BGP Question

Discussion in 'Cisco' started by nospam@nospam.com, Mar 4, 2005.

  1. Guest

    Hi,

    We are looking to setup a small ISP with a number of servers in, but
    we are wanting a number of IP ranges. The servers wil be located in a
    carrier neutral data centre and we will want a few connections to
    ISPs. We will be getting differnt IP ranges from each ISP.

    Redundancy is very important for the application too, and it seems
    like a waste to get multiple connections from many ISPs and not use
    BGP.

    My BGP knowledge is not amazing, but would it be possible to have a
    few small blocks say a /24 from each ISP and announce these blocks
    through BGP, or would this not work as the ISP would annouce the block
    aswell with a longer prefix.

    If we applied for our own PA space then there would not be this
    problem, but we are looking for a range of different IP addresses for
    this application. What would happen if we did announce the /24s would
    they get filtered out further upstream or just get ignored anyway due
    the ISPs announcement?

    Would traffic get routed to our routers regardless? If the link to an
    ISP did go down that provided a block of IPs would these IPs be not
    reachable?

    Could we apply for multiple blocks of PI space or would this be a
    stupid idea?

    Any help would be appreciated and if none of my suggestions above
    would work is there any way of creating a redundant network while
    using multiple connections to ISPs.

    Thankyou
     
    , Mar 4, 2005
    #1
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  2. Iggy Guest

    Hi,

    I had this problem too and I have been told by tech. support of my upstream
    ISPs that the best way is to acquire public C class for us and announce it
    via BGP to several ISPs. Then I suppose, ISP's will announce there own
    ranges + my C class into the Internet. This is because (they told me so)
    Internet BGP routers would filter anything longer then /24 prefix.
    The other way is to get a few subnets of one C class, but then my ISP's
    should be able to summarize those subnets within there address ranges, but
    I'm afraid that it's nearly impossible to get such ideally contiguous public
    IP ranges...
    I have a very little experience with BGP, so I'm just telling you what "big
    guys" told me about it...

    B.R.
    Igor

    <> wrote in message
    news:eek:...
    > Hi,
    >
    > We are looking to setup a small ISP with a number of servers in, but
    > we are wanting a number of IP ranges. The servers wil be located in a
    > carrier neutral data centre and we will want a few connections to
    > ISPs. We will be getting differnt IP ranges from each ISP.
    >
    > Redundancy is very important for the application too, and it seems
    > like a waste to get multiple connections from many ISPs and not use
    > BGP.
    >
    > My BGP knowledge is not amazing, but would it be possible to have a
    > few small blocks say a /24 from each ISP and announce these blocks
    > through BGP, or would this not work as the ISP would annouce the block
    > aswell with a longer prefix.
    >
    > If we applied for our own PA space then there would not be this
    > problem, but we are looking for a range of different IP addresses for
    > this application. What would happen if we did announce the /24s would
    > they get filtered out further upstream or just get ignored anyway due
    > the ISPs announcement?
    >
    > Would traffic get routed to our routers regardless? If the link to an
    > ISP did go down that provided a block of IPs would these IPs be not
    > reachable?
    >
    > Could we apply for multiple blocks of PI space or would this be a
    > stupid idea?
    >
    > Any help would be appreciated and if none of my suggestions above
    > would work is there any way of creating a redundant network while
    > using multiple connections to ISPs.
    >
    > Thankyou
     
    Iggy, Mar 4, 2005
    #2
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  3. Kevin Widner Guest

    the best way is to acquire public C class for us and announce it
    via BGP to several ISPs.

    This would be the best way, however, it is now almost impossible to get
    a /24 assigned from ARIN, not sure about the other regional registries,
    but I would assume that holds true everywhere. I think the smallest
    block you are likely to be awarded these days is a /22 and you must
    show how you intend to use that many addresses. Then you would need to
    get your own AS number allocated for your BGP process.

    If you use an IP block from your ISP, you undoubtedly won't be allowed
    to advertise that block via another provider even if the need arises.
    So, I'm interested in your question as well. I'm wondering how smaller
    companies, (those with needs of only a /23 or less) can effectively
    design a solution for resilient Internet presence.

