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New Member

bad mask

hi all im following through a cbtnuggets ospf  lab but it asks to do 7 loopback addresses with the addresses 172.30.0.0-172.30.7.0 sh ip prowith a mask of 255.255.255.0 i know this is a class b add and the default mask is 255.255.0.0,i have done the command ip classless(the command is accepted but in sh run its not displayed,does this mean this ios doesnt support it) but i can not add the /24 mask to the interfaces it says /24 bad mask for 172.30.0.0.how would i get it to accept this mask for those addresses,iknow i could change them to the /16 mask but wanted to stay on the same as the vid to keep things simple.

thanks chris

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Accepted Solutions
Cisco Employee

bad mask

Hi Chris,

Do you add command like this:

ip address 172.30.0.0 255.255.255.0 ? If yes then it is expected .0 (in the end of ip) is not the valid host for that mask. Host portion should be within 1-254. See from my lab

HTTS-C6K1(config-if)#ip addr 172.30.0.0 255.255.255.0

Bad mask /24 for address 172.30.0.0

If you do it like

ip addr 172.30.0.1 255.255.255.0

and see same error - then it is a problem. Send the loegs you see then to check in detail.

Ip classless being default can be invisible on particular platforms so that is ok and I guess not related to the problem.

nik

3 REPLIES
Cisco Employee

bad mask

Hi Chris,

Do you add command like this:

ip address 172.30.0.0 255.255.255.0 ? If yes then it is expected .0 (in the end of ip) is not the valid host for that mask. Host portion should be within 1-254. See from my lab

HTTS-C6K1(config-if)#ip addr 172.30.0.0 255.255.255.0

Bad mask /24 for address 172.30.0.0

If you do it like

ip addr 172.30.0.1 255.255.255.0

and see same error - then it is a problem. Send the loegs you see then to check in detail.

Ip classless being default can be invisible on particular platforms so that is ok and I guess not related to the problem.

nik

New Member

bad mask

thank you i can see it now,in a rush im trying to add the network not the ip,

New Member

tanks for the comment i made

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