Hi every body!
when i configure the summary route on a router running eigrp, the route appears in routing table as:
D 22.214.171.124 255.255.0 summary address null0.
But when i configure summary route on a router running ripv2, it does not appear so in routing table. Is it normal behavior or it has to do something with my old ios?
thanks a lot!
Correct, thus you don't need a discard route (null0) implemented by the routing protocol as the summary checks for the network to be in the routing table.
A longer prefix is there and that's the one you are summarizing.
Try summarizing 126.96.36.199 255.255.0.0 with your current config.
The null0 implemented within EIGRP during a summarization is called a discard route.
EIGRP allows you to summarize networks that it does not have a route for. For instance, you can send a 0.0.0.0 0.0.0.0 with EIGRP while you can't do this with RIP.
With RIP, in order to summarize a network, the network must be in the RIP database, as soon as the network disappears from the database, the summary will be gone as well - hence there isn't a need for a discard route (null0).
in this case we need to compare info in command reference
nothing explicit here.
To be noted that the route to null0 is a routing loop avoidance mechanism should the packet come back to this router and no specific component route exists for it the local node can silently discard it.
I mean EIGRP has this feature for loop avoidance. (also OSPF has a similar concept in the discard route)
RIP probably doesn't implement this protection but you could use it configuring a manual floating static route to null0
ip route 188.8.131.52 255.255.0 null0 220
the last 220 is the AD
Hope to help