BGP - CIDR /24

Discussion in 'Cisco' started by RS, Mar 25, 2005.

  1. RS

    RS Guest

    We are thinking about using our public addresses - a class C (our own,
    first octet 198, not a part of our ISP's addresses). New to this, but
    after some reading, I have some concerns. We will advertise /24 - which
    our ISP will forward. I read that many BGP peers *filter* out the /24's
    to reduce routing overhead. This may introduce latency as peer defaults
    will be used until the route is found. True?
     
    RS, Mar 25, 2005
    #1
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  2. RS

    Ivan Ostreš Guest

    In article <>,
    says...
    > We are thinking about using our public addresses - a class C (our own,
    > first octet 198, not a part of our ISP's addresses). New to this, but
    > after some reading, I have some concerns. We will advertise /24 - which
    > our ISP will forward. I read that many BGP peers *filter* out the /24's
    > to reduce routing overhead. This may introduce latency as peer defaults
    > will be used until the route is found. True?
    >


    If your address space is not a part of your ISP's address space, then
    you could get a limited connectivity in the Internet since there is no
    "less specific" route to your AS trough your ISP.

    The OP would be right if your block was just a part of your ISP's larger
    block, but then it wouldn't introduce latency at all since there's no
    difference to router if route is more or less specific. Routing the
    packet lasts just the same...

    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
     
    Ivan Ostreš, Mar 25, 2005
    #2
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  3. In article <>,
    "RS" <> wrote:

    > We are thinking about using our public addresses - a class C (our own,
    > first octet 198, not a part of our ISP's addresses). New to this, but
    > after some reading, I have some concerns. We will advertise /24 - which
    > our ISP will forward. I read that many BGP peers *filter* out the /24's
    > to reduce routing overhead. This may introduce latency as peer defaults
    > will be used until the route is found. True?


    I think most of the ISPs that do this kind of filtering make a special
    exception for the "swamp" ranges that contain legacy direct assignments
    to individual companies. They'll generally accept blocks as small as
    /24 in those ranges.

    --
    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
     
    Barry Margolin, Mar 26, 2005
    #3
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