rfc-9247

BGP - Link State (BGP-LS) Extensions for Seamless Bidirectional Forwarding Detection (S-BFD)

Z. Li, S. Zhuang, K. Talaulikar (Editor), S. Aldrin, J. Tantsura, G. Mirsky

date2022-06 streamIETF areartg wgidr statusPROPOSED STANDARD pages6 canonicalhttps://www.rfc-editor.org/rfc/rfc9247 doi10.17487/RFC9247

Seamless Bidirectional Forwarding Detection (S-BFD) defines a simplified mechanism to use Bidirectional Forwarding Detection (BFD) with large portions of negotiation aspects eliminated, thus providing benefits such as quick provisioning as well as improved control and flexibility to network nodes initiating the path monitoring. The link-state routing protocols (IS-IS and OSPF) have been extended to advertise the S-BFD Discriminators. This document defines extensions to the BGP - Link State (BGP-LS) address family to carry the S-BFD Discriminators' information via BGP.

Extracted elements (8)

design-rationale §1

S-BFD Discriminators are advertised via BGP-LS because IS-IS and OSPF extensions only distribute discriminators within a single IGP area/level or domain. BGP-LS enables collection and distribution across IGP domains and across multiple Autonomous Systems within an administrative domain, supporting end-to-end S-BFD monitoring for service paths that span IGP boundaries.

bgp, routing

interoperability-note §5

The new TLV augments existing IGP topology information distributed via BGP-LS (RFC 7752). Malformed NLRIs attribute tests defined in RFC 7752 Section 6.2.2 (Fault Management) now encompass the new S-BFD Discriminators TLV.

bgp, routing

interoperability-note §3

The S-BFD Discriminators TLV is derived from protocol-specific advertisements: IS-IS S-BFD Discriminators sub-TLV (RFC 7883) and OSPFv2/OSPFv3 S-BFD Discriminator TLV (RFC 7884). BGP-LS carries the same information that these IGP protocols advertise locally.

bgp, routing

normative-requirement §3 MUST

The Length field of the S-BFD Discriminators TLV MUST be a minimum of 4 octets and increments by 4 octets for each additional discriminator. At least one discriminator MUST be included in the TLV.

bgp, routing

protocol-element §3

RFC 9247 defines a new BGP-LS Attribute TLV called 'S-BFD Discriminators TLV' (Type 1032) for advertising S-BFD Discriminator values as a node-level attribute within the BGP-LS Node NLRI. This enables distribution of S-BFD Discriminators across IGP domains and ASes.

bgp, routing, security

registry §4

IANA permanently allocated TLV code point 1032 for 'S-BFD Discriminators' in the 'BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs' registry. The IS-IS TLV/Sub-TLV column is left empty for this entry.

bgp, registry, routing

security-consideration §6

Advertising S-BFD Discriminators via BGP-LS makes it possible for attackers to initiate S-BFD sessions using the advertised information. The BGP-LS security model requires limiting topology information sharing to trusted entities within an administrative domain, as discussed in RFC 7752 Section 8. Vulnerabilities from exposed discriminators and mitigations are addressed in RFC 7880.

security, bgp, routing

wire-format §3

The S-BFD Discriminators TLV has a 2-octet Type field (value 1032), a 2-octet Length field, and one or more 4-octet Discriminator fields. The Length MUST be a minimum of 4 octets, incrementing by 4 for each additional discriminator.

bgp, routing