Load Balancing - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring BGP
13-98
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.
Follow these steps to set multi-exit discriminators:
1. Divide your network into various destinations for traffic. Divide the
network into as many sections as your organization has connections to
ISP routers. Determine which connections you would like external neigh-
bors to use for traffic destined to the various sections of the network.
Create a separate prefix list to select the set of routes to each section of
the network. For example, you could configure two prefix lists: one that
selects routes to one half of you network and one that selects routes to
the other half.
See "Filtering Advertised Routes According to Network Address" on page
13-90 or "Creating Prefix Lists: Configuring Filters for Route Exchange"
on page 13-78 to learn how to create the necessary lists.
2. You should configure a separate route map for each neighbor to which
your router connects. In each route map, you should configure a separate
route map entry for each set of routes that applies to a section of the
network.
3. First create the route map entry for the set of routes that you want to
advertise as preferable to the first neighbor:
Syntax: route-map <mapname> <sequence number>