CHAPTER 8
Implementing UCMP
The unequal cost multipath (UCMP) load-balancing provides the capability to load balance traffic proportionally
across multiple paths, with different cost. Generally, higher bandwidth paths have lower Interior Gateway
Protocol (IGP) metrics configured, so that they form the shortest IGP paths.
With the UCMP load-balancing enabled, protocols can use even lower bandwidth paths or higher cost paths
for traffic, and can install these paths to the forwarding information base (FIB). These protocols still install
multiple paths to the same destination in FIB, but each path will have a 'load metric/weight' associated with
it. FIB uses this load metric/weight to decide the amount of traffic that needs to be sent on a higher bandwidth
path and the amount of traffic that needs to be sent on a lower bandwidth path.
In the following example, there are 3 paths to get to Network X as follows:
Figure 7: Topology for UCMP
Cost from Router E to Net -XPaths
40E-B-A
50E-C-A
40E-D-A
Routing Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x
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