Using RFC 1918 IP Addresses on Internal Routers? 43
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?"
As long as you have just plain connections (Score:2, Informative)
Only one issue (Score:4, Insightful)
When I traceroute from my Road Runner Pro connection (which uses statically-assigned routable IP addresses), I see at least one 10/8 network:
Technically, this is the Wrong Thing [tuxedo.org]. Likewise, your routers should never respond to or generate traffic using RFC 1918 addresses.
Re:Only one issue (Score:3, Insightful)
It's not the wrong thing to do provided, as is the case, my computers never have a need to talk directly to my ISPs intermediate routers and their intermediate routers never have a need to talk directly to my DSL hosts. So it shows up as an actual hop in the traceroute, big deal; you might as well think of it as your packet being tunneled through a cloud of routers running another protocol.
I am still free to use those addresses on my internal network all I want without any problems.
(well sort of, they make http://10.5.1.2/ hit the web interface on their proprietary dsl modem to check status, gather line speed and traffic statistics, etc. but so what; there's 24 million 10/8 addresses)
Re:Only one issue (Score:5, Insightful)
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
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
Re:Only one issue (Score:2, Informative)
For the original poster, you don't need to filter packets with rfc1918 source addresses.
Re:Only one issue (Score:2)
My isp uses 172.16.x 192.168.x and 10.x scattered randomly.
Means my traceroutes take longer than is necessary. Of course, I only traceroute when something's wrong, but it *is* an additional irritation when I'm trying to fix stuff.
Re:Only one issue (Score:2)
We do this... (Score:3, Informative)
You'll just need to use the 'shared network' statement (or equivalent if you are not using ISC's dhcpd) to take care of this.
I've done this (Score:1)
--MonMotha
Re:I've done this (Score:2)
Re:I've done this (Score:1)
Andrew
Re:I've done this (Score:2, Informative)
Re:I've done this (Score:1)
Re:I've done this (Score:2, Informative)
Is your friend, look at the -p option which will make the route persistant accross boots of the system. Doesn't work win Win95 though
so a route -p add should solve your problem nicely
My company does this for the global WAN (Score:2)
It is possible, and it is a very good idea. If you have a web presence, this can also allow you to easily add a security layer from your datacenter (least trusted) to your office space with internal file servers (most trusted).
Can and Must (Score:3, Interesting)
Re:Can and Must (Score:3, Insightful)
Here is one scenario; compromise a Windows machine on 10.0.0.0/8 by sending it an email with an auto-executing file type. Have that executable run a trojan with an IRC daemon. Have that IRC daemon connect back to a channel where you have channelops.
Once you can issue commands to the shell running on that Windows box inside that network, use the compromised machine to scan every other host on the internal network for vulnerabilities. You can even use port forwarding on the compromised machine to directly attack other hosts, in a fashion similar to having a VPN. Or, you can bootstrap Gnu-style utilities such as CygWin or NT rootkits to turn that Windows machine into a fairly powerful Unix emulator. Take your pick.
The attack vectors available for compromising a host on a private subnet are many; once a host is compromised, the attacker can do whatever they'd like inside your network, "private", or not.
Re:Can and Must (Score:5, Informative)
Now, most likely, that 10/8 host gets NAT'd to a public address through a firewall. In this case, the IRC scenario is not only possible, but a real tactic used to get past firewalls. Some, firewalls such as the Cisco PIX make it easy to not care about your outbound traffic, so a client making outbound connections to IRC servers isn't necessary going to even be noticed. This is why you have to implement egress filtering on your firewalls and/or routers to block what your users have access to should they ever get trojaned.
In and out (Score:3)
But I was comparing the private network approach with the firewall approach. Neither would hold up with an internal system comprimised. Indeed, it's hard imagine a security that would.
Re:Can and Must (Score:3)
This is why smart admins only use them as yet another layer in their defense perimiter.
Re:Can and Must (Score:2)
*IP contains a method to define a path through a network called source routing, even using private address space it is possible to tell the routers in between how to get to the destination. This method gets around the fact that private address space is not (should not) be held in global routing tables as you tell the router how to get to the destination and not to look it up. Also realise that the fact that a 3rd party, that is *outside* your control, do not carry a route is a not valid security method. Note that turning off source-routing is simple however most admins don't know about it let alone turn it off.
