Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 76)

with a given cost for a given destination, the BGP4 route table cannot contain equal-cost paths to the
destination. Consequently, the IP route table will not receive multiple equal-cost paths from BGP4.
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 BrocadeLayer 3 switches, load sharing for static IP routes, RIP
routes, OSPF routes, and BGP4 routes also is enabled by default.
Default load sharing parameters for route sources TABLE 7
Route source Default maximum
number of paths Maximum number of paths
FSX FCX / ICX 6450 / ICX 6610 / ICX
6650 / ICX 7750
Static IP route 4 1 6 1 8 1
RIP 4 1 6 1 8 1
OSPF 4 6 8
BGP4 1 4 4
1 This value depends on the value for IP load sharing, and is not separately configurable.
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.
Response to path state changes
If one of the load-balanced paths to a cached destination becomes unavailable, or the IP route table
receives a new equal-cost path to a cached destination, the software removes the unavailable path
from the IP route table. Then the software selects a new path. Disabling or re-enabling load sharing
To disable IP load sharing, enter the following commands.
device(config)# no ip load-sharing
Syntax: no ip load-sharing
How IP load sharing works
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