Wild Card Mask

I have  R1 that has learned EIGRP routes from R2  as shown below.



R1(config-std-nacl)#do sh ip route                
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, + - replicated route

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 7 subnets, 7 masks
D        10.1.0.0/16 [90/156160] via 192.168.12.2, 00:00:08, FastEthernet0/0
D        10.2.0.0/17 [90/156160] via 192.168.12.2, 00:00:08, FastEthernet0/0
D        10.3.0.0/18 [90/156160] via 192.168.12.2, 00:00:08, FastEthernet0/0
D        10.4.0.0/19 [90/156160] via 192.168.12.2, 00:00:08, FastEthernet0/0
D        10.5.0.0/20 [90/156160] via 192.168.12.2, 00:00:08, FastEthernet0/0
D        10.6.0.0/21 [90/156160] via 192.168.12.2, 00:00:08, FastEthernet0/0
C        10.10.10.10/32 is directly connected, Loopback10

I have this configuration below:
router eigrp 1
 distribute-list route-map FILTER_IN in 
ip access-list standard NET_1
 deny   10.0.0.0 0.0.255.255
route-map FILTER_IN permit 10
 match ip address NET_1

Open in new window


Now if I run sh ip route , I will see the 10.x.x.x  gone except for the Directly Connected ..

My question is what if I want to keep just  these 3 routes below in the routing table. how would I change the wild card mask.

D        10.2.0.0/17 [90/156160] via 192.168.12.2, 00:03:04, FastEthernet0/0
D        10.3.0.0/18 [90/156160] via 192.168.12.2, 00:03:04, FastEthernet0/0
D        10.4.0.0/19 [90/156160] via 192.168.12.2, 00:03:04, FastEthernet0/0

Thank you
jskfanAsked:
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Ken BooneNetwork ConsultantCommented:
So lets start with the subnet mask that would match that first:

A 255.254.0.0 subnet mask  would mask 2 numbers starting from 0 which means the first subnet would cover 0 and 1, the second subnet would cover 2 and 3, and the next subnet would cover 4 and 5.

If you change the mask to a 255.252.0.0 the first subnet would include 0 through 3, and the next would cover 4 - 7.

So you couldn't cover those 3 subnets until you went to the next subnet mask which would bet 255.248.0.0 which would cover 0 through 7, but that would give you subnets that will not work.

So from a subnet mask mask perspective you would have to use 2 statements to cover those numbers:

You could use 10.2.0.0 with a subnet mask of 255.254.0.0 which would cover 10.2.0.0 and 10.3.0.0 and then you would have to do a 10.4.0.0 with a subnet mask of 255.255.0.0.

Now that you have that lets do the wildcard mask which is really the inverse of the subnet mask.
255.254.0.0 would have a wildcard mask of 0.1.255.255
255.255.0.0 would have a wildcard mask of 0.0.255.255

I hope that helps.
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jskfanAuthor Commented:
I thought  subnet mask , for instance:


10.3.0.0/18  = 255.255.192.0

wildcard Mask =0.0.64.255

10.4.0.0/19 = 255.255.224.0
Wildcard mask= 0.0.31.255
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Ken BooneNetwork ConsultantCommented:
Oh I’m sorry I missed the /18 /19 etc.  I read them as if they were slash 16 routes
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Don JohnstonInstructorCommented:
deny 10.1.0.0 0.0.255.255
deny 10.5.0.0 0.0.15.255
deny 10.6.0.0 0.0.7.255
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jskfanAuthor Commented:
Thank you Guys..
I will come back to this topic later.
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