SR Policies for
Path Segment and Bi-directional Path in BGP-LSHuawei TechnologiesHuawei Campus, No. 156 Beiqing Rd.Beijing100095Chinachengli13@huawei.comHuawei TechnologiesHuawei Campus, No. 156 Beiqing Rd.Beijing100095ChinaMach.chen@huawei.comHuawei TechnologiesHuawei Campus, No. 156 Beiqing Rd.Beijing100095Chinajie.dong@huawei.comHuawei TechnologiesHuawei Campus, No. 156 Beiqing Rd.Beijing100095Chinalizhenbin@huawei.com
Routing Area
Interdomain Routing Working GroupThis document specifies the way of collecting configuration and
states of SR policies carrying path ID and bi-directional path
information by using BPG-LS. Such information can be used by external
conponents for many use cases such as performance measurement, path
re-optimization and end-to-end protection.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.Segment routing (SR)
is a source routing paradigm that allows the ingress node steers packets
into a specific path according to the Segment Routing Policy . However, the SR Policies defined in only supports
uni-directional SR paths and there is no path ID in a Segment List to
identify an SR path. For identifying an SR path and supporting
bi-directional path ,
new policies carrying Path ID and bi-directional path information are
defined in , as well as
the extensions to BGP to distribute new SR policies. The path ID can be
a path segment in SR-MPLS , or a path ID in SRv6
, or other IDs that
can identify a path. In many network scenarios, the configuration and state of each TE
Policy is required by a controller which allows the network operator to
optimize several functions and operations through the use of a
controller aware of both topology and state information . To collect the TE Policy information that is locally available in a
router, describes a
new mechanism by using BGP-LS update messages. Based on the mechanism defined in , this document describes a
mechanism to distribute configuration and states of the new SR policies
defined in to external
components using BGP-LS. This memo makes use of the terms defined in and .A mechanism to collect states of SR Policies via BGP-LS is proposed
by . The
characteristics of an SR policy can be described by a TE Policy State
TLV, which is carried in the optional non-transitive BGP Attribute
"LINK_STATE Attribute" defined in . The TE
Policy State TLV contains several sub-TLVs such as SR TE Policy
sub-TLVs. Rather than replicating SR TE Policy sub-TLVs, reuses the equivalent
sub-TLVs as defined in .As defined in , the new SR
policies for bi-directional path has the following format:For collecting configuration and states of uni-directional and
bi-directional SR policies defined in , new sub-TLVs
in SR TE Policy sub-TLVs should be defined. Likewise, rather than
replicating SR Policy sub-TLVs, this document can reuse the equivalent
sub-TLVs as defined in .This section defines an SR Path ID sub-TLV to specify an SR path,
and it is included in the Segment List sub-TLV as defined in .An SR Path ID sub-TLV is associated with an SR path specified by a
Segment List sub-TLV, and it MUST appear only once within a Segment
List sub-TLV. It has the following format:All fields, including type and length, are defined in .In some scenarios like mobile backhaul transport network, there are
requirements to support bi-directional path. In SR, a bi-directional
path can be represented as a binding of two uni-directional SR paths
. defines new
sub-TLVs to describe an SR bi-directional path. An SR policy carrying
SR bi-directional path information is expressed in Figure 1. This section defines an SR bi-directional path sub-TLV to specify
a bi-directional path, which contains a Segment List sub-TLV and an associated
Reverse Path Segment List as defined in . The SR
bi-directional path sub-TLV has the following format:All fields, including type and length, are defined in .This section defines an SR Reverse Path Segment List sub-TLV to
specify an SR reverse path associated with the path specified by the
Segment List in the same SR Bi-directional Path Sub-TLV, and it has
the following format:All fields, including type and length, are defined in
.No new operation procedures are defined in this document, the
operations procedures of can apply to this
document.Typically but not limited to, the uni/bi-directional SR policies
carrying path identification information can be distributed by the
ingress node.Generally, BGP-LS is used for collecting link states and
synchronizing with the external component. The consumer of the
uni/bi-directional SR policies carrying path identification information
is not BGP LS process by itself, and it can be any applications such as
performance measurement and path re-coputation or re-optimization, etc.
The operation of sending information to other precesses is out of scope
of this document.TBATBATBA