Karma Envy? (Score:2)
I keep getting flammed for saying that private networks are the solution to all your security woes. Which sort of bothers me, because I never said it. All I am saying is that private networks are more effective than firewalls, and less of a pain for your users.
I once worked at a company with a really extreme security policy. It was against the rules to leave your desk without logging out! (Widely ignored of course.) The company firewall was as restrictive as they get. You could use ports 80 and 23 and that was it. No secure sockets (so no ecommerce or banking from work), no Realaudio, nada.
And of course there was a shortage of IP numbers!
Now I work at a place where everybody's on a private net. No fireway to get in my way, no proxy to configure, and no shortage of IP numbers.
This is asking for trouble (ICMP and stuff) (Score:1, Informative)
I'd advise to choose clever subnetting and NATing of your available space, it will save you and the rest of the net lots of pain, although private space might seem to work smoothly at first. The problems will show up when you least need them, but they will.
Re:This is asking for trouble (ICMP and stuff) (Score:1)
Enforcing a mtu at his border router is a neat idea, but if he or anybody else sets up links with a smaller mtu (like tunnels or ppp links) within the rfc1918 net, he will run into problems again and will have to decrease the mtu for the entire network.
A transfer network only takes very few adresses. Conserving IP space is important, but imho the existing space is better used on proper routing than on
Trace will show RFC1918 if YOUR ISP uses it... (Score:3, Informative)
RFC1918 source/destination packets are dropped at the *edge* routers, not "every" router. By edge I mean AS-Number borders, my experience is that anyone with the technical know-how and need for their own AS-number also usually knows to filter those packets to and from their BGP peers and default providers.
Yes, to and from. For laughs I used to put logging on the border routers, to catch packets to/from RFC1918 addresses, as well as BGP advertizements of RFC1918 address blocks. It was amazing the otherwise reputable ISP's and major companies who forgot to filter those things out! Lets just say that it was one reason for my buying my first AMD chip!
Bob-
Isn't that what those are for? (Score:2, Insightful)
Unnumbered IP? (Score:3, Interesting)
See http://www.cisco.com/warp/public/701/20.html [cisco.com] for some more information.
Hmm.. (Score:5, Informative)
I'm a CCIE and been networking 11 years now, 6 with Cisco and I'd only do this is if I really had too and here's why: management of address space. I'm sure (hope) your management of all your public address space is organised and clear. Furthermore nobody would dream of adding a box to the network with a public address without asking you or another admin who would assign one, which case you would go to your speadsheet (or QIP / another tool), allocate one and record the details. With private address space people tend to just add boxes and subnets and pick an address from random out of the air. This is where time consuming issues come about with overlapping address space. If your network is going to stay small and you have full control over all the addresses then you shouldn't have much of a problem but if the network is going to grow a larger, think about the extra admin you might have to do and also if you were to be hit by a bus would the next guy understand it.
You have some cisco semi-hacks to help you out also such as unnumbered links and also note
RFC1918 has almost universal effective use. (Score:4, Insightful)
I cannot think of a situation, even a single end-point PC, that would not benefit from intellegent and thoughtful use of RFC1918, and even that single PC, if it offers no externally accesses services, has no need for a globally routed IP address of its own.
For all its faults, AOLs use of externally invisible addresses has meant 33 million surfing consumers without wasting routable IP addresses. The masses are (comparitively) secure from DOS and crack attacks, and the technically astute ones can still get little patches that let IP native software on their AOL attached machine work fine.
Even the Mom&Pop dial-up ISP customer, or DSL or Cable subscribers can benefit by only paying for globally routable addresses if/when they want to offer services, or the service provider can simply not offer such routable addresses. The vast majority of home users won't notice the difference.
And anyone with an internal point to point circuit can use RFC1918, anyone who uses a "real" router to link to their ISP (that includes *nix running IPMasquerade) benefits by putting their internal office on RFC1918 address except those few machines that are offering services to the outside world. And if their business depends on it, why are they putting the server in their office anyway? That's what professional datacenters are for.
Of course it can cause problems if done randomly or without consideration that yes indeed this same "10.0.0.1" is used by thousands if not hundreds of thousands of other 'Nets around the world.
However, the benefits of implementing RFC1918 far outweigh the potential problems. At the absolute worst, two sites might have to use masquerade between them to hide the fact that years before they knew they would be working together, they both used 10.0.0.1. That's it, that is the one "danger", and it's little more than another option on the (hopefully used, like a condom) firewall that is also installed between the two offices.
