Auto-summarizations, discontiguos networks

lildeezul

10.10.10.0

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172.16.10.0

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192.168.10.0

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10.1.1.0
[A] [C]

I believe i get the concept of this summarization, can someone tell me if i am on the correct path.
Thanks

Ok, i think i get it.
So, using contigious networks, like classfull networks, router A only send the 10.0.0.0 update to router B, and router B tells router C about the 10.0.0.0 network, but router C says i already have this network and its directly connected,
but in reality, router C has the 10.1.1.0 network, and Router A has a 10.10.10.0 network, but since a classfull protocol was used Router A, and Router C will only send to classfull network such as 10.0.0.0, right???

if were using OSPF that supports discontigious networks by defualt. then Router A running OSPF will send updates to router B sayin " i know about network 10.10.10.0"
as oposed to 10.0.0.0

Am i correct.??? i belive i understand this.
Also for use of support of discontigous network in EIGRP, then i would have to issue the no summary command. Correct.?????

contigious network dont work in class C address do they??

only in class B and A am i correct??

mikearama

The autosummarization in your scenerio happens on router B, and using a classful routing protocol, will indeed give you problems.

Router B will summarize the 10.10.10.0 network from A to 10.0.0.0 (sending it in updates to Router C), and will also summarize the 10.1.1.0 network from C to 10.0.0.0 (sending that update to Router A).

Now picture Router B's routing table... it will have two paths to the 10.0.0.0/8 network, and assuming they're both 100Mb links, will load balace using both, getting it wrong on average 50% of the time.

So you're right, you'd want to run no auto-summary with any auto-summarizing protocol to prevent B from doing the above.

Oh, and if you're subnetting a class C address into smaller chunks (ie, /25, or /30, or /32), these can be summarized to a class C summary address as well.

Mike