I'm studying EIGRP and have come across a few questions regarding summarization.
- From what I'm reading, EIGRP will summarize a network to there classful boundaries when advertising routes by default. From my home lab this doesn't seem to be the case. It seems to show the 172.16.0.0 network with the subnets in the neighbor router B. Parts of the config are below, the next lines describe the topology.
Router_A has a LAN (e0) of 172.16.1.0/24 and is connected to Router_B via a serial connection with 10.1.0.2/16
Router_B has a LAN (e0) of 192.168.1.0/24 and has two serial connections that go to Router_A 10.1.0.1/16 and Router_B 10.2.0.1/16
Router_C has a LAN (e0) of 172.16.2.0/24 and is connected to Router_B via a serial connection 10.2.0.2/16
I thought that the 172.16.1.0/24 and 172.16.2.0/24 networks would show up in Rotuer_B as 172.16.0.0/16 because of the Automatic Summarization? I know that it passes VLSM information but everywhere I read it says that it will summarize be default unless you use the no auto-summary command.
- Also I was reading that when there is a manual summary that it points the interface to NULL0. Why would it do that? Wouldn't that create a bit bucket that would drop all the packets?
- Which leads me to my third question, where it says that the summary is only advertised if a more specific entry is represented in the routing table, what does this mean?
Parts of Config from Router_B in my home lab
router eigrp 1 network 10.1.0.0 0.0.255.255 network 10.2.0.0 0.0.255.255 network 192.168.1.0 auto-summary no eigrp log-neighbor-changes
Router-B#sh protocol Global values: Internet Protocol routing is enabled Ethernet0 is up, line protocol is up Internet address is 192.168.1.30/24 Serial0 is up, line protocol is up Internet address is 10.2.0.1/16 Serial1 is up, line protocol is up Internet address is 10.1.0.1/16 Router-B#sh ip protocol Routing Protocol is "eigrp 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 1 Automatic network summarization is in effect Automatic address summarization: 192.168.1.0/24 for Serial1, Serial0 Maximum path: 4 Routing for Networks: 10.1.0.0/16 10.2.0.0/24 10.2.0.0/16 192.168.1.0 Routing Information Sources: Gateway Distance Last Update 10.1.0.2 90 00:02:23 10.2.0.2 90 00:02:23 Distance: internal 90 external 170
Router-B#sh ip route Gateway of last resort is not set
172.16.0.0/24 is subnetted, 2 subnets D 172.16.1.0 [90/2195456] via 10.1.0.2, 00:10:53, Serial1 D 172.16.2.0 [90/2195456] via 10.2.0.2, 00:02:26, Serial0 10.0.0.0/16 is subnetted, 2 subnets C 10.2.0.0 is directly connected, Serial0 C 10.1.0.0 is directly connected, Serial1 C 192.168.1.0/24 is directly connected, Ethernet0Thanks in advance,
Matt P