Re-reading, this is in fact a "big picture" spewing on my part. I really wish the "doom and gloom" nay-sayers on both sides, the "We're Running Out Of Addresses" and "RFC1918 Use Is Dangerous" would take cold showers and relax.
Extensive use of RFC1918 is saving lots of money in those places like Asia where routable addresses cost a bundle, and putting off IPv6. Renumbering at some point is the greatest "danger" that any use of RFC1918 can cause, and not using it will require renumbering any time someone changes ISP's anyway. Such is not the case if you're already using unrouted addresses. Something to think about, with the merger/failure cycle in ISP's, ne?
So my advice, do RFC1918 where ever you can!
And for the "I'm Sid, so there" urge, the CCIE "certification" didn't exist yet at the time when I took all the Cisco classes. So There!
Bob-
1918 addressing and when it should be used.. (Score:2, Informative)
Companies will then use the private addresses on there internal networks. This concerves the public addresses for the direct addressing on the internet.
Routers will route anything that they are not speciffically told not to. The general consensis is that you should not route private addresses past your border routers (ie to the outside world). Likewise you can't expect that anyone will be able to get to your machine if it have a private address. ie. 10.1.1.1.
The only people that expressly don't route private addressing are the core internet people. This is done usually done by filtering out these addresses at the edge of each of the large internet providers. Typical firewalls will filter out private addressing as well.
Don't assume just because you are using the private addressing on your network that you are safe. This is simply not true. Generally if you are using private addressing on your internal network there is a router or firewall between you that converts your private address into a registered one(NAT). Someone that is paying attention at this point will figure out that if the core providers filter out the private addresses and if I am on a machine with a private address that I won't be able to go very far on the net(unless there is a address translation inbetween).
There are several ways that NAT's can be assigned one is dynamic (more secure) and one is static. I assure you that if your machine has a statically assigned NAT address and there is no firewall between you and the net that your machine might as well be on the net directly.
Subject: Should isp's use private addressing? Well this is a hard question to answer. If they have a office lan that is behind a firewall that very well could be privatly addressed...
Should they use private addresses on interlink segments. Personally I say no because I really hate it when traceroutes don't return addresses. Although if you want to hide a couple of routers or firewalls in your path it's not a horrible way to do it.
Private networks and security: The only security that private networks provide you is this. If the people that are trying to hack into you are beyond a firewall or provider that filters private networks your are safe until they break into a machine on your network that has registered addresses. Then they have as much access as you network will allow. (note that alot of times this machine may be on your network beyond your defences.
Finally: before you decide to inplement large networks that use private addressing you need to think about who you may be connecting to yourself. On a network each machine must have a unique address for life to be happy. If you have a several thousand host network addressed in the 10.0.0.0 range and your company buys another company that alsi uses the 10.0.0.0 range of addressing life can get very very complicated. I know this from experience.
my two cents... I hope this makes sence.
-Geoff Kuchera
NANOG (Score:4, Interesting)
Its a great list, and has a lot of very knowledgable people on it.
seen this before (Score:1)
RFC1918 on Internet Routers == BAD BAD BAD (Score:2, Informative)
The most important thing it breaks is PMTU discovery, which may cause stalls in your IP transmissions through that router.
... but leave out the zeros??? (Score:1)
Re:... but leave out the zeros??? (Score:1)
Static Nat (Score:2, Informative)
this is how you do it on a cisco on your WAN router. (assuming that you know to configure it):
ip nat inside source static 10.x.x.x 12.34.56.78
now you have a static where internally 10.x.x.x is the ip of the router, but the outside world can see it as 12.34.56.78
a quick google search brought up this -- http://www.cisco.com/warp/public/556/9.html [cisco.com]
ICMP (Score:1)
One major real-world problem: IP range collisions. (Score:2)
When you use a random 10/8 subnet for some of your internal hosts, then your company buys/merges with/is acquired by another company that is using their own overlapping segment of RFC1918, somebody is going to be stuck with a major renumbering project or a really ugly NAT table.
I just got hit by this last fall. We bought a small company (500 employee), and needed to integrate them into the corporate WAN, but their production LAN with hardcoded IPs scattered all over 172.16.X.X, with everything on a flat /16 netmask (single broadcast domain).
Not fun. Ended up with a huge static NAT table condensing their hosts into a single Class-C of real routable space. Ugly and a pain to maintain.