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• Note though no ECMP is performed across both the IP and tunnel next-hops the tunnel end-
point lies in one of the shortest IGP paths for that prefix. In that case, the tunnel next-hop is
always selected as long as the prefix cost using the tunnel is equal or lower than the IGP cost.
The ingress IOM will spray the packets for a prefix over the set of tunnel next-hops and IP next-
hops based on the hashing routine currently supported for IPv4 packets.
Handling of Control Packets
All control plane packets that require an RTM lookup and whose destination is reachable over the
RSVP shortcut will be forwarded over the shortcut. This is because RTM keeps a single route
entry for each prefix unless there is ECMP over different outgoing interfaces.
Interface bound control packets are not impacted by the RSVP shortcut since RSVP LSPs with a
destination address different than the router-id are not included by IGP in its SPF calculation.
Forwarding Adjacency
The forwarding adjacency feature can be enabled independently from the IGP shortcut feature in
CLI. To enable forwarding adjacency, the user enters the following command in IS-IS or OSPF:
•
•
If both rsvp-shortcut and advertise-tunnel-link options are enabled for a given IGP instance,
then the advertise-tunnel-link will win. With this feature, ISIS or OSPF advertises an RSVP LSP
as a link so that other routers in the network can include it in their SPF computations. The RSVP
LSP is advertised as an unnumbered point-to-point link and the link LSP/LSA has no Traffic
Engineering opaque sub-TLVs as per RFC 3906 Calculating Interior Gateway Protocol (IGP)
Routes Over Traffic Engineering Tunnels.
7950 SR OS MPLS Configuration Guide
exclude LSPs with metric higher than underlying IGP cost between the endpoint of
the LSP
prefer tunnel next-hop over ip next-hop
within tunnel next-hops:
i.
select lowest endpoint to destination cost
ii. if same endpoint to destination cost, select lowest endpoint node router-id
iii. if same router-id, select lowest tunnel-index
within ip next-hops:
i.
select lowest downstream router-id
ii. if same downstream router-id, select lowest interface-index
configure>router>isis>advertise-tunnel-link
configure>router>ospf>advertise-tunnel-link
MPLS and RSVP
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