Nokia IPSO 4.0 manual BGP AS Path Filtering Example, Aspath Regular Expressions, 448

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7.To configure this filter, enter 10.0.0.0 in New IP prefix to import edit box, and 8 in Mask length edit box; then click Apply.

8.Select Refines in the Match type drop-down list.

This specifies routes that are strictly more specific than 10.0.0.0/8.

9.Finally, click Restrict in the Action field.

This specifies to discard the routes that match this prefix.

10.Click Apply.

The filter is fully configured.

BGP AS Path Filtering Example

BGP updates restrict the routes a router learns or advertises. You can filter these updates based on ASPATH regular expressions, neighbors (AS numbers), or community IDs.

To filter BGP updates based on ASPATH regular expressions, see “To configure route inbound policy on Nokia Platform D based on ASPATH regular expressions.” The following examples, however, give a more detailed description of how to create ASPATH regular expressions.

ASPATH Regular Expressions

1.To accept routes that transit through AS 3662, enter the following ASPATH regular expression in the ASPATH Regular Expression text box:

(.* 3662 .*)

Select Any from the Origin drop-down list; then click Apply.

2.To accept routes whose last autonomous system is 3662, enter this ASPATH regular expression in the ASPATH Regular Expression text box:

(.* 3662)

Select Any from the Origin drop-down list; then click Apply.

3.To accept routes that originated from 2041 and whose last autonomous system is 701, enter the following ASPATH regular expression in the ASPATH Regular Expression text box:

2041 701

Select Any from the Origin drop-down list; then click Apply.

4.To accept SPRINT (AS number 1239) routes that transit through AT&T (AS number 7018) or InternetMCI (AS number 3561), enter the following ASPATH regular expression in the ASPATH Regular Expression text box:

(1239 .* 7018 .*) (1239 .* 3561 .*)

Select Any from the Origin drop-down window.

5.Apply.

6.Click Save to make your changes permanent.

448 Nokia Network Voyager for IPSO 4.0 Reference Guide