration information at the local AS (as defined in the Terminology section of [I-D.ietf-savnet-inter-domain-problem-statement]. The local AS similarly incorporates the routing and source addressing requirements (on a per-interface basis) for its own (provider-owned) prefixes into this configuration. Finally, possibly using a SAV agent, the local AS uses the consolidated configuration information to construct and deploy an intra-domain SAV table (allowlist) for each relevant interface of its Customer Edge (CE) routers.¶

The prefix owners (whether the BYOIP customers or the local AS) should register ROAs for their prefixes, authorizing the local AS as the origin. For prefixes originating at the local AS (for either routing or sourcing), the local configuration information takes precedence over the ROA information for both route origination and SAV. However, the local AS should still check the ROAs against its configuration and alert customers to any inconsistencies. This verification is important because remote ASes (one or more hops away) rely on these ROAs (along with other information) to compute their own inter-domain SAV tables [I-D.ietf-savnet-inter-domain-problem-statement] [I-D.ietf-sidrops-bar-sav].¶

The IntraSAV solution method is illustrated below in Figure 1. The figure also illustrates an internal AS topology. IntraSAV is applied at CE routers 1 and 2 on Interfaces 1 and 2 that support Customers 1 and 2, respectively. The Configuration Manager (CM), including a SAV Agent, plays a key role in facilitating IntraSAV. The role of the CM is to authenticate the customers and collect their configuration information for routing and SAV purposes. Customer 1 registers prefixes {p, q} and specifies that both prefixes are routed (i.e., announced). Note that "can be routed (announced)" implies that the prefix can also be used for sourcing traffic. On the other hand, Customer 2 registers prefixes {r, s} and specifies that r is routed while s is not routed but used for sourcing at this AS. The SAV agent in the CM makes use of this configuration information and programs CE router interfaces 1 and 2 with SAV tables (allowlists) {p, q} and {r, s}, respectively. As long as the configuration information available to the local Configuration Manager is complete, IntraSAV guarantees zero improper blocks and zero improper admits.¶

             [ External AS / Internet ]
                        |
+-----------------------------------AS boundary--------+
|                       |                              |
|                 +-------------+                      |
|                 |    ASBR     |                      |
|                 +-------------+                      |
|                       | Interface 3                             |
|                 +-------------+                      |
|                 | Core router |                      |
|                 +-------------+                      |
|                   /         \                        |
|  +-----------------+     +------------------+        |
|  | Customer Edge   |     | Customer Edge    |        |
|  |  CE router 1    |     |  CE router 2     |        |
|  +-----------------+     +------------------+        |
|  Interface 1   /\{p, q}       {r, s}/\  Interface 2  |
|     |           \  SAV tables for   /      |         |
|     |            \   Interfaces 1  /       |         |
|     |             \    and 2      /        |         |
|     |         +-----------------------+    |         |
|     |         | Configuration Manager |    |         |
|     |         |      [SAV Agent]      |    |         |
|     |         +-----------------------+    |         |
|     |            /\ (configuration /\      |         |
|     |            |  information)   |       |         |
+-----|------------|-----------------|-----------------+
      |            |                 |       |
      |            |                 |       |
 Prefixes {p, q}   |                 |  Prefixes {r, s}
   Customer 1 -----+                 +------ Customer 2
 (both p and q are routed)         (r is routed but s is
                                  used only for sourcing)

** To be Discussed (by authors and the WG): The AS operator may choose to apply IntraSAV on Interface 3 at the ASBR in Figure 1. This type of ingress SAV may be done in addition to or as an alternative to doing IntraSAV at the CE router interfaces described above. The important consideration is that the operator should be certain, based on knowledge of the local topology and information in the CM, that all the traffic the ASBR interface receives is expected to be sourced from known prefixes and originating from the local AS. It is clear in the topology of Figure 1 that the expected set of traffic-sourcing prefixes at Interface 3 is equal to the superset of the sets of prefixes configured for the CE router interfaces (Interfaces 1 and 2). So, the operator can confidently apply the prefix-superset {p, q, r, s} as the SAV table (allowlist) on Interface 3 at the ASBR (see Figure 1). It may be noted that this proposal likely goes beyond the scope stated in [I-D.ietf-savnet-intra-domain-problem-statement] except when the ASBR interface in consideration is directly serving a set of hosts or a non-AS customer. Generally, the proposal is useful for cases when the AS operator determines that it is much more feasible to upgrade their ASBR rather than the CE routers for SAV.**¶

3. Security Considerations

Checking configuration information against ROA information helps in affirming accuracy and avoiding improper blocks and improper permits in IntraSAV and at ASes one or more hops away.¶

4. IANA Considerations

This document does not have IANA considerations.¶

5. Acknowledgements

The authors wish to thank Paul Vixie, Doug Montgomery, Jeff Haas, ... for suggestions and discussions.¶

6. References

Authors' Addresses