Wildcard Masks . . . 1

[SnowNinja]

Okay, I know that this is going to sound like a dopey question, but I need to ask;

Is it possible to have a 0.0.0.4 wildcard mask in an ospf scendario? I remember seeing it as a study question, but it doesn't look quite right.

If someone says wilcard mask for 0.0.0.3, it's for a subnet mask of /30 or 255.255.255.252. How would 0.0.0.4 be worded?

Maybe I'm looking at this wrong, but I need to figure this out before the test.

-SnowNinja

 

[Cluebird]

It is an odd wildcard mask but it is valid. In wildcards, the binary zeros are bits to observe while the binary ones are the bits to ignore. You can get very cosmic (WHY?) with wildcards and use them to identify things such as even or odd numbers or particular addresses or some bit pattern that interests you.

I doubt you'll see a 0.0.0.4 wildcard mask on the test.

 

[SnowNinja]

I saw it in the OSPF sim, actually. I was surprised when I saw it. I'm trying to figure out what it was doing there.

-SnowNinja

 

[SnowNinja]

I guess my question is, if someone wanted an OSPF network specified that used a 0.0.0.4, what would the subnet mask number be? Why would "network x.x.x.x 0.0.0.4 area 1" appear in the OSPF config? What subnet mask is being applied that would necessitate a "0.0.0.4" wildcard?

 

[Jsteve]

although this is a valid wildcard, you would never see this is a design. A sim questiion maybe but not production.

Normally you see one of the following:
.3
.7
.15
.31
.63
.127
.255
1.255
3.255
7.255

for a 0.0.0.4 i would guest that the mask would half to be 255.255.255.248 and out of this range you would only be advertising 1 ip address, for example

let's take address 192.168.1.1/29

the range in the last octet would be:
.0 - .7 (with 1-6 being usable addresses)

the wildcard .4 would work like this

00000000* - network
00000001
00000010
00000011
00000100*
00000101
00000110
00000111 - broadcast
_________
00000100 - wilcard

the only thing tha matches is address 192.168.1.4 and the network address.