Balancing - HP 7102dl - ProCurve Secure Router Configuration Manual

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring BGP
15-100
You can also select routes according to other attributes, such as AS path
or community:
Syntax: match [as-path <listname> | community <listname>]
For example, if your network groups routes into two communities, you
could advertise routes in one of these communities with an artificially
high AS hop count. See "Configuring an AS Path List" on page 15-91 and
"Configuring a Community List" on page 15-90 for instructions on creating
the necessary lists.
3. Next, prepend the hops to selected routes. You can configure the router
to either prepend one or more fictive AS hops to selected routes. Alterna-
tively, you can have the router simply repeat the last AS in a route up to
ten times.
Enter this command:
Syntax: set as-path prepend [last-as <1-10> | <1-65535>]
Use the last-as keyword to have the router re-add the last AS as a new
hop. Specify the number of times that the router should repeat this AS.
You can add a string a fictive AS. For example:
ProCurve(config-route-map)# set as-path prepend 65000 65100
You should consult with your ISP about prepending the AS numbers so
that the fictive AS path does not conflict with route policies that the ISP
router implements.
Setting a Multi-Exit Discriminator Metric for Load Balancing
Another way to influence neighbors to select a certain connection for inbound
traffic is to set different metrics on the routes that you send to different
neighbors. Because BGP prefers routes with a lower metric, the connection
to the neighbor that receives the route with the lowest metric will be more
likely to be selected. (The algorithm BGP uses to select routes relies on many
factors, some of them dependent on configurations on the remote router. You
cannot be sure that the route with the lower metric will actually be selected.)
Because you set the metric to differentiate routes sent over various external
connections, the metric is sometimes called the multi-exit discriminator.