Weighted Load-Balancing over MPLS LSP
50 Router Configuration Guide
If one or more LSP in the ECMP set of a prefix static route does not have a weight configured,
the regular ECMP spraying for the prefix will be performed.
ECMP is also supported when resolving in TTM the same static route with multiple user-
entered indirect next-hops each binding to the same or different tunnel types. The system
picks as many tunnel next-hops as available in RTM beginning from the first indirect next-
hop and up to the value of the ecmp option in the system. In this case, the weighted load-
balancing will be applied directly using the weights of the selected set of tunnel next-hops. If
one or more LSP in the ECMP set of a prefix static route does not have a weight configured,
or if one or more of the indirect next-hops binds to an LDP LSP, the regular ECMP spraying
for the prefix will be performed.
If the same prefix is resolved via both a static route and an IGP shortcut route, then the RTM
default protocol preference will install the static route only. As a result, the set of ECMP
tunnel next-hops and the weighted load balancing behavior will be determined by the static
route configuration and not of the IGP shortcut configuration.
Bi-directional Forwarding Detection
Bi-directional Forwarding Detection (BFD) is a light-weight, low-overhead, short-duration
detection of failures in the path between two systems. If a system stops receiving BFD
messages for a long enough period (based on configuration) it is assumed that a failure along
the path has occurred and the associated protocol or service is notified of the failure.
BFD can provide a mechanism used for liveness detection over any media, at any protocol
layer, with a wide range of detection times and overhead, to avoid a proliferation of different
methods.
SR OS supports asynchronous and on demand modes of BFD in which BFD messages are set
to test the path between systems.
If multiple protocols are running between the same two BFD endpoints then only a single
BFD session is established, and all associated protocols will share the single BFD session.
In addition to the typical asynchronous mode, there is also an echo function defined within
RFC 5880, Bi-directional Forwarding Detection, that allows either of the two systems to
send a sequence of BFD echo packets to the other system, which loops them back within that
system’s forwarding plane. If a number of these echo packets are lost then the BFD session
is declared down.
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