supernetting and routing

Dell / D820
April 29, 2010 at 13:20:44
Specs: na, na
Here is my issue:

Cisco 1700/1750 routers
Ran out of class c ips so we are doing a supernet.

Everything works up to the point of changing the lan side of the routers from a /24 to /23 subnet mask. Then we lose the route to the next site.

I don't know why. Everything else works fine.

Thought this was a rip1 issue on the routers so updated to rip2. No change.

Ideas?


See More: supernetting and routing

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#1
April 29, 2010 at 16:13:44
Read the section "Protocol requirements".
http://en.wikipedia.org/wiki/Supernet

The original poster should always write the last response !!!
Let us know, if the problem is solved !!!


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#2
April 29, 2010 at 17:30:30
Please note the comment of upgrading the routers to rip v2 which according to the article does support supernetting.

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#3
April 29, 2010 at 17:55:56
"Then we lose the route to the next site."
Ok, and what is the next side (ip range)?

The original poster should always write the last response !!!
Let us know, if the problem is solved !!!


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Related Solutions

#4
April 29, 2010 at 18:26:29
Are you using Split horizon and poison reverse, to avoid routing loops and poisoned routing entries?

The original poster should always write the last response !!!
Let us know, if the problem is solved !!!


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#5
April 30, 2010 at 07:11:03
hub spoke topology so no chance of routing loops
hub is xxx.xxx.98.0 to .99.255
others are
xxx.xxx..10.x
xxx.xxx..20.x
xxx.xxx..30.x an so forth

Point is that everything works [internal subnet set to /23 and /24] until we change the lan subnet on the routers lan interface at the hub 255.255.255.0 to 255.255.254.0


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#6
April 30, 2010 at 09:11:33
Are the others (xxx.xxx.10.x, xxx.xxx.20.x a.s.o.) also changed to /23?
Because of the other broadcast address.

The original poster should always write the last response !!!
Let us know, if the problem is solved !!!


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#7
April 30, 2010 at 09:51:22
How many networks do you want? With /23 you can only have 2 and it looks like you want 3. If so I would go to /22 subnet or 255.255.252.0 this way you can have 4 networks.

http://bradthemad.org/tech/notes/ci...

P.S.

"Are the others (xxx.xxx.10.x, xxx.xxx.20.x a.s.o.) also changed to /23?
Because of the other broadcast address."

You loss two ip address the x.x.x.0 for network address and x.x.x.255 for broadcast so yes it is also important to know how many nodes you are going to put on these subnets?

http://www.mattjustice.com/ethernet...


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#8
April 30, 2010 at 11:35:59
Point to points are like so

x.x.y.x[lan]<router>[wan]a.a.b.a <ptp> a.a.b.b[wan]<router>[lan]x.x.z.x

What is on either side of the ptp [point to point] doesn't matter as long as its in a subnet not in common with the end points.

In this case x.x.y.x is the supernetted range /23
It is not required to make x.x.z.x /23 since we are not supernetting those sides.

It is only whant the x.x.y.x side of the cisco router lan interface is changed to /23 do we lose the router. At /24 it works fine.
Again everything works in the hub at /23. All remote sites on /24 have no issues getting to and from the servers at /23
Supernetted range of x.x.98.0 to x.x.99.255 work just fine.

Question is that even with Ripv2 which supports supernetting if we change the lan side subnet mask from /24 to /23 it drops the router.

It doesn't make sense to us why it would do this.
Seems reasonable that using the supernetted subnet mask on the lan side of the routers should work at the hub.


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