Configuring route reflection parameters, How load sharing affects route selection – Brocade BigIron RX Series Configuration Guide User Manual
Page 945
BigIron RX Series Configuration Guide
867
53-1002484-04
Changing the maximum number of paths for BGP4 load sharing
27
Changing the maximum number of paths for
BGP4 load sharing
Load sharing enables the device to balance traffic to a route across multiple equal-cost paths of
the same type (EBGP or IBGP) for the route.
To configure the device to perform BGP4 load sharing:
•
Enable IP load sharing if it is disabled.
•
Set the maximum number of paths. The default maximum number of BGP4 load sharing paths
is 1, which means no BGP4 load sharing takes place by default. Refer to
maximum number of shared BGP4 paths”
NOTE
The maximum number of BGP4 load sharing paths cannot be greater than the maximum
number of IP load sharing paths.
How load sharing affects route selection
During evaluation of multiple paths to select the best path to a given destination for installment in
the IP route table, the last comparison the device performs is a comparison of the internal paths.
•
When IP load sharing is disabled, the device prefers the path to the router with the lower router
ID if the compare-routerid command is enabled.
•
When IP load sharing and BGP4 load sharing are enabled, the device balances the traffic
across the multiple paths instead of choosing just one path based on router ID.
“How BGP4 selects a path for a route”
on page 816 for a description of the BGP4
algorithm.
When you enable IP load sharing, the device can load balance BGP4 or OSPF routes across up to
four equal paths by default. You can change the number of IP load sharing paths to a value from 2
– 8.
For more information on how load sharing works on the device, refer to
Configuring route reflection parameters
Normally, all the BGP routers within an AS are fully meshed. Each of the routers has an IBGP
session with each of the other BGP routers in the AS. Each IBGP router thus has a route for each of
its IBGP neighbors. For large ASs containing many IBGP routers, the IBGP route information in each
of the fully-meshed IBGP routers can introduce too much administrative overhead.
To avoid this problem, you can hierarchically organize your IGP routers into clusters.
•
A cluster is a group of IGP routers organized into route reflectors and route reflector clients.
You configure the cluster by assigning a cluster ID on the route reflector and identifying the IGP
neighbors that are members of that cluster. All the configuration for route reflection takes
place on the route reflectors. The clients are unaware that they are members of a route
reflection cluster. All members of the cluster must be in the same AS. The cluster ID can be
any number from 1 – 4294967295, or an IP address. The default is the router ID.