OSPF wildcard mask

[jtorkos]

I'm curious why the following occurs.

interface e0 172.16.4.1/21

serial s0 172.16.20.1/29

conf t

router ospf 1

network 172.16.4.0 0.0.7.255 area 0

network 172.16.20.0 0.0.0.7 area 0

show run

router ospf 1

network 172.16.0.0 0.0.7.255 area 0

network 172.16.20.0 0.0.0.7 area 0

My question is why don't I see "network 172.16.4.0 0.0.7.255 area 0"?

[n2-goes]

Hello,

if you have 172.16.4.1 255.255.248.0 is part of network 172.16.0.0 255.255.248.0 with the range for hosts from 172.16.0.1 to 172.16.7.254 and broadcast of 172.16.7.255.

Hope this help,

Nadine.

[Harold Ritter]

with 0.0.7.255 will tell OSPF not to care about the 11 last bits of the subnet. The 4 bit is actually part of these 11 last bits.

dec: 172.16.4.0 0.0.7.255

hex: 1010 1100 0001 0000 0000 0100 0000 0000

0000 0000 0000 0000 0000 0111 1111 1111

Hence this bit being ignore and being set to zero when you do a "sh conf".

Hope this helps,

[jtorkos]

Thanks. It makes a bit more sense now.