sh ip route question

What does this mean?

 172.18.0.0/16 is variably subnetted, 2 subnets, 2 masks

I have 5 routers, 2 in particular are connected together via ethernet cable.  IP on R1 is 172.18.0.1.  IP on R2 is 172.18.0.2.  They are both using 255.255.0.0 subnet.  

How is this 'variably subnetted', and how are there 2 subnets and 2 masks?  I could see the 'L' interface being seen as subnetted, but not the 'C' interface since it is the default mask of 255.255.0.0.

Here is my full sh ip route:
R     172.15.0.0/16 [120/2] via 172.18.0.1, 00:00:06, FastEthernet0/0
R     172.16.0.0/16 [120/2] via 172.18.0.1, 00:00:06, FastEthernet0/0
R     172.17.0.0/16 [120/2] via 172.18.0.1, 00:00:06, FastEthernet0/0
      172.18.0.0/16 is variably subnetted, 2 subnets, 2 masks
C        172.18.0.0/16 is directly connected, FastEthernet0/0
L        172.18.0.2/32 is directly connected, FastEthernet0/0
B1izzardAsked:
Who is Participating?
 
WissamSenior Network EngineerCommented:
Hello,

Variably subnetted is due to the fact that one of them has the default mask of 255.255.0.0 (the /16)
and the second has 255.255.255.255 (the /32).
0
 
B1izzardAuthor Commented:
So variably subnetted is not the same as VLSM?  Any idea why they would consider a class B 255.255.0.0 subnetted?
0
 
Jimmy Larsson, CISSP, CEHNetwork and Security consultantCommented:
It IS subnettet because you have a small part of it with a /32-mask. If you remove that loopback it will not say that it is variable subnetted anymore.

/Kvistofta
0
 
B1izzardAuthor Commented:
I understand why the /32 would be considered subnetted, just not the /16.  I changed my subnet mask to /17 and now it looks like this:
      172.18.0.0/16 is variably subnetted, 2 subnets, 2 masks
C        172.18.0.0/17 is directly connected, FastEthernet0/1
L        172.18.0.1/32 is directly connected, FastEthernet0/1

Now this makes more sense, as there are now in my opinion 2 subnets, the /17 and /32.  But I guess if Cisco says 255.255.0.0 is a subnet, then it's a subnet.
0
 
WissamSenior Network EngineerCommented:
It simply identifies the /16 subnet, to be subnetted variably to a /17 (255.255.128.0) and to another /32 (255.255.255.255) networks.
0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.