    I'm afraid the best option for small companies will be to multi-home to
    the same ISP and ask for diverse CO paths from your location. But I'm
    eager to hear what others suggest.
     
    Kevin Widner, Mar 4, 2005
    #3
  4. See comments in line...

    In article <>,
    <> wrote:
    >Hi,
    >
    >We are looking to setup a small ISP with a number of servers in, but
    >we are wanting a number of IP ranges. The servers wil be located in a
    >carrier neutral data centre and we will want a few connections to
    >ISPs. We will be getting differnt IP ranges from each ISP.


    No need, although you'll probably get them anyway. All you need is one
    subnet from one ISP that you can advertise via all of them.

    >Redundancy is very important for the application too, and it seems
    >like a waste to get multiple connections from many ISPs and not use
    >BGP.


    Correct. You need to get an ASN and run BGP with each ISP. This is a
    common requirement and your ISPs should be able to help you out. The
    tricky part is setting up load sharing and optimum routing without
    degrading your availability.

    >My BGP knowledge is not amazing, but would it be possible to have a
    >few small blocks say a /24 from each ISP and announce these blocks
    >through BGP, or would this not work as the ISP would annouce the block
    >aswell with a longer prefix.


    The owner of the shorter prefix must agree to also pass through
    your longer prefix or none of your traffic will come back via the
    link from that ISP. (Longer prefix always wins when BGP routes).

    >If we applied for our own PA space then there would not be this
    >problem, but we are looking for a range of different IP addresses for
    >this application. What would happen if we did announce the /24s would
    >they get filtered out further upstream or just get ignored anyway due
    >the ISPs announcement?


    You don't state where you are, but if you're in North America, you're
    not going to qualify for your own IPv4 space unless you're a lot larger
    than you indicate.

    >Would traffic get routed to our routers regardless? If the link to an
    >ISP did go down that provided a block of IPs would these IPs be not
    >reachable?


    You would still get your traffic. The only time you might run into
    trouble is if the owner of the short prefix stops advertising it
    and all paths to the other end go through ISPs which apply long
    prefix filtering. This is becoming less common as the price of memory
    continues to decline.

    >Could we apply for multiple blocks of PI space or would this be a
    >stupid idea?


    Once you figure out what you really need and how BGP and your
    service providers work (and where they are in the ISP hierarchy),
    the answer to this will be obvious.


    >Any help would be appreciated and if none of my suggestions above
    >would work is there any way of creating a redundant network while
    >using multiple connections to ISPs.


    If this is an important application, spend a little money and
    get help from somebody who does understand BGP. Otherwise, you're
    talking about an expensive learning experience as you discover the
    hard way all the ways not to do a BGP high availability setup.

    >Thankyou


    Good luck and have fun!
    --
    Vincent C Jones, Consultant Expert advice and a helping hand
    Networking Unlimited, Inc. for those who want to manage and
    Tenafly, NJ Phone: 201 568-7810 control their networking destiny
    http://www.networkingunlimited.com
     
    Vincent C Jones, Mar 4, 2005
    #4
  5. Toby Guest

    Sorry for topposting here. My large scale ISP knowlege is small so here is
    my two pence worth.

    As far as I can see larger ISP's will own various Network ranges and can
    allocate subnets to certain customers.

    I will use private addresses for my explanation.

    ISP1 owns 192.168.0.0/16 but allocates you 192.168.1.0/24

    ISP1 will advertise 192.168.0.0/16 to it's Internet peers via BGP, so if a
    packet was destined to 192.168.1.0/24 from a remote area of the Internet
    (Remote AS) it would in the absence of a longer Network match route to this
    ISP1.

    If you had a second ISP, ISP2 that let you advertise via BGP and passed some
    or all of your adverticements to the rest of the Internet via it's BGP then
    you would be able to advertise 192.168.1.0/24 through ISP2 and this being a
    longer network match would influence traffic through ISP2.

    There are several problems here though to overcome.


    ISP2 peers on the Internet might not accept this advertisement as they dont
    want large routing tables.

    ISP1 may not let you and/or ISP2 advertise networks it owns.

    If ISP1 advertises 192.168.0.0/16 only and ISP2 advertises 192.168.1.0/24
    then traffic would only return to you via ISP2 unless it originated from
    other customers in ISP1 and then depending on configuration.

