eigrp wildcard mask question

[dannan lin]

hi:

i want to know why do we need to use wildcard mask in eigrp .

and if we do not use wildcard masks, will anything go wrong ?

also, if we use normal network masks instead of wildcard mask, does it make any differences?

i run following experiment

i set following network addresses in EIGRP

R1(config-router)# net 170.12.0.0 255.255.255.224

R1(config-router)# net 170.12.0.32 255.255.255.224

R1(config-router)# net 170.12.0.64 255.255.255.224

(i did not use wildcard mask )

on another router , the routing table showed :

D    170.12.0.0/16 [90/20640000] via 192.168.1.1, 00:09:06, Serial2/0

D    172.1.0.0/16 [90/20640000] via 192.168.2.1, 00:10:58, Serial3/0

C    192.168.1.0/24 is directly connected, Serial2/0

C    192.168.2.0/24 is directly connected, Serial3/0

Ok, i see , the addresses were summarised into a class b address.

and then i used wildcard mask

R1(config-router)#net 170.12.0.0 0.0.0.31

R1(config-router)#net 170.12.0.32 0.0.0.31

R1(config-router)#net 170.12.0.64 0.0.0.31

and it had no effects on the routing table of another router

D    170.12.0.0/16 [90/20640000] via 192.168.1.1, 00:02:44, Serial2/0

D    172.1.0.0/16 [90/20640000] via 192.168.2.1, 00:16:06, Serial3/0

C    192.168.1.0/24 is directly connected, Serial2/0

C    192.168.2.0/24 is directly connected, Serial3/0

from above test i see no use of wildcard mask , is there any other test i can do to see the effects of wildcard mask.

thanks in advance.

[nkarpysh]

Hello,

By network command under EIGRP you just specify local interfaces which will participate in EIGRP. It is not affecting/formatting prefixes advertisments. Specifying particular interface ip with wildcard 0.0.0.0 you point that only that interface is enabled in Eigrp with this commands.

But using it this way:

net 170.12.0.0 255.255.255.224

You say any interface on y router with ip like ANY.ANY.ANY.0-224  (if not mistaken in math) should participate in EIGRP. So you enabled almost all of your interfaces for it even those which do not need to run it. So take care!

Nik,

[dannan lin]

thanks guys.

but nik, you said

if i use net 170.12.0.0 255.255.255.224

that means i declear all ip addressed range from  170.12.0.0  - 170.12.0.224 ? is it right ?

[nkarpysh]

Hello

In wild card 0 - means exact macth so smth like 1.2.3.4 0.0.0.0    -- would mean excatly 1.2.3.4

255 in wild card - means any number,

so 1.2.3.4 255.255.255.224 - means ANY.ANY.ANY.4-228 meaning it can be 1.2.3.4, or 192.168.1.16, etc.  So you matching possibly all your interfaces to participate in EIGRP.

Thus net 170.12.0.0 255.255.255.224 for you can mean even macth interface with ip 10.10.10.200 and run EiGRP on it.

Nik,

[cadet alain]

Hi,

you didn't see a difference on the other router because by default EIGRP summarizes at major network boundaries.

just disable auto-summary with no auto-summary command and your netwoks will get advertised with their correct masks.

if you want to experiment with wildcard mask then you'll have to use show ip eigrp interface to see the effect on the local router.

Alain.