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Original Question

Suppose that Alice operates a website hosting business in Maine. She has a warehouse full of servers to which a /28 range of public ipv4 space is routed (call it the W.X.Y.Z network). Alice wants to move her business all the way across the country to California. In order to provide consistent service to her clients, she cannot change the addresses (but her clients accept their sites being down for a few days as they are moved to CA).

I would imagine that Alice could simply move her machines, and eventually the routing protocols will rediscover that W.X.Y.Z is in California rather than Maine. Here's the problem: evil Bob moves into Alice's warehouse and sets up servers which claim to neighboring machines that they are the W.X.Y.Z network. The result: website users in Maine are sent to Bob's websites (of course, if https were enabled, this would be detected). So it seems that there must be some more official administrative procedures in order to move the physical location of a network. What are these procedures? What entities must Alice contact?

Edit

I realize that I did not make it clear that my question was not meant to be realistic. Of course website owners should rely on DNS rather than their IP address remaining the same. Of course a /28 network won't require an entire warehouse. I am not secretly Alice asking for advice on how to move my business. To clarify what I am trying to ask, consider the following two situations referencing this map instead. (I believe the map is out of date, but the specifics are unimportant.) ISP Map

Situation 1

Comcast is moving the W.X.Y.X/28 network from Vermont to California. Eventually the routing protocols will let COX routers in Kansas know that they need to send packets westward instead of eastward. How long will it typically take for the network to update itself in this manner? If it is a non-trivial amount of time, is there anything Comcast can do to speed along the update?

Situation 2

Comcast is moving the W.X.Y.X/28 network from Vermont to California. Time Warner Cable decides that this is a good opportunity to try to expand their empire into Vermont. (I know TWC would not actually try to do this. I do not have anything against TWC, I am simply using them as an example.) They set up servers in Vermont which advertise to the network that they are part of the W.X.Y.X/28 network. In this case, COX routers in Kansas will have no way of knowing if the legitimate W.X.Y.X/28 networks lies westward or eastward. What does Comcast have to do in order to notify the other ISPs of the geographic change of their W.X.Y.X/28 network. Is all that they could do ask for the FCC to enforce rules?

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  • Physical location does not matter. What matters is what the connected ASes will accept and advertise. If there is an AS advertising the it owns a prefix when it does not, the ASes to which it connects should recognize that and refuse to advertise the prefix. The Internet is cooperative, with no central enforcement authority, other than peer pressure from the other ASes. In the worst case, trying to do something like that can get you completely cut off from connecting to the other ASes that make up the Internet. – Ron Maupin Nov 24 '20 at 17:00
  • Sorry Mr. Maupin, what does AS stand for? – Sean Letendre Nov 25 '20 at 19:44
  • Autonomous System - the entity that is used to advertise routing prefixes via BGP, between ISPs. – Zac67 Nov 25 '20 at 19:47
  • That is an Autonomous System. The Internet uses BGP for routing, and BGP uses ASes. For example, a company can get an AS and provider-independent addressing from its RIR, then it can connect to any provider AS using BGP, and it can take its addressing and AS with it wherever it may move. Also, most large providers can connect to you in any place in the country because they have a location, and they will contract with the incumbent provideer to connect your location to their PoP, so it is actually pretty easy to move and keep everything. – Ron Maupin Nov 25 '20 at 19:48
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    Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer. – Ron Maupin Dec 16 '20 at 23:44
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EDITED based on question edits:

How long will it typically take for the network to update itself in this manner?

Typically, it would be less than a minute.

They [TWC] set up servers in Vermont which advertise to the network that they are part of the W.X.Y.X/28 network.

No, that's not how it works. The W.X.Y.Z subnet was part of the address blocks assigned to Comcast. TWC would never advertise that block, since they don't own it. If they provide service in the same area in Vermont, they would have their own address block A.B.C.D, from which they would assign addresses to customers.

