Bgp shortcuts, Key algorithms – Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) User Manual
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Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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BGP shortcuts
5
NOTE
MPLS cannot be configured on the system globally when a NI-MLX-10Gx8-D card is installed.
The following sections describe some of the procedures and considerations required when
configuring a device to carry IP traffic over an MPLS network:
•
– This feature directs BGP to resolve a route nexthop to a MPLS LSP when one
is available.
•
– This feature allows the user to make selected customer routes
available though LDP created LSP tunnels.
•
“Using traffic-engineered LSPs within an AS”
– This section describes how CoS values are
determined for packets through an LSP.
NOTE
Do not forward packets from one type of tunnel to another type of tunnel in XPP. Packets may not be
routed properly.
BGP shortcuts
In a typical configuration, BGP considers only IP routes when building a routing table. When an
MPLS network uses BGP to propagate routes, BGP must consider whether the MPLS tunnels are
viable routes. The BGP shortcut feature forces BGP to use an MPLS tunnel as the preferred route to
a destination network when one is available. The user can also force BGP to include LSP metrics for
best-route computations.
When configured on an MPLS edge router, BGP computes routes to destinations available through
other edge routers. When BGP determines that a route is available through an edge router that is
reachable through an MPLS tunnel, a BGP shortcut directs BGP to place the MPLS tunnel in the
routing table as the preferred BGP route.
The user can globally enable the BGP shortcut feature and optional inclusion of LSP metrics on a
Brocade device. With the BGP shortcut feature enabled, the Brocade device first attempts to
resolve BGP routes with an MPLS tunnel, and can optionally consider LSP metrics. When the BGP
attempt at route resolution is unsuccessful, the Brocade device defaults to the IPv4 routing table.
Key algorithms
This section describes the behavior of the system in three contexts.
•
Next-hop MPLS disabled: Only IP routing tables are used to resolve routes for the routing table.
•
Next-hop MPLS enabled: LSP with a fixed metric of one is used to resolve the routes. For routes
that cannot be resolved, the system uses the routing table.
•
Next-hop MPLS with LSP metric consideration: When BGP resolves the next hop with LSP, it
uses the LSP metric as the IGP cost for that next hop. When any of the possible paths are
through an LSP, then only LSPs are chosen. The IGP cost of each next hop is then compared,
and only IGP cost paths with the lowest values are considered for ECMP.