How ip load sharing works – Brocade TurboIron 24X Series Configuration Guide User Manual
Page 510
476
Brocade TurboIron 24X Series Configuration Guide
53-1003053-01
Configuring IP parameters – Layer 3 Switches
•
IP static route – The value you assign to the metric parameter when you configure the route.
The default metric is 1. Refer to
“Configuring load balancing and redundancy using multiple
static routes to the same destination”
•
RIP – The number of next-hop routers to the destination.
•
OSPF – The Path Cost associated with the path. The paths can come from any combination of
inter-area, intra-area, and external Link State Advertisements (LSAs).
NOTE
If the path is redistributed between two or more of the above sources before entering the IP route
table, the cost can increase during the redistribution due to settings in redistribution filters.
Static route, OSPF load sharing
IP load sharing and load sharing for static routes, OSPF routes, routes are individually configured.
Multiple equal-cost paths for a destination can enter the IP route table only if the source of the
paths is configured to support multiple equal-cost paths.
lists the default and configurable maximum numbers of paths for each IP route source
that can provide equal-cost paths to the IP route table. The table also lists where to find
configuration information for the route source load sharing parameters.
The load sharing state for all the route sources is based on the state of IP load sharing. Since IP
load sharing is enabled by default on all Layer 3 Switches, load sharing for static IP routes, RIP
routes, OSPF routes, and BGP4 routes also is enabled by default.
How IP load sharing works
When the Layer 3 Switch receives traffic for a destination and the IP route table contains multiple,
equal-cost paths to that destination, the device checks the IP forwarding cache for a forwarding
entry for the destination. The IP forwarding cache provides a fast path for forwarding IP traffic,
including load-balanced traffic. The cache contains entries that associate a destination host or
network with a path (next-hop router).
•
If the IP forwarding sharing cache contains a forwarding entry for the destination, the device
uses the entry to forward the traffic.
•
If the IP load forwarding cache does not contain a forwarding entry for the destination, the
software selects a path from among the available equal-cost paths to the destination, then
creates a forwarding entry in the cache based on the calculation. Subsequent traffic for the
same destination uses the forwarding entry.
TABLE 74
Default load sharing parameters for route sources
Route source
Default maximum number of paths
Maximum Number
of paths
See...
TurboIron X Series
Static IP route
4
1
1.
This value depends on the value for IP load sharing, and is not separately
configurable.
8
RIP
4
1
8
OSPF
4
8