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Can somebody provide me with a use case of using BGP in a large private IP network. (as specified in the BGP wiki.

Two follow up questions:

  1. Also in a broader sense can really BGP be used to advertise a private IP address range?
  2. Can I have my own AS numbers without being registered with IANA in my large private IP network?
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Our network isn't even all that big and we utilize this network design pattern. It just makes manageability easier. Scale-ability just completely goes away as an issue. And ultimately it becomes a little easier to grok what's going on in the network.

The general idea is that the network infrastructure uses OSPF (or IS-IS, or other sorts of IGP routing information), while "customer" routes are carried by BGP. Where "customer" there could be IP blocks at the edge of the network, routes from upstream providers, routes from 3rd party partners and VPNs. The result being that you can look at the source of the route...if its from an IGP, you know that its describing the internal network topology of your network, and if its a BGP route, you know its a "source" or "destination" network (at least from the perspective of your internal network).

We go so far as to have Quagga or other routing protocol implementations on some of our Linux servers...they're peering using eBGP to their upstream routers (typically 2), and inject routes for IP addresses on their loopback interfaces into BGP. Using BGP allows us to put a lot of policy enforcement on the edge routes to only allow the Linux servers to advertise certain specific IPs.

Overall this use case works extremely well, reliable and hugely scale-able. It does take a bit of mind-set change from typical Enterprise network design, but its well worth it, IMO.

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  • Thanks Jeff it is an interesting deployment. I had another question on server fault, let me know your opinions on that serverfault.com/questions/630657/…
    – Subraminion
    Sep 24, 2014 at 0:02
  • Honestly, I don't have a great deal of experience with dealing with non-backbone OSPF areas (when you use the network design pattern above, you have to have a really huge network to have any real need to break up OSPF into separate areas), but I gave something of an answer for it, at least with respect to how OSPF interacts with GRE interfaces/tunnels.
    – Jeff McAdams
    Sep 24, 2014 at 2:42
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  1. Sure, why no. An address is an address.
  2. Just use AS numbers reserved for private use. See RFC6996 for details.
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  • Thanks Jens! But I just need to ensure that either these addresses or private AS numbers do not get propagated to the public network.
    – Subraminion
    Sep 24, 2014 at 0:02
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    Usually any prefixes with those ASN are blocked, like routes to private network (10/8, 172.16/16, etc.)
    – Remi Letourneau
    Sep 25, 2014 at 20:37
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BGP can be used in large data centers along with IGP as transit, there is one use case developed by Yakov and Cisco lifted this use case for Nexus 9000. This eliminates the STP. We can use any AS numbers as long as we don't leak the traffic into the internet. Still it is recommended to use private ASes.

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