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  1. #1
    Join Date
    Aug 2006
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    Minimum CIDR for routing

    Hello,


    I am having a quick question.


    I am going to collocate two servers in a datacenter and I wish to use my own IP addresses (as I’m member of the RIPE).


    My question is easy, as I wish to get a block for this, what is the minimum size of a PI block to make my collocation provider able to route them ?


    Is it /24 PI minimum, or is it also possible to just cut a /28 for this purpose ?

  2. #2
    Join Date
    Feb 2004
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    99% of providers filter anything that's larger than a /24 (or smaller, I always get confused) - but /24 is the most specific prefix they'll accept. As such, you do need a /24 but surely PA from the colo provider would be better for you?

  3. #3
    Join Date
    Apr 2004
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    London
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    Agreed - we filter anything more specific than a /24 on our network.
    Kris - nitrohosting.net
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  4. #4
    Join Date
    Aug 2002
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    Seattle
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    Quote Originally Posted by CrystalVPS View Post
    99% of providers filter anything that's larger than a /24 (or smaller, I always get confused) - but /24 is the most specific prefix they'll accept. As such, you do need a /24 but surely PA from the colo provider would be better for you?
    I believe "longer" is the term you're looking for.

  5. #5
    Join Date
    Oct 2007
    Location
    Deschutes, OR, USA
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    You could announce a /32 if you wanted, the question is would anyone see it? Of course, unless NAT'ed would be pretty much useless anyway! So let's say a /30 is about as low as you could *functionally* go. A /29 would be the minimum for your number of hosts.

    As others have said though, most networks filter at /24 so anything smaller might not be too visible to the rest of the Network. If you have the PI space, you might try announcing the /28 and then check how visible it is. Scale up to a /24 and watch the results.
    --chuck goolsbee, Prineville, Oregon, USA
    Please note: I no longer work for digital.forest in Seattle, WA, as I left them in early 2010 to pursue an amazing opportunity at an amazing datacenter project elsewhere... I do not speak for digital.forest here. However I still know they provide the best colocation in the Pacific Northwest.

  6. #6
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    Thanks all for reply.

  7. #7
    Join Date
    Feb 2004
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    UK
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    It's also worth noting, that free-ix for one have a policy of nothing more specific than /25s can go over their peering lan. I'm sure other IXPs have similar policies. Most of the tier 1s keep their policies similar - just to try and curb GRT growth.

  8. #8
    Join Date
    Oct 2001
    Posts
    1,315
    Just out of curiosity, I read that when Pakistan took over one of Youtube's /24, youtube broadcasted two /25 blocks to take precedence and get their traffic back - if all big isps actually block anything longer than /24, how did that work?

    Thanks,
    Avi Brender
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  9. #9
    Join Date
    Mar 2005
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    Frankfurt
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    it did not work


    see

    ripe.net slash news slash study-youtube-hijacking dot html

  10. #10
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    Western Europe
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    Quote Originally Posted by MaB View Post
    Just out of curiosity, I read that when Pakistan took over one of Youtube's /24, youtube broadcasted two /25 blocks to take precedence and get their traffic back - if all big isps actually block anything longer than /24, how did that work?

    Thanks,
    http://www.ripe.net/news/study-youtube-hijacking.html

    What I've heard so far from a friend working at a NOC for a international ISP...

    Due to the abnormal situtation and being announced on news sites, some reactive ISP accepted those more specifics annoucements to make sure their customers can still access Youtube.

    That was a simple workaround until there was a real fix to the problem.

  11. #11
    Join Date
    Mar 2005
    Location
    Frankfurt
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    isps just dropped the incorrect announcement so that youtube's /24 announcement was active (youtube originally announced a /23, see the ripe document for details)

  12. #12
    Join Date
    Oct 2001
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    1,315
    Thanks for clarifying that :-D
    Avi Brender
    Reliable Web Hosting by Elite Hosts, Inc
    CPANEL Reseller Hosting - Fantastico - Rvskins - ClientExec

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