This is your opportunity to be a Cisco hero (and to earn a tin of incredible cookies, with the first correct answer.) I suspect that the right person can solve this problem in a snap, but the solution has been eluding us for over a month.
We have been assigned a block of 64 static IP addresses (actually, 61) by Verizon, for our Business FIOS network. Let's call our addresses70.x.x.64/26.
We wish to place a Cisco 1841 directly on the FIOS connection, and then have a handful of devices inside (perimeter network), connected by a simple Ethernet switch. Most of the addresses will be handled by an ISA server (firewall/NAT, which protects our LAN and a separate Web Server zone), but a few other devices will be independent (e.g. a videoteleconference unit which doesn't play well inside the firewall, a wireless router for untrusted devices, etc.)
For many reasons, it would be best if we were simply routing our traffic to the inside of the Cisco, so that our 70.x.x.64/26 subnet is on the INSIDE of the 1841.
The problem we have is this: Verizon's gateway is 70.x.x.1. Unlike our other ISPs, they have NOT assigned us a separate 30-bit subnet with an address for our router (in this case, that would be 70.x.x.2). I think Verizon just expected us to NAT everything immediately after their interface, the way that residential customers do with their Actiontec router/firewall units.
So the problem is: What do we use as an address for the outside interface of our router, which will allow it to route traffic to the gateway, OR, how do we otherwise deal with this problem?
To demonstrate: If we assign our router's outside to .66 (they've told us not to use .65) then we need a netmask of 255.255.255.128 so that we can route outbound through the gateway. Unfortunately, that then defines ALL of our public addresses as being on the outside of the router. We've looked at a long list of solutions, and none of them are very good:
OPTION A: Currently, we have declared our outside interface as70.x.x.126/24. We then force all of our inbound traffic to the inside with a long list of entries such as:
ip route 70.x.x.69 255.255.255.255 FastEthernet0/0
This works, but poorly -- I suspect there's a lot of unnecessary ARPing going on.
OPTION B: We could keep the public addresses on the outside, and then NAT them to private addresses between the Cisco and the perimeter network (e.g.70.x.x.69 --> 10.0.0.69) and then NAT them a second time in the ISA server. Yuch.
OPTION C: We could "steal" the address 70.x.x.2/30 for our outside interface,and hope that it never causes a problem (We've tried this, but have had inconsistent results -- it works, and then when we re-boot our router it mysteriously fails.)
OPTION D: We could assign a PRIVATE address to the outside of our router -- say, 10.1.1.1. But then, how would we direct traffic to our gateway? If we provide a default route just by interface
ip route 0.0.0.0 0.0.0.0 FastEthernet0/1)
then it's got to ARP for every single outbound address. QUESTION: would the following solve that problem:
ip route 0.0.0.0 0.0.0.0 70.x.x.1
ip route 70.x.x.1 255.255.255.255 FastEthernet0/1
OPTION E: You're the genius. Tell us Option E.
I would very much appreciate it if you could cc me directly on any reply.
Fletcher James President Levit & James, Inc.703-771-1549