HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 622

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Overview
13-8
What information routers include in routing updates—With some routing
protocols, routers exchange their entire routing tables. With other routing
protocols, routers exchange only portions of the routing table. Routers
that are running a link-state protocol, such as OSPF, do not exchange
actual routes. Instead, these routers exchange information about their
links. Each router then uses this information to generate a network
topology and calculates its own best routes according to this topology. In
addition, some routing protocols allow routers to generate route
summarizations or summary routes, which advertise an entire range of
networks in a single entry in the routing update.
Which routers and router interfaces send and receive updates—Most
protocols specify that when routers receive an update on an interface,
they do not send the same update from that interface. This common sense
rule minimizes overhead. Some routing protocols also cut down on pack-
ets circulating through the network by assigning different routers differ-
ent roles. For example, only the designated router (DR) in an OSPF subnet
floods link-state advertisements (LSAs) to other routers in the subnet, and
only area border routers (ABRs) store information about the entire AS. If
you understand the role of each router in your WAN, you can configure
routers to minimize congestion.
When routers send and receive updates and hellos—To lower overhead
and conserve bandwidth, you can alter how often routers send certain
messages.
You can fine tune the routing protocol to best fit your router's role in your
network topology. Some protocols provide more flexibility in implementation
than others. In general, OSPF and BGP provide more options for customizing
advertisements for your particular network environment. However, the con-
figuration for these protocols can be more complex than the configuration
for RIP.
Before you implement a routing protocol on your network, you should evalu-
ate the options each protocol provides and then determine which one will
work best for your network environment. Table 13-1 compares how RIP, OSPF,
and BGP control basic options. You can learn about each protocol in more
detail in the overview for the configuration section on that protocol.