Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual page 150

JUNOSe 11.1.x BGP and MPLS Configuration Guide
The neighbor filter-list commands assign a weight attribute of 1000 to routes passing
through router Boston and a weight attribute of 500 to routes passing through router
NY. Regardless of the origin of the route, routes learned through router Boston are
preferred.
ip as-path access-list
neighbor filter-list
114
Selecting the Best Path
Use to define a BGP access list; use the neighbor filter-list command to apply
a specific access list.
You can apply access list filters on inbound or outbound BGP routes, or both.
You can permit or deny access for a route matching the condition(s) specified
by the regular expression.
If the regular expression matches the representation of the AS path of the route
as an ASCII string, then the permit or deny condition applies.
The AS path allows substring matching. For example, the regular expression 20
matches AS path = 20 and AS path = 100 200 300, because 20 is a substring of
each path. To disable substring matching and constrain matching to only the
specified attribute string, place the underscore (_) metacharacter on both sides
of the string, for example _20_.
The AS path does not contain the local AS number.
Use the no version to remove a single access list entry if permit or deny and a
path-expression are specified. Otherwise, the entire access list is removed.
See ip as-path access-list.
Use to apply an AS-path access list to advertisements inbound from or outbound
to the specified neighbor, or to assign a weight to incoming routes that match
the AS-path access list.
You can specify an optional weight value with the weight keyword to assign a
relative importance to incoming routes matching the AS-path access list.
The name of the access list is a string of up to 32 characters.
You can apply the filter to incoming or outgoing advertisements with the in or
out keywords.
If you specify a BGP peer group by using the peerGroupName argument, all the
members of the peer group inherit the characteristic configured with this
command unless it is overridden for a specific peer. However, you cannot
configure a member of a peer group to override the inherited peer group
characteristic for outbound policy.
New policy values are applied to all routes that are sent (outbound policy) or
received (inbound policy) after you issue the command.
To apply the new policy to routes that are already present in the BGP routing
table, you must use the clear ip bgp command to perform a soft clear or hard
clear of the current BGP session.
Behavior is different for outbound policies configured for peer groups for which
you have enabled Adj-RIBs-Out. If you change the outbound policy for such a
peer group and want to fill the Adj-RIBs-Out table for that peer group with the