Auto Summarization

Hey... confused about auto summary...

If RIPv2 is a Classless Routing protocol.. that means that in addition to the network number, it also sends the subnet mask.... so why then is the no auto-summary still required. The fact that it sends the subnet mask along with the network number should achieve the same goal as the no auto-summary command... shouldn't it?

I am looking at the ICND1 Official Guide 2nd Edition by Odom (on page 440), and he does not use the no auto summary command.... however, even though he does not use no auto summary, there is no auto-summarization happening... I don't get how this is happening...

For those with the book... can you please have a look? This is driving me insane.

Thank you...

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Comments

new2net

billscott92787 wrote: »

I definitely think you aren't understanding what we are trying to say. (I don't mean this in an offensive way). Keep building smaller topologies until it clicks. Your show ip route on the BoundaryRouter is right. That router knows about "ALL ROUTES" it is the "mother" of your topology. So, you configured RIP on all the routers, Boundary, R1, R2, R3, R4, R5, R6. When the boundary router sends it's updates to R4, it says, "Hey, I know about 10.7.7.0 it is going to summarize this in the RIP update that is sent to the router on that network. Are you sure you configured the no auto-summary? It is summarizing that in R6 with the classful subnet mask /8. Are you running RIPv1 or RIPv2? Honestly, I would start with three to four routers. You're topology is too large, I'm not saying you can't understand this, but it's easier to understand if you start with a smaller topology instead of building a larger one like you did, and then trying to understand it. Go back and check your configuration and make sure you configured no auto summary on all the routers..

Initially that is what i did...

I reconstructed your sample topology (and a few small ones like it) and everything works just as I would expect.

This large topology seems to function really weird though... Everytime I reload all the devices (or restart packet tracer), then the boundary router advertises ALL subnets out both interfaces without summarizing... But if i leave Packet Tracer running for 10 mins, then do a show ip route on each side of Boundary Router, the routing tables are just what i expect them to be... i started thinking it might be a problem with packet tracer but im not sure...

BennyLava wrote: »

It looks like you had auto-summary turned off at one point and then re-enabled it.

I thought that too... I thought that in the midst of configuring everything I might have typed no auto-summary by force of habbit, but i checked my configs and they are correct on all routers

billscott92787 wrote: »

I definitely think you aren't understanding what we are trying to say. (I don't mean this in an offensive way). Keep building smaller topologies until it clicks.

i know... i guess all that matters is that it works whenver i created smaller topologies like your Sample Topology. That really helped me understand the concept... I just tried to apply it to a larger scale...

billscott92787

There's no problem with that. I'm not sure why, since it shows them not summarizing the routes when you first load it. PM me your running-config from each router, I'll look at them, or send me the packet tracer file.

billscott92787

I checked your configuration with the "show ip protocols" command on R3 and immediately I got the message, "Automatic network summarization is in effect." So, immediately I confirmed what I figured was going on. You didn't disable auto summary on each router

I disabled it on R3. It still was being summarized. I checked the configuration for R1 and found the same, "Automatic network summarization is in effect." I disabled it. I found that auto summarization was enabled on every single router except R5. That's why you were still getting summarized because you didn't disable it by doing the following

configure terminal
router rip
no auto-summary

After saving the running-config to the startup-config on all the routers, I went around to each router and used the clear ip route * command to clear the routing table. Now look at R3's output for the 99 network.

10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
R 10.0.0.0/8 is possibly down, routing via 99.6.6.1, Serial0/2/0
R 10.1.1.0/24 [120/4] via 99.6.6.1, 00:00:22, Serial0/2/0
R 10.2.2.0/24 [120/3] via 99.6.6.1, 00:00:22, Serial0/2/0
R 10.3.3.0/24 [120/3] via 99.6.6.1, 00:00:22, Serial0/2/0
R 10.4.4.0/24 [120/4] via 99.6.6.1, 00:00:22, Serial0/2/0
R 10.5.5.0/24 [120/3] via 99.6.6.1, 00:00:22, Serial0/2/0
R 10.6.6.0/24 [120/4] via 99.6.6.1, 00:00:22, Serial0/2/0
R 10.7.7.0/24 [120/2] via 99.6.6.1, 00:00:22, Serial0/2/0
99.0.0.0/24 is subnetted, 7 subnets
R 99.1.1.0 [120/1] via 99.6.6.1, 00:00:22, Serial0/2/0
R 99.2.2.0 [120/1] via 99.6.6.1, 00:00:22, Serial0/2/0
R 99.3.3.0 [120/1] via 99.5.5.1, 00:00:13, Serial0/1/0
R 99.4.4.0 [120/1] via 99.6.6.1, 00:00:22, Serial0/2/0
[120/1] via 99.5.5.1, 00:00:13, Serial0/1/0
C 99.5.5.0 is directly connected, Serial0/1/0
C 99.6.6.0 is directly connected, Serial0/2/0
C 99.7.7.0 is directly connected, FastEthernet0/0

R6 was summarizing the route to the 10.0.0 network. Here is its' routing table now

10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
R 10.0.0.0/8 [120/2] via 99.6.6.1, 00:02:49, Serial0/2/0
R 10.1.1.0/24 [120/4] via 99.6.6.1, 00:00:04, Serial0/2/0
R 10.2.2.0/24 [120/3] via 99.6.6.1, 00:00:04, Serial0/2/0
R 10.3.3.0/24 [120/3] via 99.6.6.1, 00:00:04, Serial0/2/0
R 10.4.4.0/24 [120/4] via 99.6.6.1, 00:00:04, Serial0/2/0
R 10.5.5.0/24 [120/3] via 99.6.6.1, 00:00:04, Serial0/2/0
R 10.6.6.0/24 [120/4] via 99.6.6.1, 00:00:04, Serial0/2/0
R 10.7.7.0/24 [120/2] via 99.6.6.1, 00:00:04, Serial0/2/0
99.0.0.0/24 is subnetted, 7 subnets
R 99.1.1.0 [120/1] via 99.6.6.1, 00:00:04, Serial0/2/0
R 99.2.2.0 [120/1] via 99.6.6.1, 00:00:04, Serial0/2/0
R 99.3.3.0 [120/1] via 99.5.5.1, 00:00:23, Serial0/1/0
R 99.4.4.0 [120/1] via 99.6.6.1, 00:00:04, Serial0/2/0
[120/1] via 99.5.5.1, 00:00:23, Serial0/1/0
C 99.5.5.0 is directly connected, Serial0/1/0
C 99.6.6.0 is directly connected, Serial0/2/0
C 99.7.7.0 is directly connected, FastEthernet0/0

Hope this helps

Side Note: you configured your console password and enable password on every router, except the R3, it has the console one but not the enable password

Just in case you wanted to add that in there I figured I'd let you know.

eramos

Really auto summary is in need cause with that like when you used an rip version 2 and eigrp and you have not shut off the auto summary the routing table updates would only includes an ip classful

example: 172.31.3.0/24 (network) in routing table it will be updated as: 172.31.0.0/16 only due that it is a class b(classful) with that no specific which netwrk address would received it for example you have lots of net addresses such as 172.31.1.0, 172.31.2.0 , and 172.31.3.0. when automatic summarization is "off" the route will not summarize all the subnets who has the sme network with classful consideration and you will see that these message nor traffic is for 172.31.3.0 only.

meaning, after no auto-summary is in effect it will be inputed like these:
172.31.3.0 instead of 172.31.0.0