BGP Link-State Extensions for
Seamless BFDHuaweiHuawei Bld., No.156 Beiqing Rd.Beijing100095Chinalizhenbin@huawei.comGoogle, Incaldrin.ietf@gmail.comIndividualjefftant.ietf@gmail.comZTE Corp.gregimirsky@gmail.comHuaweiHuawei Bld., No.156 Beiqing Rd.Beijing100095Chinazhuangshunwan@huawei.com 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, OSPF and OSPFv3) have been extended to advertise the Seamless
BFD (S-BFD) Discriminators.This draft defines extensions to the BGP Link-state address-family to
carry the S-BFD Discriminators information via BGP.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119. 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. defines a mean of advertising one or more
S-BFD Discriminators using the IS-IS Router Capability TLV. defines a new OSPF Router Information (RI) TLV that
allows OSPF routers to flood the S-BFD discriminator values associated
with a target network identifier. This mechanism is applicable to both
OSPFv2 and OSPFv3.The link-state routing protocols (IS-IS, OSPF and OSPFv3) have been
extended to advertise the S-BFD Discriminators. But flooding based
propagation of the S-BFD Discriminators using IGPs is limited by the
perimeter of the IGP domain. For advertising the S-BFD Discriminators
which span across IGP domains (e.g. multiple ASes), the Border Gateway
Protocol (BGP) is better suited as its propagation perimeter is not
limited like the IGPs.This draft defines extensions to the BGP Link-state address-family to
carry the S-BFD Discriminators information via BGP.This memo makes use of the terms defined in .Seamless MPLS extends
the core domain and integrates aggregation and access domains into a
single MPLS domain. In a large network, the core and aggregation
networks can be organized as different autonomous systems. Although the
core and aggregation networks are segmented into different autonomous
systems, but an E2E LSP will be created using hierarchical-labeled BGP
LSPs based on iBGP-labeled unicast within each AS, and eBGP-labeled
unicast to extend the LSP across AS boundaries. Meanwhile, the customer
will see only two service-end points in the Seamless MPLS network. In
order to detect the possible failure quickly and protect the
network/trigger re-routing, BFD MAY be used for the Service Layer (e.g.
for MPLS VPNs, PW ) and the Transport Layer, so the need arises that the
BFD session has to span across AS domain.The link-state routing protocols (IS-IS, OSPF and OSPFv3) have been
extended to advertise the S-BFD Discriminators. But flooding based
propagation of the S-BFD Discriminators using IGPs is limited by the
perimeter of the IGP domain. For advertising the S-BFD Discriminators
which span across IGP domains (e.g. multiple ASes), the Border Gateway
Protocol (BGP) is better suited as its propagation perimeter is not
limited like the IGPs. This draft defines extensions requirement to the
BGP Link-state address-family to carry the S-BFD Discriminators
information via BGP.The BGP-LS NLRI can be a node NLRI, a link NLRI or a prefix NLRI. The
corresponding BGP-LS attribute is a node attribute, a link attribute or
a prefix attribute. BGP-LS defines the TLVs
that map link-state information to BGP-LS NLRI and BGP-LS attribute.
This document adds additional BGP- LS attribute TLVs to encode the S-BFD
Discriminators information. defines the following TLVs to encode the
S-BFD Discriminators information.The ISIS Router CAPABILITY TLV as defined in
will be used to advertise S-BFD discriminators. A new Sub-TLV is defined
as described below. S-BFD Discriminators Sub-TLV is formatted as
specified in .Inclusion of the S-BFD Discriminators sub-TLV in a Router Capability
TLV is optional. Multiple S-BFD Discriminators sub-TLVs MAY be
advertised by an IS. defines the following TLVs to encode the
S-BFD Discriminators information. The format of the S-BFD Discriminator
TLV is as follows:Type - S-BFD Discriminator TLV Type (11)Length - Total length of the discriminator (Value field) in octets,
not including the optional padding. The Length is a multiple of 4
octets, and consequently specifies how many Discriminators are included
in the TLV.Value - S-BFD network target discriminator value or values.Routers that do not recognize the S-BFD Discriminator TLV Type MUST
ignore the TLV. S-BFD discriminator is associated with the BFD Target
Identifier type, which allows de-multiplexing to a specific task or
service.These TLVs are mapped to BGP-LS attribute TLVs in the following way.
The new information in the Link-State NLRIs and attributes is encoded in
Type/Length/Value triplets.The 2 octet Type field values are defined in Table 1. The next 2
octet Length field encodes length of the rest of the TLV. The Value
portion of the TLV is variable and is equal to the corresponding Value
portion of the TLV defined in and .The following 'Node Attribute' TLVs are defined:These TLVs can ONLY be added to the Node Attribute associated with
the Node NLRI that originates the corresponding S-BFD Discriminator
TLV.Existing BGP and BGP-LS operational procedures apply. No new
operation procedures are defined in this document.This document requests assigning code-points from the registry for
BGP-LS attribute TLVs based on table Table 1.Procedures and protocol extensions defined in this document do not
affect the BGP security model. See for
details.The authors would like to thank Nan Wu for his contributions to this
work.