OSFP & wildcard mask

cdad2000

Hey Team,

I'm confused on the different "formats" to config ospf interfaces. Especially, with the wildcard mask portion like when 0.0.0.0 or 255.255.255.255 is used? Is one better then the other??

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Comments

networker050184

One isn't "better" than the other. They are used for two different things. You should revisit your binary basics.

kryolla

0.0.0.0 is the most specific if you only want that one interface partcipating in OSPF and 255.255.255.255 is everything that is up will participate in OSPF.

network 172.16.15.1 0.0.0.0 area 0
network 0.0.0.0 255.255.255.255 area 0

phantasm

As for wildcard bits. If you had a 192.168.2.0 /26 then your mask would be 0.0.63.255 if you only wanted to allow that range of subnets.

I believe that's correct. Someone smack me if it isn't. It's been a long morning at the office. lol.

kryolla

phantasm wrote:

As for wildcard bits. If you had a 192.168.2.0 /26 then your mask would be 0.0.63.255 if you only wanted to allow that range of subnets.

I believe that's correct. Someone smack me if it isn't. It's been a long morning at the office. lol.

/26 is 255.255.255.192 and the inverse mask is 255 minus 192 so it is 0.0.0.63

you might be thinking about /18

phantasm

kryolla wrote:

phantasm wrote:

As for wildcard bits. If you had a 192.168.2.0 /26 then your mask would be 0.0.63.255 if you only wanted to allow that range of subnets.

I believe that's correct. Someone smack me if it isn't. It's been a long morning at the office. lol.

/26 is 255.255.255.192 and the inverse mask is 255 minus 192 so it is 0.0.0.0.63

you might be thinking about /18

it should've been 0.0.0.63. lol. Long morning. Either way if my brainw ould cooperate then your wildcard mask is 1 less of the block size. So with a /26 your block size is 64, your mask bit would be 63.

cdad2000

Great!! So one is more specific on which networks to advertise. 0.0.0.0 is for that one specific interface and 255.255.255.255 advertise everything.

P.S> My subnetting fine, I could VLSM an IPv6 watch ffff:U:BRICK::050184/16

Thanks everybody..else

networker050184

I wasn't trying to be an a$$, my apologies if you took it that way. All I was trying to convey was that it is simple binary to see what the wild card mask matches.

Also, the wildcard mask in the OSPF network statement has nothing to do with your subnet mask. All the network statement does is tell the OSPF process which interface to run on.

cdad2000

050184,

No I was out of line. I apologize as well.

Thanks and take care.

tech-airman

cdad2000 wrote:

Hey Team,

I'm confused on the different "formats" to config ospf interfaces. Especially, with the wildcard mask portion like when 0.0.0.0 or 255.255.255.255 is used? Is one better then the other??

cdad2000,

Do you understand the difference between a multi-access OSPF segment and a non-broadcast multi-access OSPF segment?

Link:

OSPF Design Guide - http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml