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BigIron RX Series Configuration Guide 751
53-1001810-01
Defining an AS-path filter
26
If you enable the software to display IP subnet masks in CIDR format, the mask is saved in the file
in “/
<mask-bits> ” format. To enable the software to display the CIDR masks, enter the ip
show-subnet-length command at the global CONFIG level of the CLI. You can use the CIDR format
to configure the filter regardless of whether the software is configured to display the masks in CIDR
format.
The <mask> parameter specifies the network mask. If you want the filter to match on all
destination addresses, enter any. The wildcard works the same as described above.
Defining an AS-path filter
To define an AS-path filter, enter the command such as the following.
BigIron RX(config-bgp)# as-path-filter 4 permit 2500
The command defines AS-path filter 4 to permit AS 2500.
Syntax: [no] as-path-filter <num> permit | deny <as-path>
The <num> parameter identifies the filter’s position in the AS-path filter list and can be from 1 –
100. Thus, the AS-path filter list can contain up to 100 filters. The device applies the filters in
numerical order, beginning with the lowest-numbered filter. When a filter match is true, the device
stops and does not continue applying filters from the list.
NOTE
If the filter is referred to by a route map’s match statement, the filter is applied in the order in which
the filter is listed in the match statement.
The permit | deny parameter indicates the action the router takes if the filter match is true.
•
If you specify permit, the router permits the route into the BGP4 table if the filter match is true.
•
If you specify deny, the router denies the route from entering the BGP4 table if the filter match
is true.
The <as-path> parameter indicates the AS-path information. You can enter an exact AS-path string
if you want to filter for a specific value. You also can use regular expressions in the filter string.
Defining a community filter
To define filter 3 to permit routes that have the NO_ADVERTISE community, enter the following
command.
BigIron RX(config-bgp)# community-filter 3 permit no-advertise
Syntax: [no] community-filter <num> permit | deny <num> : <num> | internet | local-as |
no-advertise | no-export
The <num> parameter identifies the filter’s position in the community filter list and can be from 1 –
100. Thus, the community filter list can contain up to 100 filters. The router applies the filters in
numerical order, beginning with the lowest-numbered filter. When a filter match is true, the router
stops and does not continue applying filters from the list.