2501 not taking /30 point-point

[saidfrh]

I am trying to configure point-point serial interfaces /30. I have enabled ip classless. After typing the ip address and subnet mask, error message: "Bad mask /30 for address 192.168.3.1". Do you know how I can solve the problem. The other 2501 IOS v. 12 is taking the config. Could the IOS version play a part? Thanks.

Router(config)#hostname routerB

routerB(config)#ip classless

routerB(config)#int s0

routerB(config-if)#ip address 192.168.3.1 255.255.255.252

Bad mask /30 for address 192.168.3.1

routerB(config-if)#

sh ver

1 8133724 c2500-js-l[1].112-26b.bin

[sushilk]

Hi,

It seems that you are using 11.2.26b image. This IOS image is a Deferred Version.

DEFERRAL - IOS Affected

Release Train : 11.2

From : 11.2(26b)

To : 11.2(26c)

Image: : all Platforms

This might be a possible problem for not accepting /30 for point to point link.

Try upgrading to 11.2(26d).

[Kevin Dorrell · Accepted solution]

The subnet you are trying to configure is the first subnet of the major network, the so-called "subnet-zero". It used to be recommended not to use it, especially if you are using classful routing protocols like RIP v1. However, eveyone uses it these days except CCNA exam questions. With earlier version of software, you have to enable it explicitly though with ip subnet-zero.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios112/112cg_cr/5rbook/5rip.htm#xtocid2327393

Kevin Dorrell

Luxembourg

[saidfrh]

Kevin,

Thank you. IP subnet-zero enabled the IP address to work. Since I have not been hired with a CCNA, I am studying to master the CCNP. Do you suggest any book(s) on my journey for mastering CCNP?

Thanks.

Said

[Kevin Dorrell]

The only thing I can really recommend for CCNP is the official CiscoPress CCNP books. If any books are in tune with the curriculum then they should be.

Beware though, CiscoPress books are not perfect, and some contain more errors than others. Study them, read the errata sheets from their web site, and if there is still something that doesn't seem right, post on NetPro. NetPro is a great learning tool.

Do as many labs as you can. The more experience you have, the clearer it becomes.

Good luck, and hope to see CCNP after your name soon.

Kevin Dorrell

Luxembourg

[saidfrh]

Kevin,

Thank you.

Said