We have a public class C network that our company owns, we're moving from T-1 lines to cable, most of my public servers will be moving to a data center, but I still need the public class C network working, can this be done with a home type router in a Comcast connection?

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    Arghhhh! Classes don't exist any more, they're just a history lesson. You have a /24 network, not a class C. – MDMarra Sep 15 '10 at 11:02
  • Class C does still exist, from a strict mathematical POV (IPs whose binary prefix is 110). I agree that most people don't mean it that way, but who knows, maybe he does have a /24 whose binary prefix is 110, making it both a /24 and a class C – jj33 Sep 16 '10 at 15:06
  • @jj33 - partially right, A class C starts 110 and also has a 24 bit subnet mask. The combination of the two is a class C. – MDMarra Sep 17 '10 at 0:18
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    The original spec determined Class by examining the first three bits. Given an octet of bits {b7,b6,b5,b4,b3,b2,b1,b0}. Looking at the first octet of an ip address; if b7 was 0 then Class A, if b7-b6 = 10 then Class B, if b7-b5 = 110 then Class C.(ref. RFC 791) This means that the first octet has strict numerical boundaries. /24 is not a Class C but /24 is. I agree that using the word class in a classless world should be discouraged, but RFC 1519 makes frequent references to Class. – dbasnett Sep 18 '10 at 12:30

Routing an IP network needs to be done through BGP protocol. So either your ISP let you announce BGP routes yourself, or the ISP does it for you. I'm not a comcast expert, but I doubt that that kind of service is part of their "home" package ;)

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    Yes, that's what I thought, and after finally talking to someone in Comcast that understood what I was talking about you're correct they do not do it. Thanks! – Art Sep 16 '10 at 18:56
  • Consider marking the above as an Accepted Answer by clicking the outline of a checkmark next to it. This will enable future people with the same problem to know immediately what the resolution is. – Kevin M Sep 16 '10 at 19:59

Just to clear up some of the stupidity in this thread...

1) Yes you can OWN a /24. It's called a "legacy netblock", in other words, pre-IRR. Google knows. It's owned, because courts have established property rights in legacy netblocks.

2) A /24 can be "internationally routed" - /24s are still accepted into the routing tables of every member of the Internet Default-Free Zone (i.e. Tier 1 ISPs and others who reach all of the Default-Free Zone)

3) Anyone (who speaks BGP to the Internet DFZ) can route your /24, it's just a question of the business relationship you have with a given ISP. And if you speak BGP, you can originate your /24.

The More You Know(tm).


Technically, I don't see that it would be a problem. I suggest talking to your service manager about your needs for routing to your own /24 over whatever infrastructure your new ISP will hook you up to.


There is a way to do this. You have to have a very cooperative ISP (in addition to Comcast) and, at least in my case, a colocated system there. The company (Linkline) added my /24 to their BGP table and pointed it at my colocated system, which knows how to route packets for (part of) that network over a VPN link to my system that sits behind a Verizon FIOS connection. I've been using this setup for over three years now and it works, although I certainly don't recommend it for high-volume or low-latency applications. I use it for incoming email and ssh, primarily, and a couple of other things.


That pretty much is it - no way. You can route whatever you want, but unless the ISP supports it this is like trying to order a mercedes by calling a pizza service - it will get you nowhere.

What you route through YOUR router is totally irrelevant unless the ISP forwards the packets fourther.

Now, let's see:

We have a public class C network that our company owns

No. You dont own anyxthing - noone does. IP ddresses are not owned, they are assigned like a rental car. That said, a C network is NEVER assigned to someone - RIPE's smallest block that one can get assigned is 4096 IP Addresses. You got a C network from your provider for use with them. YOu kill your provider - the C network gets back to the provider, much as you return a car from a rental agency when you end the rental.

  • Actually, you're correct, we do not own the /24 but it is assigned to our company. We have moved before and always have carried the same /24 range with us and when you look it up it's assigned to us so, if we can get someone to route it the range will be out until we do. – Art Sep 16 '10 at 19:20
  • Ah. Seriously. No, you can not. A /24 IS NOT INTERNATIONALLY ROUTABLE. When you "moved" you must have moved within THE SAME ISP. You can not switch providers with a /24. Check the owner of your ISP on the IP Authority WHOIS database for your country. – TomTom Sep 16 '10 at 20:30
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    It sure sounds like Art is in the USA and may have obtained his block from ARIN. If that is so then he can move it anywhere in the USA, with the assistance of his current ISP. – dbasnett Sep 18 '10 at 12:44
  • dbasnett's comment is correct. Directly assigned class C networks are portable, following around even a small number of individuals who had use for networks of that size back around 1990 or so when they were still available. I'm not sure they're actually US-constrained, that's an interesting question. Having one also allows the registrant to obtain a portable IPv6 network in 2015... – Alex North-Keys Aug 15 '15 at 23:11

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