Class C Ip's - Basic Network question - ip portability.

Good Day Experts.

I have what is no doubt a rudimentary networking question that I need to be 100% clear on.

We have several class c ip ranges with our ISP (Let's call them Q). They were assigned to us when we got our first T1 almost 15 years ago. Since them we have added multiple T1 circuits from Q.

We need to move to a fiber circuit that will do away with the multiple T1 circuits. We want keep Q as our isp however we are being told that we will almost certainly not keep our ip assignment.

So my question is why not? I've asked them and haven't been able to comprehend their reasoning so I am hoping you can clear this up for a very lay man.

If we are staying with the same ISP why can't we keep our ip's?
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Jan SpringerConnect With a Mentor Commented:
If one provider allows the announcement or announces another provider's address space without permission, that's considered hijacking.

So, you need the LOA from the provider which has the address space to explicitly define your company name, the subnets you are using and the company name that is allowed to announce that space.

'announce' happens in BGP.  If you are not currently doing BGP, then your provider most certainly announces your subnets via BGP for you.

Providers don't typically have too much of a problem allowing another provider to announce a subset of its space as long as the customer using that space is still with them, as well.
Ernie BeekExpertCommented:
I would thing that theoretically it should be possible as long as you stay with Q. So what reasons do they provide for not being able to do that? Perhaps we can make sense of that.
Jan SpringerCommented:
If you keep your original ISP and are only adding another transit ISP, then you may almost certainly use your existing subnets.

Ask your original provider for an LOA that identifies the company and each subnet that it is authorizing "that other isp" to announce.

It's also helpful if your ISP has SWIP'd those subnets to you so that the whois reflects your being allowed to use them.

Get the LOA to the new provider and tell them that you expect them to allow those subnets in their filter to you.
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QuestionManAAuthor Commented:

Thanks for the help.

2 questions:
1. Are you saying that if I stay with Q then I should certainly be able to keep them?
2. Even if we moved to another ISP, Q could allow us to use them?
Jan SpringerCommented:
If you stay with Q, then I see no reason why they wouldn't allow another provider to either accept the announcement of its prefixes or allow the other provider to announce them for you (with an LOA).

If you leave Q, you stand a very likely chance of not being able to announce that space through another provider.  Especially now that IPv4 is almost exhausted.
QuestionManAAuthor Commented:
We do plan on staying with Q.

Could you elaborate on your statement:
If you stay with Q, then I see no reason why they wouldn't allow another provider to either accept the announcement of its prefixes or allow the other provider to announce them for you (with an LOA).

I just want to me certain that I understand it fully.
QuestionManAAuthor Commented:
Thank you. With your help Q agreed in writing to provide the same ip's. Something they did not want to do this morning.
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