What does it *really* take to multihome with BGP?

[alec.waters]

Hi all,

If one has two distinct connections to two ISPs, the next step might be to propose to them that they run BGP with oneself, and have the two of them advertise my (single) address block to the world.

In the UK (RIPE jurisdiction), what does it really take to accomplish this? Are ISPs willing to peer with mere-mortal customers?

According to RIPE, I need to be physically multi-homed before I can get an AS number, and also be able to present a routing policy to RIPE. This latter requirement implies that I have to have my address block before I apply for an AS number. Where would this block come from? How big does it need to be to avoid being filtered upstream? Would this only really work if I become an LIR?

thanks for any pointers,

alec

[vcjones]

Your ISPs should be able to walk you through the requirements. You need to get them involved anyway, so why not use them. Anyway, to answer your questions:

You get your address block from one of your ISPs.

To avoid upstream filtering, it MUST be at least a /24. Some IP ranges are filtered more heavily, so again, check with your ISPs and make sure they give you a range which meets your needs. Note that if your ISPs are well connected, being filtered will not prevent your address from working as long as the filtering is upstream of their interconnectivity and one of them is advertising a range which includes yours.

And finally, no, you do not need or want to be a Local Internet Registry (LIR) unless you are an Internet Service Provider (ISP).

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

[alec.waters]

Hi Vincent,

Thanks for the reply!

I approached our current ISP about this, who said they'd be up for it. I then asked them about IP addresses:

Alec said:

"So, if MyCurrentISP gave me a /23 out of one of their larger allocations (a /19, say), you'd advertise the /19 and the /23 to your peers? (OtherISP would of course advertise the /23 to theirs)."

MyCurrentISP replied:

"No I'm afraid we wouldn't do this. In order for you to run BGP with us you'd need your own PA address space and AS number.

I'd be very surprised if any provider out there (with any experience) will let you announce part of their PA space through someone else any more. It's a nightmare ever getting the address space back!"

Looks like I'd have to get an address allocation from RIPE rather than one of the ISPs?

alec

[vcjones]

My experience has been just the opposite, so unless things are very different in across the pond (or there has been a major shift in the past few months) I fear it is your ISP which is out of touch with reality. This could make life substantially more difficult for you in your quest for multihoming. Of course, the other option is to get the other ISP to provide your address space out of their allocation or get an ISP which understands today's requirements of IPv4 address allocations.

Here in North America, ARIN policy is quite explicit:

"In general, the minimum block of IP address space assigned by ARIN to end-users is a /20. If assignments smaller than /20 are needed, end-users should contact their upstream provider. For multi-homed end-users, the minimum block of IP address space assigned is a /22. If assignments smaller than a /22 are needed, multi-homed end-users should contact their upstream providers. When prefixes are assigned which are longer than /20, they will be from a block reserved for that purpose. [Policy 2002-3]"

ARIN reinforces their "we don't want to allocate IPv4 addresses to end users" policy with prices starting at US$2500 for a /24.

RIPE's policy is even more restrictive:

"An organisation within our service region may acquire addresses from an Internet Service Provider or directly from the RIPE NCC. However, organisations which require IP addresses directly from the RIPE NCC need to become a LIR. It is recommended that only organisations which require large blocks of addresses (2048 or more IPv4 addresses) apply for membership, although any organisation can apply."

If I'm out of date, hopefully someone else will chime in with their experience.

Good luck, sounds like you are going to need it...

Vincent C Jones

www.networkingunlimited.com