I've got two routers, A and B. A gets some routes over BGP over a VPN connection, and has a leg on It also can access the whole via its default gateway.

B is on It can access via its default gateway.

There is a router between A and B that I don't control (ie I can't peer with it). I can't use multicast traffic between A and B. I could potentially use a GRE tunnel between A and B to get multicast across, though.

I would like:

  • A to have a route to
  • B to have a route to + the routes A got off the VPN connection

  • How could I set this up?
  • Could I use eBGP, iBGP or OSPF?
  • Can I use OSPF at all when there's that router in the middle and I can't do multicast?
  • If using OSPF was possible, should I use multiple areas? Is it necessary (as I need to do route summarization)?

For the curious, the routers are on Amazon on a VPC each, and the VPCs are joined with a peering connection.

  • 1
    Sorry, don't have time for a long answer at the moment... personally I would create a GRE tunnel and route through it (create OSPF ajacency between A and B over the tunnel). Another possibility would be multihop BGP (that would assume the Router in the middle knows the routes though, which at least for the VPN routes sounds unlikely).
    – Daniel
    Oct 14, 2016 at 22:25
  • 1
    GRE tunnel. That would work. Nov 14, 2016 at 2:39
  • VPC Peering Overview Dec 14, 2016 at 3:47
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    – Ron Maupin
    Dec 25, 2021 at 22:50

2 Answers 2


First, you don't normally configure a default gateway for a router; the router could be a default gateway for end-hosts. You could configure a default route for a router, but that route is, not something like You could configure a static route for

As waza-ari points out, you could use a GRE tunnel to peer the routers with OSPF if it is a broadcast medium, or you could configure the interface for OSPF as a non-broadcast medium, but you would need a static route to reach the interface of the corresponding router. Also, eBGP could be used with multihop, or iBGP could be used, but you need a static route to reach the corresponding interface of the other router.

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Ron Maupin
    Jan 7, 2019 at 17:04

If I understand the question correctly.

Try implementing a Point-to-point protocol and bridge the VPN using a secure socket tunneling protocol.

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