Default Route Ecmp - Dell PowerConnect B-RX Configuration Manual

7
Configuring forwarding parameters
TABLE 48
Route source
OSPF
BGP4
How IP load sharing works
On the device, IP load sharing (also known as ECMP load sharing) is done by the hardware. If there
is more than one path to a given destination, a hash is calculated based on the source MAC
address, destination MAC address, source IP address, destination IP address, and IP protocol. This
hash is used to select one of the paths.
Changing the maximum number of load sharing paths
By default, IP load sharing allows IP traffic to be balanced across up to four equal path. You can
change the maximum number of paths that the device supports to a value of 2 – 8.
For optimal results, set the maximum number of paths to a value equal to or greater than the
maximum number of equal-cost paths that your network typically contains. For example, if the
device has six next-hop routers, set the maximum paths value to six.
NOTE
If the setting for the maximum number of paths is lower than the actual number of equal-cost paths,
the software does not use all the paths for load sharing.
To change the number of paths, enter a command such as the following.
BigIron RX(config)# ip load-sharing 8
Syntax: [no] ip load-sharing [<number>]
Enter a value from 2 – 8 for <number> to set the maximum number of paths.
Response to path state changes
If one of the load-balanced paths becomes unavailable, the IP route table in hardware is modified
to stop using the unavailable path. The traffic is load balanced between the available paths using
the same hashing mechanism described above. (Refer to
page 204.)

Default route ECMP

On the BigIron RX, IP load sharing (also known as ECMP load sharing) is done by the hardware. If
there is more than one path to a given destination, a hash is calculated based on the source MAC
address, destination MAC address, source IP address, destination IP address, and IP protocol. This
hash is used to select one of the paths.
If there are multiple next-hop routers for the default route in the IPv4 routing table, routed packets
on the default route would be automatically load-balanced among these next-hops through a
hashing formula, calculated based on (IPv4 Destination Address, IPv4 Source Address, IPv4 Source
Port, IPv4 Destination Port, DA-MAC, and SA-MAC) of the packets received. This feature allows for
load distribution of traffic among the available default route next-hops.
204
Default load sharing parameters for route sources (Continued)
Default maximum number of paths
4
1
Maximum number of paths
8
4
"How IP load sharing works"
BigIron RX Series Configuration Guide
See...
page 204
page 789
on
53-1001810-01