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BGP Peer Question

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  • 1.  BGP Peer Question

    Posted 10-08-2012 19:34



    I have a question about bgp peering.


    Currently customer subscribe internet access with ISP and given /28 IPs.


    Now customer request to peer BGP with ISP with the following requirement


    - to peer bgp with ISP using customer AS number but remain the IP address from ISP. 


    Can BGP be configure like this?


    I understand if BGP peer, own AS and own IP block is required by both parties. Please assist me further.



  • 2.  RE: BGP Peer Question

    Posted 10-08-2012 22:28


    I don't think there is a problem with this case.


    Customer can peer with ISP using their own AS number.

    In general, ISP will not advertise a /28 to other AS's. They will adevertise a /24 originating from their AS.


    So, I don't see any issues here.




  • 3.  RE: BGP Peer Question

    Posted 10-09-2012 05:52

    Hi sir,


    the scenario:-



    ISP( static------------(||

    *ISP operational IP static route

    *ISP assign block of /28 to customer for their own use. /28 is own by ISP.


    New Setup:

    ISP(ASN ISP)( BGP-------( CUSTOMER)||

    *ISP and Customer run peering BGP-ok

    *BGP run between ASN ISP and ASN Customer-ok

    *Customer want to remain the IP block /28 (which is own by ISP) and advertised that IP block under ASN Customer-not ok.--- This is the issues. how can customer peer with ISP and at the same time advertised IP block thats belong to that ISP.

    By right customer shall peer using their own ASN and own IP block which already register IRR. I dont know if this can be done via BGP peering, peer using own ASN and advertised IP block thats belong to other ISP.


    I think this is not the right way of doing peering bgp. Comments and input very much appreciate. Thank you sir.








  • 4.  RE: BGP Peer Question

    Posted 10-09-2012 08:05

    Hi Chenoi,


    I reckon customer would peer using private ASN. In that case, just configure remove-private on ISP router.

    Even if customer uses public AS, most ISPs will never advertises /28 to its upstream peers. ISPs generate aggregate routes and only annouce them to its peers. I can't see problem here.


  • 5.  RE: BGP Peer Question

    Posted 10-09-2012 16:20


    As mentioned earlier, customer advertisement  ( /28) will not be propgated beyond the ISP AS. As a common rule, ISPs will advertise minimum a /24 to other ISPs , peers, transits etc.

    Therefore the internet will see the /24 or a supernet of the customer's /28 advertised by the ISP. This is perfectly acceptable and most ISPs do this.


    You can talk to the ISP and explain the requirement. They will surely do this for you.



    Moses N

  • 6.  RE: BGP Peer Question

    Posted 10-10-2012 02:11

    Hi sir,


    I have doubts about the ASN and the IP addresses that required to be advertised to ISP. I understand to advertised min /24 or larger block. In this case /28 would not be an option.


    to peering BGP with ISP


    1.Must have own registerd public ASN from IRR

    2.Must have own registerd IP address block from IRR min /24 


    to run bgp i must have own ASN and own public IP block right? I cannot peer with ISP and advertise someone else IP block under my ASN right?


    I'm sorry the question may be simple but I need to understand the possibilities and the option i have.


    Thank you.








  • 7.  RE: BGP Peer Question
    Best Answer

    Posted 10-10-2012 02:22


    You can peer with ISP with your private or public AS number. It doesn't matter.   Whether you have public or private ASN, you can advertise the subnet allocated by your ISP. You are not advertising any other's IP address. It is the IP address space provided by your ISP to you. So, it is not a problem.




    Moses N

  • 8.  RE: BGP Peer Question

    Posted 10-10-2012 03:10

    Thank you to all. 



  • 9.  RE: BGP Peer Question

    Posted 10-11-2012 02:41

    Hi Chenoi,


    You are welcome.


    Just to clarify you further, If you want to have Dual / Multi-homing BGP with different ISPs, then you need your own ASN and own IP block . Otherwise for peering with single ISP, you don't need to have your own ASN and IP block.



    Moses N