Juniper BGP, Configuration Manual

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The tunnel metric can be absolute or relative. An absolute metric indicates there is
no relationship to the underlying IGP cost. A relative metric is added to or subtracted
from the underlying IGP shortest path cost.
Example 1
The following commands announce the tunnel to OSPF and specify a relative metric
of -2:
host1(config-if)# tunnel mpls autoroute announce ospf
host1(config-if)# tunnel mpls autoroute metric relative -2
By default, the LSP is preferred to reach the tunnel endpoint. OSPF will treat this LSP
as having a metric of 2 less than the shortest path metric it has calculated. The LSP
is therefore also preferred over other paths to prefixes beyond the tunnel endpoint.
Example 2
The following commands announce the tunnel to OSPF, specify an absolute metric
of 25, and configure OSPF to enable the consideration of SPF best paths:
host1(config-if)# tunnel mpls autoroute announce ospf
host1(config-if)# tunnel mpls autoroute metric absolute 25
...
host1(config)#
router ospf 1
host1(config-router)# mpls spf-use-any-best-path
OSPF uses this metric in its SPF calculations for traffic to the tunnel endpoint as well
as beyond the endpoint. Traffic is routed through this LSP only when the other
calculated paths have higher metrics.
Configuring the IGPs for Traffic Engineering
For both IGPs, you must issue two commands to enable the IGP to support traffic
engineering.
■
IS-IS—Enable the flooding of MPLS traffic-engineering link information into the
specified IS-IS level with the
mpls traffic-eng command. You must also specify
a stable router interface with the mpls traffic-eng router-id command.
MPLS traffic engineering also requires that IS-IS generate the new-style TLVs that
enable wider metrics. Use the
metric-style wide command to generate the
new-style TLVs. If you are using some IS-IS routers that still cannot interpret the
new-style TLVs, use the
metric-style transition command.
■
OSPF—Enable OSPF areas for traffic engineering with the mpls traffic-eng area
command. OSPF generates opaque LSAs—also known as type-10 opaque link
area link states—to flood the traffic-engineering information to the specified
area. OSPF builds a traffic-engineering database that it uses in the calculation of
shortest path to destinations that satisfy specified traffic-engineering constraints.
As with IS-IS, you must also specify a stable router interface with the
mpls
traffic-eng router-id command.
To enable a multicast network and MPLS traffic engineering (TE) network to
interoperate on a router running OSPF, use the
mpls traffic-eng multicast-intact
command.
Configuring IGPs and MPLS
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Chapter 3: Configuring MPLS