Defining An As-Path Filter - Dell PowerConnect B-RX Configuration Manual

The <wildcard> parameter specifies the portion of the IP address to match against. The <wildcard>
is a four-part value in dotted-decimal notation (IP address format) consisting of ones and zeros.
Zeros in the mask mean the packet's source address must match the <source-ip>. Ones mean any
value matches. For example, the
<ip-addr> and <wildcard> values 209.157.22.26 0.0.0.255 mean that all hosts in the Class C
subnet 209.157.22.x match the policy.
If you prefer to specify the wildcard (mask value) in Classless Interdomain Routing (CIDR) format,
you can enter a forward slash after the IP address, then enter the number of significant bits in the
mask. For example, you can enter the CIDR equivalent of "209.157.22.26 0.0.0.255" as
"209.157.22.26/24". The CLI automatically converts the CIDR number into the appropriate mask
(where zeros instead of ones are the significant bits) and changes the non-significant portion of the
IP address into zeros. For example, if you specify 209.157.22.26/24 or 209.157.22.26 0.0.0.255,
then save the changes to the startup configuration file, the value appears as 209.157.22.0/24 (if
you have enabled display of subnet lengths) or 209.157.22.0 0.0.0.255 in the startup
configuration file.
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.
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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.
BigIron RX Series Configuration Guide
53-1001986-01
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.
Defining an AS-path filter
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