Using RFC 1918 IP Addresses on Internal Routers?

braek asks: "Our network has expanded to the point that I have about 6 separate network links to remote networks. I would like to avoid using public IP addresses for the routers to conserve my limited global IP addresses, and I don't expect any additional IP's for a while. :( What do you guys think about assigning internal routers a private, RFC 1918 IP address, like 10.0.0.1 or something? (For security, RFC 1918 addressess would be filtered at the border routers.)"

"I am testing this right now, and routing seems to work fine, the only problem I can think of, is when someone does a traceroute, it will show up like:

10   120 ms   131 ms   120 ms  152.63.67.97
11   130 ms   130 ms   131 ms  66.141.21.1
12     *        *        *     Request timed out.
13   130 ms   130 ms   140 ms  66.141.21.185

Hop 12 is the router with the private RFC 1918 address, and I am assuming it is not responding to a traceroute because the IP is not globally routable. However, all the clients behind the router have complete, unabashed network access. What problems may one encounter if implementing this kind of addressing scheme?"

Comments

Re:Only one issue

[anticypher]

I see at least one 10/8 network:
2 10.55.160.1 11.023 ms

Nope. It looks like a 10.55.160.1/30 point to point link between the uBR headend router for your neighborhood and the core routers in Cincinnati. Since the uBR is only collecting traffic and passing it on to the core, it never needs a routable interface, hence RR is doing a technically valid thing.

There is nothing wrong with using an RFC 1918 address for internal links. Many ISPs use them for point to point links to conserve IP use. So what if RR is using a 10 address on one of their internal links? Your packets are still being routed, your traceroute got to /., and you were able to post wrong information :-)

Its not the wrong thing to conserve IPv4 address. Its good practice, every one should be doing it.

Routers should respond to all valid IP addresses, even RFC1918 addresses. What shouldn't be done is to route those packets to the internet. If your border routers are participating in BGP4, then they should be dropping any packets with source or destination matching RFC1918, and should ignore (filter) any route to an RFC1918 net. There are lots of badly configured border routers out there spewing route advertisements for private network ranges, just learn to filter them out, and make sure you filter your own out.

the AC