Previous Answer:

If Alice is using a /28 network, it's an almost certainty that she does not own that address space. Instead, it is owned by her ISP, and the ISP probably advertises that block to the Internet as part of its larger IP allocation. So if she changes her ISP when she moves, the new ISP will not advertise that space to the Internet at large. She will need to get a new address block from her new ISP.

If Alice uses a nation-wide ISP, and they agree, the ISP may allow her to move the block to her new location. But that is up to the ISP.

If Alice has a much larger block registered to her (from ARIN, for example), she can move that block wherever she wants, and she will advertise it to her new ISP who in turn will advertise it to the Internet.

Bob can't advertise any address block unless he has an agreement from his ISP. The ISP will not (or should not) allow Bob to advertise any addresses that don't belong to him. If Bob moves into Alice's old building and has the same ISP as Alice did, that ISP may allow Bob to have the same space used by Alice (since Alice isn't using it anymore).

Practically speaking, the ISP will assign Bob a new block and statically route between Bob and them. So Bob doesn't have the opportunity to falsely advertise addresses.

Since IP addresses can change over time (as in this example), most systems on the Internet use DNS and names to identify services on the internet. The DNS servers will provide the correct address regardless of where Alice's servers are located.

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Answer to original question.

She has a warehouse full of servers to which a /28 range of public ipv4 space is routed (call it the W.X.Y.Z network).

The smallest allocation that can be routed on the public internet is a /24, so this /28 must be a sub-allocation from an ISP. To have a business operation that justifies a "warehouse full of servers" and yet be reliant on a tiny block of IP addresses allocated by an ISP was very foolish of her.

I would imagine that Alice could simply move her machines, and eventually the routing protocols will rediscover that W.X.Y.Z is in California rather than Maine.

Your imagination is far from the reality.

Since Alice's block is allocated by her ISP she is at their mercy. If her ISP has a presence in California, they may be able to move the addresses to a link they provide there. They may be reluctant to do this though as it will complicate their internal routing, and it may well result in sub-optimal routing for her traffic.

If she can't get her ISP to help she is going to be stuck with maintaining some level of presence in Maine and renting a link (or setting up a VPN) from Maine to California.

If Alice instead had a provider-independent /24, she could stop advertising it to her provider(s) in Maine and start advertising it to her provider(s) in California. Unless you are a major network yourself, your providers will probably require evidence of IP block ownership before accepting your advertisements for it. If the provider is smaller, they may have to pass that evidence on to their providers.

Between the major networks, maintaining filter lists starts to get rather impractical. So things generally work on trust. This does cause problems sometimes when a network violates said trust and lets in routes that they should not have.

In order to provide consistent service to her clients, she cannot change the addresses (but her clients accept their sites being down for a few days as they are moved to CA).

This seems unlikely. In the real world alice would almost certainly have to set up some kind of private link for the duration of the migration so that the servers could be moved in smaller blocks with internal re-routing on alice's network.

Here's the problem: evil Bob moves into Alice's warehouse and sets up servers which claim to neighboring machines that they are the W.X.Y.Z network.

Alice should terminate any services she has in her old premises before moving out. If Bob moves in and wants connectivity then it's up to him to negotiate that with providers.

Of course if Alice gives up the IPs as part of terminating said services, then the ISP could reallocate them to bob, that is a risk you take when using provider allocated IPs.


Answer to updated question.

Comcast is moving the W.X.Y.X/28 network from Vermont to California. Eventually the routing protocols will let COX routers in Kansas know that they need to send packets westward instead of eastward.

COX won't know about W.X.Y.X/28. The longest prefixes in the Global routing table are /24s, but prefixes advertised by large ISPs are generally shorter than that.

If an ISP wants the flexibility to move small blocks around the country then they will need to deal with that in their own network.

For larger blocks the ISP can advertise them seperately on the Internet and there can be some advantages to doing so.

How long will it typically take for the network to update itself in this manner?

Generally a route in the global routing table will propagate within a few minutes. If the rules in place allow it.

For the most part though, the internet doesn't care much about where a destination actually is, just what networks it can be reached through.

