Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Hypothetical topology:

enter image description here

Cisco supports the diagram on the left as it relates to the Cisco Small Business WRVS4400N Router. As in, both sides of the WRVS4400N are 192.168.1.*, and the routing is handled by the next hop (the NAT router).

The NAT router gives out 192.168.1.* IP addresses (statically or DHCP does not matter to Cisco)

Hypothetically, the NAT router's WAN IP address is with a subnet mask of

But the diagram on the right is not supported by Cisco. I am not getting straight answers about why. Basically, if both sides of the WRVS4400N are 8.105.128.*, and the next hop is the ISP Gateway, all of a sudden this is "a limitation of the device". They can't seem to explain it very well, but they are pointing me to Cisco Enterprise which is (from what I have seen) more difficult to configure and more expensive.

The only technical explanation I can think of that actually might make sense is that 192.* is Class C and 8.* is Class A. The router is said to only support Class C. Something about the difference between Classful and Classless Routing.

Do you think they just want me to purchase a more expensive product or do you think there might really be a difference?

This does not really relate to our purchasing decision. I think we will be using Enterprise just so Cisco will support it. I ask this question because I want to understand what is going on. If there really is something there, I would like to take this opportunity to expand my understanding.

share|improve this question
While I doubt this is related to any difference between glassful / classless routing, I'm also at a bit of a loss to explain Cisco's reasoning for your proposed setup not being supported. Classless routing (more properly Classless Inter-Domain Routing or CIDR) has been around since around 1993, so is very well supported by all current Cisco products. I suspect this is more likely linked to NAT, and whether this router is NAT capable. – Mike Insch Jul 21 '11 at 22:48
What are you trying to accomplish with the WRVS4400N which participated the discussions with With Cisco/Linksys in the first place? – user48838 Jul 22 '11 at 1:16
@user48838 I posted a diagram. I have not actually tried to make it work because it is in use. Even if we got it to work, they would not support it. The PCs will be replaced by either servers or NAT routers (does not matter). The WRVS4400N would have a firewall on it. I personally like it because it is easy to configure and low cost. – George Bailey Jul 22 '11 at 18:24
Based upon your diagram on the right, do you actually have a block of Internet IPs which you intend to assign across the downstream (LAN) side of the WRVS4400N? – user48838 Jul 23 '11 at 3:14
@user48838 Yes. The block is not as big as the example. The PCs are actually servers. But neither of those matter. It is the fact that they are not in a Class C block that seems to matter. – George Bailey Jul 23 '11 at 14:34
up vote 1 down vote accepted

Ok, the issues with Cisco/Linksys is probably not with the IP Class, but actually the IP addressing/routing type/functionality.

The WRVS4400N appears to be not too different than the majority of the SOHO NAT routers on the consumer market. Its specifications do not identify any routing protocols outside of NAT (which is not an actual bonafide routing protocol).

There is a good chance the WRVS4400N will only support NAT address mappings/translations instead of true IP routing. The different between the two is that NAT IP "functionality" will only expose the WAN side to the NAT WAN IP address (e.g. can not directly ping from a WAN device to a LAN device).

There is also a good chance that both diagrams may not be functionally supportable due to the NAT limitations of the device, but the Cisco/Linksys support may have been focused on the IP address assignment and somehow missed the actual functionality limitations.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.