Loopback IP address a.b.c.0 (0 on last octet)

[mario_kmc]

Hello all,

I have been doing some IP address planning and whould like the following:

10.24.X.0/24 for some networks

10.24.255.X/32 for the loopbacks of the gateway switch/routers

The networks will start from 10.24.0.0/24 so the first loopback would be 10.24.255.0/32. I did some GNS3 testing and all worked fine. Can I use this 0 (zero) on the last octet with no problem? Is there any case where this can create problems?

I intend to user EIGRP dynamic routing.

Thanks

[Reza Sharifi]

Hi,

You can not use the network address for an interface.  It has to be a host address

So for example you can assign 10.24.255.1/32 to the first router  and 10.24.255.2/32 to the second router and so on.....

HTH

[antonio.guirado]

Hello,

I do not agree. You can use use it as any other only-one-host network (.1/32 .2/32 so on). IOS accepts the command

without problem. EIGRP is a classful protocol and it supports VLSM subnets. So, there are no issues to use it in

Loopback interfaces.

Anyway, Could you explain the Loopback address' purposes?

[mario_kmc]

Hi Antonio,

I believe youmeant classless and not classful.

I'll use the loopback address to reach and manage the switch/routers as they'll have 2/3 L3 links to them. The loopbacks will also be advertised dynamically.

Sent from Cisco Technical Support iPad App

[antonio.guirado]

Hi Mario,

you are right I mean "classless routing protocol". I have used addresses .0 for example in a NAT pool (customers

used a .0 address to go to internet) without problem during 2 years. If you use it to management addresses

I think threre are no issues.

@sjuneay I think you mean "ip subnet-zero" command.

Regards

[mario_kmc]

Hi Antonio,

Thanks for sharing this. It's always good to hear (read) from other's experience. I will actually implement it and hopefully won't get any problems since our devices are all very new.

Sjuneau,

The router is already running classless and allowind subnet-zero yes

[sjuneau]

Hi,

Can you use the command ip classless?  This command works in a router to tell it that the subnets that you define do not follow the different classes of ip address. A class being x.0.0.0 for example 10.0.0.0, B class x.x.0.0, etc.

I did this on routers using eigrp.

HTH