Large providers will typically run a single large network and will advertise all their prefixes to their upstreams and peers from all locations, though they may sometimes put in place multi-exit discriminators or as-path prepends to influence which exit is chosen.

Comcast is moving the W.X.Y.X/28 network from Vermont to California. Time Warner Cable decides that this is a good opportunity to try to expand their empire into Vermont. (I know TWC would not actually try to do this. I do not have anything against TWC, I am simply using them as an example.) They set up servers in Vermont which advertise to the network that they are part of the W.X.Y.X/28 network.

Ignoring the fact that a /28 is too long a prefix to advertise on the Internet. If Charter (formerly TWC) started advertising comcast address space then it is very likely they would end up receiving some of the traffic that was destined for Comcast. Comcast would NOT be happy about this.

The relationships between the big networks work on trust. Mistakes do happen but they are generally rectified quickly.

What would happen if a major provider started systematically hijacking address space I do not know. I would expect lawsuits to start flying pretty quickly as well as a bunch of extra filters to be put in place at various upstreams and peers of the offending provider.

In this case, COX routers in Kansas will have no way of knowing if the legitimate W.X.Y.X/28 networks lies westward or eastward.

The internet does not work in terms of "westward" and "eastward", it is not some huge mesh of local links. There is not some big common backbone. Each provider has their own network or networks which interconnect with each other as the buisinesses see fit.

Providers generally care far more about who you are than where you are. Whatever rules COX apply to advertisements from Comcast, they will likely apply the same rules at all the locations where Cox and Comcast interconnect.

What does Comcast have to do in order to notify the other ISPs of the geographic change of their W.X.Y.X/28 network.

Nothing, the only routers that need to know the exact geographic location of W.X.Y.Z/28 are those in comcast's network.

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Based on your edit with the map, you seem to be confusing home/residential networking, which is off-topic here, with business Internet service.

Almost all of those providers in your map (which, by the way, is outdated, as Cox and TWC merged into Spectrum several years ago) have both residential and business networks with business PoPs (Points of Presence) all over the country that are connected to their own nationwide backbones. A business can use any of them just about anywhere in the country, and a business will contract with one of the providers that will use a local incumbent carrier to connect the business to the provider PoP. This allows a business to move as you have asked, and the business could reasonably expect to keep its provider and addressing, even if it moves across the country.

There are also other large business providers, such as Verizon, Century Link/Level 3, etc., and they all have nationwide backbones with PoPs in every major city, and you can contract with any of them just about anywhere in the country.


A business can also have provider-independent addressing (/24 or shorter prefix) it acquired directly from its RIR (Regional Internet Registry). The business will have its own AS, and it can connect to any provider and use its own AS and provider-independent addressing just about anywhere with any provider.


What does Comcast have to do in order to notify the other ISPs of the geographic change of their W.X.Y.X/28 network. Is all that they could do ask for the FCC to enforce rules?

Comcast, or any provider, connects to any other provider or company, with which it can agree to a contract. The Internet uses BGP to exchange prefixes between the different providers. There is no central enforcement, and the FCC has nothing to do with it. The Internet is cooperative among companies (ISPs are companies, too), and they use BGP to exchange routing information. Companies that flout the rules will find themselves cut off by the other companies.

If Comcast want to change from where it advertises any networks it owns, the other companies do not care. It gets handled automatically and dynamically by BGP. Other companies only care if Comcast is trying to claim ownership of addressing that actually belongs to some other company. Comcast is free to use the addressing it owns in any fashion it wants, although the providers will not accept or advertise prefixes longer than /24 (this helps limit the size of the global Internet routing table). Comcast can advertise a network from one PoP today, then change it and advertise it from a different PoP on the other side of the country tomorrow, and it is completely up to Comcast.

Each of the providers will have at least one AS (Autonomous System). The point of the AS is that it is autonomous, and no other company can dictate what goes on inside the AS. The AS can extend across the county or even the entire world. The Internet is the cooperation between ASes.

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