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

Protocol Advantages
BGP • ISPs use BGP.
• BGP provides tight control
over which routes are
advertised and accepted.
• Overhead is relatively low.
The administrative distance for a protocol indicates how reliable the router
considers routes discovered by that protocol to be. The lower the administra-
tive distance, the more trusted the route. Table 13-3 shows the default admin-
istrative distance for the various types of routes that the ProCurve Secure
Router can learn.
Table 13-3. Hierarchy of Routes (Most Trusted to Least Trusted)
Type of Route
directly connected
static
BGP
OSPF
RIP v1 and v2

Load Sharing

Typically, a routing table can only include one best route for each destination.
Even if the router learns multiple, equally good routes to the same destination,
it must select one. Other routes cannot be used unless the selected route fails
for some reason. However, the ProCurve Secure Router can also implement
load sharing, which enables it to add multiple routes to the same destination
to its routing table. This option enables the router to use redundant connec-
tions to the same remote site.
When you enable load sharing, the router can place up to six routes to the
same destination in its active routing table. It can learn these routes from any
source—that is, you can enter them manually or the router can learn them
using a dynamic routing protocol. However, keep in mind that load sharing
allows the router to select multiple best routes. The routes must all have the
same metric and administrative distance; otherwise, only the route with the
IP Routing—Configuring RIP, OSPF, BGP, and PBR
Disadvantages
• Configuration is complicated.
• The network must also run an
IGP.
Default Administrative Distance
0
1
• 20 for external routes
• 200 for internal and local routes
110
120
Overview
Uses
• Connecting to an ISP
• Not used over dial-up
connections
13-11