Brocade Communications Systems ICX 7250 series, Руководство по настройке

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How Multipath load sharing works
Multipath load sharing is performed in round-robin fashion and is based on the destination IP address only. The first time the device
receives a packet destined for a specific IP address, the device uses a round-robin algorithm to select the path that was not used for the
last newly learned destination IP address. Once the device associates a path with a particular destination IP address, the device will
always use that path as long as the device contains the destination IP address in its cache.
NOTE
The device does not perform source routing. The device is concerned only with the paths to the next-hop devices, not the entire
paths to the destination hosts.
A BGP4 destination can be learned from multiple BGP4 neighbors, leading to multiple BGP4 paths to reach the same destination. Each
of the paths may be reachable through multiple IGP paths (multiple OSPF or RIP paths). In this case, the software installs all the multiple
equal-cost paths in the BGP4 route table, up to the maximum number of BGP4 equal-cost paths allowed. The IP load sharing feature
then distributes traffic across the equal-cost paths to the destination.
If an IGP path used by a BGP4 next-hop route path installed in the IP route table changes, then the BGP4 paths and IP paths are
adjusted accordingly. For example, if one of the OSPF paths to reach the BGP4 next hop goes down, the software removes this path
from the BGP4 route table and the IP route table. Similarly, if an additional OSPF path becomes available to reach the BGP4 next-hop
device for a particular destination, the software adds the additional path to the BGP4 route table and the IP route table.
Changing the maximum number of shared BGP4 paths
To change the maximum number of BGP4 shared paths, enter commands such as the following.
device(config)# router bgp
device(config-bgp-router)# maximum-paths 4
device(config-bgp-router)# write memory
Syntax: [no] maximum-paths num | use-load-sharing
The number parameter specifies the maximum number of paths across which the device can balance traffic to a given BGP4 destination.
The number value range is 2 through 8 and the default is 1.
When the use-load-sharing option is used in place of the number variable, the maximum IP ECMP path value is determined solely by
the value configured using the ip load-sharing command.
Customizing BGP4 Multipath load sharing
By default, when BGP4 Multipath load sharing is enabled, both IBGP and EBGP paths are eligible for load sharing, while paths from
different neighboring autonomous systems are not eligible. You can change load sharing to apply only to IBGP or EBGP paths, or to
support load sharing among paths from different neighboring autonomous systems.
To enable load sharing of IBGP paths only, enter the following command at the BGP4 configuration level of the CLI.
device(config-bgp-router)# multipath ibgp
To enable load sharing of EBGP paths only, enter the following command at the BGP4 configuration level of the CLI.
device(config-bgp-router)# multipath ebgp
To enable load sharing of paths from different neighboring autonomous systems, enter the following command at the BGP4
configuration level of the CLI.
device(config-bgp)# multipath multi-as
Syntax: [no] multipath ebgp | ibgp | multi-as
Optional BGP4 configuration tasks
Brocade FastIron Layer 3 Routing Configuration Guide
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