Clarification on class summarization

Hi,

Just wanted to check in and see if you peeps could clarify and confirm a few things for me.

First of all, can you confirm if I have this correct:

Contiguos Networks would be 11.0.0.0 /8, 12.0.0.0 /8, 13.0.0.0 /8
Because there is no address space in between - 11.0.0.0 --> 11.255.255.255 (BC included)

Discontiguos Networks would be 11.1.1.0 /16, 12.1.1.0 /16, 13.1.1.0 /16
Because there is address space in between - 11.1.1.0, 11.1.2.0, 11.1.3.0...

If there isn't any network address space in between then they can all be summarised, but how would you summarise 11.0.0.0 /8, 12.0.0.0 /8

If there is network address space in between, then they can't (or shouldn't) be summarised, so would you just enter 11.1.1.0 /16, then add 11.1.2.0 /16

Is it also safe to say that if you are using classful routing, then you still have your Class A, B, C networks defined by default masks /8, /16, /24?

If the above is true is it then safe to assume that if using classless routing, that you in affect have no difinitive Class A, B, C networks, because you use the full subnet and subnet mask?

Please could you explain how this would work:
If you have the following addresses:
10.3.1.0 /24
10.3.2.0 /24
10.3.3.0 /24

and you use EIGRP, by default it will just auto-summarize all of these to 10.0.0.0 /8

If this is the case and you also had a 4th network of 10.4.1.0 /24 that this would also be summarised, and would grab all others within the default class A network as well?

Is it also just best to enter 'no auto-summary'?

Sorry it was such a long post, just want to clarify.

Thanks
Nick

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Comments

surfthegecko

please also,..what is meant by classful boundary?
Could this be described with an example please if anybody has the time.

Thanks in advance

Xenz

http://img442.imageshack.us/img442/3026/discont.png

trying to think of the easy way to show you, it may not be fully clear, but discontigous networks is when they networks are seperated like so. the 192.168.2.0/24 network is subnetted, but they're not together as the router on the right is seperated (not contiguous).

http://img91.imageshack.us/img91/1223/boundary.png

Shows a boundary. It's just where the boundary is between networks. You can also imagine summarizing. You would use a summary route to the router on the right for 192.168.2.0/24 because you don't need 4 /26 routes in the table. You can make 1 route to the entire 192.168.2.0/24 network.

EIGRP auto summarization has to do with the network boundary thing above. It doesn't transform routes to the classful boundary like you think it does. When in a situation like the boundary one, it does create a summary route that would be the 10.0.0.0/8 route like you think.

So in the boundary picture above, the router on the right would get a 10.0.0.0/8 summary route (the link between the boundary router and the router on the right is 172.16.x.x). Since auto-summary is on, it will create a summary route for the router on the right.

Classful and classless routing protocols are whether they send their subnet mask and allow VLSM. Classless allow the variable masks. In classful routing you have to use the same mask for all networks i.e /8 /16 /24

**DISCLAIMER** I've been sick for a week, and I'm really tired so take anything I say here as complete lies.

surfthegecko

Cool, I think thats what I was trying to say but through the art of picture

Plus I was using more closely assembled network ranges rather than whole class changes which is probably clearer to see to begin with.

Thanks for this