Filtering, Filtering as-paths, How load sharing affects route selection – Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) User Manual
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Brocade Virtual ADX Switch and Router Guide
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Filtering
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To configure the device to perform BGP4 load sharing:
•
Enable IP load sharing if it is disabled.
•
Set the maximum number of BGP4 load sharing paths. The default maximum number is 1,
which means no BGP4 load sharing takes place by default. Refer to
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 device performs a final comparison of the internal paths. The following
events occur when load sharing is enabled or disabled:
•
When load sharing is disabled, the device prefers the path with the lower device ID if the
compare-routerid command is enabled.
•
When load sharing and BGP4 load sharing are enabled, the device balances the traffic across
multiple paths instead of choosing just one path based on device ID.
“How BGP4 selects a path for a route”
on page 200 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 load sharing paths to a value from 2 – 8.
Filtering
This section describes how to configure filters for AS-paths, communities, and other BGP4
attributes.
Filtering AS-paths
You can filter updates received from BGP4 neighbors based on the contents of the AS-path list
accompanying the updates. For example, to deny routes that have the AS 10.3.2.1 in the AS-path
from entering the BGP4 route table, you can define a filter.
The device provides the following methods for filtering on AS-path information:
•
•
AS-path ACLs
NOTE
The device cannot support AS-path filters and AS-path ACLs at the same time. Use one method or
the other, but do not mix methods.
NOTE
Once you define a filter or ACL, the default action for updates that do not match a filter is deny. To
change the default action to permit, configure the last filter or ACL as permit any.