Re: Multihoming an end user - Debian

This is a discussion on Re: Multihoming an end user - Debian ; At 09:15 PM 9/23/05 -0500, Eric Cunnningham wrote: >My understanding was that if the addresses weren't specifically >allocated to us straight from ARIN, we couldn't truly multihome. I don't think it matters who actually gave u the address block. Once ...

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Thread: Re: Multihoming an end user

  1. Re: Multihoming an end user

    At 09:15 PM 9/23/05 -0500, Eric Cunnningham wrote:
    >My understanding was that if the addresses weren't specifically
    >allocated to us straight from ARIN, we couldn't truly multihome.


    I don't think it matters who actually gave u the address block. Once u have
    an autonomous system number that block should be independently routable from
    anywhere on the internet. Both of ur ISP's will have to agree to accept ur
    routes. Then it's ur responsibility to get ur router to propagate ur routes
    out to them.

    >Otherwise our second ISP would try to route to our first ISP's addresses
    >through that first ISP rather then direct through their link to us. If
    >we apply for an ASN, can we associate our first ISP's /29 (or /24 if
    >need be) to our ASN? Does our primary ISP need to release it to us or
    >be multihomed themselves?


    It depends. U can get ur own brand new /24 block or take over ISP #1's /24
    block. ISP1's router will then have 2 routes to u. First direct, second
    back out through the internet to ISP2. The same goes for ISP2. This is
    rather inefficient since traffic has to backtrack a lot if one link goes
    down. It all depends on how far out ur route can be propagated. Getting it
    all the way to both ISP's border routers is a good minimum. Getting it to
    both of ur ISP's peer's core routers is best. That way traffic can be
    routed appropriately much closer to the source. Path determination closer
    to the source equals better efficiency. U can weight the routes to prefer
    one or the other but I would make them equal. There's no reason to leave
    one link idle. I'm not an expert on eigrp so I can't give too much more
    detail. Multihoming is about the only way to have transparent redundancy.






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  2. Re: Multihoming an end user

    Chris Wagner wrote:

    >At 09:15 PM 9/23/05 -0500, Eric Cunnningham wrote:
    >
    >
    >>My understanding was that if the addresses weren't specifically
    >>allocated to us straight from ARIN, we couldn't truly multihome.
    >>
    >>

    >
    >I don't think it matters who actually gave u the address block. Once u have
    >an autonomous system number that block should be independently routable from
    >anywhere on the internet. Both of ur ISP's will have to agree to accept ur
    >routes. Then it's ur responsibility to get ur router to propagate ur routes
    >out to them.
    >
    >
    >

    I think for me the push for having our own ARIN assigned address block
    comes from avoiding dependence on the ISP that assigned them to you. If
    we get a /24 from our primary ISP, and that ISP goes under or we switch
    providers, we would need to re-IP our network as that block is only
    sub-delegated to us via the ISP's delegation. For our case, this would
    be trivial as we have relatively few devices but I didn't realize you
    can get an ASN without your own IP block.


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