3Com Switch 7754, Configuration Manual

Page: 377 / 940

37
IP R
OUTING
P
OLICY
C
ONFIGURATION
IP Routing Policy
Overview
When a router distributes or receives routing information, it may need to
implement some policies to filter the routing information, so as to receive or
distribute only the routing information meeting given conditions. A routing
protocol (RIP, for example) may need to import the routing information discovered
by other protocols to enrich its routing knowledge. While importing routing
information from another protocol, it possibly only needs to import the routes
meeting given conditions and set some attributes of the imported routes to make
the routes meet the requirements of this protocol.
For the implementation of a routing policy, you need to define a set of matching
rules by specifying the characteristics of the routing information to be filtered. You
can set the rules based on such attributes as destination address and source
address of the information. The matching rules can be set in advance and then
used in the routing policies to advertise, receive, and import routes.
Filters The Switch 7750 provide five kinds of filters (route-policy, ACL, AS-path,
community-list and ip-prefix) that can be referenced by routing protocols. The
following sections describe these filters.
Route-policy
A route-policy is used to match some attributes with given routing information
and the attributes of the information will be set if the conditions are satisfied.
A route policy can comprise multiple nodes. Each node is a unit for matching test,
and the nodes will be matched in the order of their node numbers. Each node
comprises a set of
if-match and apply statements. The if-match statements
define the matching rules. The matching objects are some attributes of routing
information. The relationship among the
if-match statements for a node is
“AND”. As a result, a matching test against a node is successful only when all the
matching conditions specified by the
if-match statements in the node are
satisfied. The apply statements specify the actions performed after a matching
test against the node is successful, and the actions can be the attribute settings of
routing information.
The relationships among different nodes in a route-policy are “OR”. As a result,
the system examines the nodes in the route-policy in sequence, and once the
route passes a node in the route-policy, it will pass the matching test of the
route-policy without entering the test of the next node.
ACL
Normally, a basic ACL is used to filter routing information. You can specify a range
of IP addresses or subnets when defining a basic ACL so as to match the