Nortel Switched Firewall 2.3.3 User’s Guide and Command Reference
100
Open Shortest Path First
213455-L, October 2005
Authentication
OSPF also allows packet authentication and uses IP multicast when sending and receiving
packets. This ensures less processing on routing devices that are not listening to OSPF packets.
Internal versus external routing
To ensure effective processing of network traffic, every routing device on your network needs
to know how to send a packet (directly or indirectly) to any other location/destination in your
network. This is referred to as
internal routing
and can be done with static routes or using
active internal routing protocols, such as OSPF, RIP, or RIPv2.
It is also useful to tell routers outside your network (upstream providers or
peers
) about the
routes you have access to in your network. Sharing of routing information between
autonomous systems is known as
external routing
.
Typically, an AS will have one or more border routers (peer routers that exchange routes with
other OSPF networks) as well as an internal routing system enabling every router in that AS to
reach every other router and destination within that AS.
When a routing device
advertises
routes to boundary routers on other autonomous systems, it
is effectively committing to carry data to the IP space represented in the route being advertised.
For example, if the routing device advertises 192.204.4.0/24, it is declaring that if another
router sends data destined for any address in the 192.204.4.0/24 range, it will carry that data to
its destination.