Protocol (BGP) has become a popular choice as a routing protocol in Data Center
(DC) network. The ability to setup Segment Routing-Traffic Engineering (SR-TE)
path initiated by BGP simplifies DC network operation.
for BGP Dynamic Segment Routing Traffic Engineering
Table 1. Feature
Information for BGP Dynamic Segment Routing Traffic Engineering
Segment Routing Traffic Engineering
Cisco IOS XE Amsterdam 17.3.2
In BGP dynamic
SR-TE, the label Switched Path (LSP) is enabled on demand when defined criteria
and policies are met.
commands were introduced or modified:
mpls traffic-eng lsp attributename
Segment Routing –Traffic-Engineering Dynamic BGP
For Anycast SID
support to work BGP-TE should be configured with the prepend feature.
In the case of BGP
Dynamic SR-TE if SR-TE fails, forwarding gets broken.
Segment Routing –Traffic-Engineering Dynamic BGP
In BGP dynamic SR-TE,
the label Switched Path (LSP) is enabled on demand when defined criteria and
policies are met and that is the key difference between manually enabled SR-TE
and BGP dynamic SR-TE. Policies, for example, low latency path, minimum cost
path, and so on are carried via BGP and matches on a given customer prefix.
SR-TE tunnel used for L3VPN or Virtual Private LAN Services (VPLS) using BGP
for auto-discovery and signaling is referred to as BGP-TE Dynamic.
BGP SR-TE dynamic
assumes the on-demand auto-tunnel resides in single IGP domain. In this case
path computation is done via IGP. SR-TE auto-tunnel created based on the
request from BGP is a dynamic SR-TE tunnel. In other words, tunnel path
information, or label stack, is computed based on the BGP next-hop and TE
attribute configuration. BGP dynamic SR-TE functions to trigger an On-demand
LSP (auto-tunnel). The functions include:
prefixes (IPv4 or L3VPN VRF) using communities (community list) via route map
community with a TE attribute-set or profile.
SR-TE profile is
locally configured in attribute-set to define certain SR-TE parameters, for
example, latency, disjoint path and so on. Once the BGP customer prefixes are
mapped to an SR-TE-profile, a tunnel is dynamically created (auto-tunnel or On
demand Label Switched Path (LSP)) using the parameters defined in the
attribute-set, for each specified BGP next-hop and attribute-set pair
associated with the prefixes. A binding SID is associated with each SR-TE
auto-tunnel and passed to BGP. The binding SID or binding label is installed
into Routing Information Base (RIB) and Forwarding Information Base (FIB). FIB
resolves BGP path via the binding SID or binding label, which forwards over the
On demand SR-TE auto-tunnel. The binding-SID is also used to steer the customer
traffic over the SR-TE LSP.
It must be noted that
BGP only carries the SR-TE policy in this case, while path computation is done
via IGP in a single IGP domain. In a single IGP domain the headend node has
full visibility of the end to end path and the topology engineering database
(Traffic Engineering Database or TED). Also it is assumed with BGP Dynamic
SR-TE that all the nodes reside within single AS and single IGP domain.
The above figure
depicts the workflow for BGP-TE dynamic using multiple routing domains use
equipment 2 (CPE) sends BGP update for Prefix-X and adds LL community, for
AC1 announces a
VPN route for prefix X with LL community.
BGP update of the VPN route matching community LL, ToR1 sends a request to PCE
controller for LSP path towards AC1 with low latency TE policy.
element (PCE) controller replies with a label stack, for example, 17003, 1600.
SR-TE auto-tunnel and installs the route for Prefix-X in VRF of this VPN.
TE Label Switched
is used to configure the properties of a LSP. It describes TE profile or policy
such as bandwidth, affinities inclusion and exclusion, links/nodes/SRLG
inclusion and exclusion, metrics, path disjoint degree and group, and so on
that are used to create an auto-tunnel.
How to Configure TE
Label Switched Path Attribute-Set
Configuring TE Label
Switched Path Attribute-Set
You can use the
mpls traffic-eng lsp
<name> to configure TE-LSP attribute. The
following options are available:
Mpls traffic-eng lsp attribute name
affinity Specify attribute flags for links comprising LSP
lockdown Lockdown the LSP--disable reoptimization
priority Specify LSP priority
command can be extended to support configuration for the two options
It can be configured as following:
pce option is set in the TE attribute the dynamic path
is calculated by PCE. Otherwise, the path is calculated locally by TE PCALC
(path-calculation) entity. In the later case, IGP has to be configured and the
BGP next-hop has to be both advertised by IGP and reachable from the local node
over an IGP route.
path-selection metric indicates whether the path
calculation is based on TE metrics or IGP metrics. If this option is not
configured the global value configured under
traffic-eng path-selection metric is used.
path-selection invalidation configures the behavior of
how an LSP reacts to soft failure from network. When an LSP path has a
protected path from IGP against a link or node failure, the failure to the link
or node is considered as soft failure.
path-selection segment-routing adjacency indicates
whether to choose an adjacency-SID with or without IGP protection when
calculating LSP label stack.
disjoint-path indicates the tunnel LSP is a member of disjoint-path
group. Any LSPs within the same disjoint-path group do not traverse the same
resources, such as links, nodes, or SRLG, in its path. This is used to create
two or more tunnel LSPs with disjoint paths.
For BGP-TE Dynamic, a
TE attribute name is associated with a BGP route-map set extension as
match community <name>
set attribute-set <name>
BGP uses the
attribute-set<name> string together with its BGP
next-hop to request a SR-TE auto-tunnel.