    For optimal routing what you would want is that ISP1 would advertise your
    network range 192.168.1.0/24 as well as 192.168.0.0/16 to it's peers so
    optimal routing would take place from the Internet to yourself. As well as
    your routing to use the BGP adverts from your 2 sevice providers to
    influence traffic from your networks to the Internet.

    Without talking to both ISP's it would be impossible to design what you
    require. Give them a ring that's what they are there for.

    Toby

    <> wrote in message
    news:eek:...
    > Hi,
    >
    > We are looking to setup a small ISP with a number of servers in, but
    > we are wanting a number of IP ranges. The servers wil be located in a
    > carrier neutral data centre and we will want a few connections to
    > ISPs. We will be getting differnt IP ranges from each ISP.
    >
    > Redundancy is very important for the application too, and it seems
    > like a waste to get multiple connections from many ISPs and not use
    > BGP.
    >
    > My BGP knowledge is not amazing, but would it be possible to have a
    > few small blocks say a /24 from each ISP and announce these blocks
    > through BGP, or would this not work as the ISP would annouce the block
    > aswell with a longer prefix.
    >
    > If we applied for our own PA space then there would not be this
    > problem, but we are looking for a range of different IP addresses for
    > this application. What would happen if we did announce the /24s would
    > they get filtered out further upstream or just get ignored anyway due
    > the ISPs announcement?
    >
    > Would traffic get routed to our routers regardless? If the link to an
    > ISP did go down that provided a block of IPs would these IPs be not
    > reachable?
    >
    > Could we apply for multiple blocks of PI space or would this be a
    > stupid idea?
    >
    > Any help would be appreciated and if none of my suggestions above
    > would work is there any way of creating a redundant network while
    > using multiple connections to ISPs.
    >
    > Thankyou
     
    Toby, Mar 4, 2005
    #5
  6. In article <PF4Wd.261$>,
    "Toby" <> wrote:

    > ISP1 may not let you and/or ISP2 advertise networks it owns.


    If ISP1 offers BGP peering, they will most likely allow you to advertise
    their sub-blocks through other ISPs. Otherwise, what's the point of
    providing the BGP service in the first place? Most customers can't get
    their own address space, so it's going to have to come out of one of the
    ISPs' blocks. If all ISPs implemented the policy of not allowing their
    sub-blocks to be advertised, there's no way that most of their customers
    could implement this type of redundancy. They'd be shooting themselves
    in the foot, making their services less useful to a large number of
    high-quality customers.

    I can certainly imagine some small ISPs having policies like this --
    they probably wouldn't provide BGP service at all. But I think you'll
    find little problem with most tier-1 ISPs.

    --
    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
     
    Barry Margolin, Mar 5, 2005
    #6
  7. Toby Guest

    "Barry Margolin" <> wrote in message
    news:...
    > In article <PF4Wd.261$>,
    > "Toby" <> wrote:
    >
    >> ISP1 may not let you and/or ISP2 advertise networks it owns.

    >
    > If ISP1 offers BGP peering, they will most likely allow you to advertise
    > their sub-blocks through other ISPs. Otherwise, what's the point of
    > providing the BGP service in the first place? Most customers can't get
    > their own address space, so it's going to have to come out of one of the
    > ISPs' blocks. If all ISPs implemented the policy of not allowing their
    > sub-blocks to be advertised, there's no way that most of their customers
    > could implement this type of redundancy. They'd be shooting themselves
    > in the foot, making their services less useful to a large number of
    > high-quality customers.
    >
    > I can certainly imagine some small ISPs having policies like this --
    > they probably wouldn't provide BGP service at all. But I think you'll
    > find little problem with most tier-1 ISPs.
    >
    > --

    Although the above is true there may be instances where the customer IP
    range is not accepted by ISP's or it's peers on the grounds that the address
    range is too small. Having multiple small address ranges does impact on
    routing performance as if every customer was able to advertise what they
    liked the Internet routing table would become huge and unworkable. It is for
    this reason I sugested the OP to talk to both ISP's to establish if they
    will be able to advertise the IP ranges they wanted through them before
    signing up and then getting the grief.

    regards

    Toby
     
    Toby, Mar 6, 2005
    #7
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