Defining Filtering Lists - 3Com Switch 4800G 24-Port Configuration Manual

490 C 37: R
HAPTER OUTING
Routing Policy
Application

Defining Filtering Lists

Prerequisites
P C
OLICY ONFIGURATION
AS-path
AS path is only applicable to IPv6 BGP. There is an AS-path field in the IPv6 BGP
packet. An AS path list specifies matching conditions according to the AS-path
field.
Community list
Community list only applies to IPv6 BGP. The IPv6 BGP packet contains a
community attribute field to identify a community. A community list specifies
matching conditions based on the community attribute.
Extended community list
Extended community list (extcommunity-list) applies to IPv6 BGP only. It is used for
Route-Target extcommunity for VPN.
Routing policy
A routing policy is used to match against some attributes in given routing
information and modify the attributes of the information if match conditions are
satisfied. It can reference the above mentioned filters to define its own match
criteria.
A routing policy can comprise multiple nodes, which are in logic OR relationship.
Each node is a match unit, and the system compares each node to a packet in the
order of node sequence number. Once a node is matched, the routing policy is
passed and the packet will not go through the next node.
Each node comprises a set of if-match and apply clauses. The if-match clauses
define the match criteria. The matching objects are some attributes of routing
information. The different if-match clauses on a node is in logical AND
relationship. Only when the matching conditions specified by all the if-match
clauses on the node are satisfied, can routing information pass the node. The
apply clauses specify the actions to be performed after the node is passed,
concerning the attribute settings for routing information.
A routing policy is applied in two ways:
When redistributing routes from other routing protocols, a routing protocol
■
accepts only routes passing the routing policy.
When receiving or advertising routing information, a routing protocol uses the
■
routing policy to filter routing information.
Before configuring this task, you need to decide on:
IP-prefix list name
■
Matching address range
■
Extcommunity list sequence number
■