AS Path

An AS Path is a mandatory attribute to set up BGP. It is a sequence of AS numbers through which a network can be accessed. An AS-PATH is a sequence of intermediate AS numbers between source and destination routers that form a directed route for packets to travel. Neighboring autonomous systems (ASes ) use BGP to exchange and update messages about how to reach different AS prefixes. After each router makes a new local decision on the best route to a destination, it will send that route, or path information, along with the accompanying distance metrics and path attributes, to each of its peers. As this information travels through the network, each router along the path prepends its unique AS number to a list of ASes in the BGP message. This list is the route's AS-PATH. An AS-PATH along with an AS prefix, provides a specific handle for a one-way transit route through the network. Use the Configure AS Path page to create, copy and edit autonomous system (AS) path policy objects. You can create AS path objects to use when you are configuring route maps, policy maps, or BGP Neighbor Filtering. An AS path filter allows you to filter the routing update message by using regular expressions.

You can use this object with threat defense devices.

Procedure

Step 1

Select Objects > Object Management and choose AS Path from the table of contents.

Step 2

Click Add AS Path.

Step 3

Enter a name for the AS Path object in the Name field. Valid values are between 1 and 500.

Step 4

Click Add on the New AS Path Object window.

  1. Select the Allow or Block options from the Action drop-down list to indicate redistribution access.

  2. Specify the regular expression that defines the AS path filter in the Regular Expression field.

  3. Click Add.

Step 5

If you want to allow overrides for this object, check the Allow Overrides check box; see Allowing Object Overrides.

Step 6

Click Save.