Subject: [lisp] ALT problem

From: aihua zhang <[email-masked]>
Date: Mon, 11 May 2009 11:19:47 +0800

Hi,

   When using ALT to route Map-Request Message in the internet,this message
may be transfered between different ISP Network. here, comes the
problem if intermediate network doesn't support ALT and if they do,at the
different ISP network edge how they use ALT router connect to each other and
get agreement?

-- 
Best regards!

Sincerely,
aiHua Zhang

State Key Lab. of Networking Technology Research Institute, BeiJing
University of Posts and Telecommunications, 100876, P.R.China
Email ：[email-masked]

---

From: Dino Farinacci <[email-masked]>
Date: Sun, 10 May 2009 20:53:57 -0700

>    When using ALT to route Map-Request Message in the internet,this  
> message may be transfered between different ISP Network. here, comes  
> the problem if intermediate network doesn't support ALT and if they  
> do,at the different ISP network edge how they use ALT router connect  
> to each other and get agreement?

Let's say we have 5 ISPs, name them A-E. Let's say an ALT router is  
configured in ISP A and peers with an ALT router in ISP C which then  
peers with another ALT router in ISP E. What is connecting A to C and  
C to E are GRE tunnels. So all GRE traffic from ALT
router A to ALT router C will be transited by ISP B and all GRE  
traffic from ALT router C to ALT router E will be transited by ISP D.

Therefore, ISP B and D do not have to participate in ALT. Note, that  
the ALT topology is a logical topology and two ALT routers can be  
connected together as long as each side has a routable address. Also  
note, the BGP peering addresses are the address *on the tunnel  
interface* so they don't have to be routable because each end of the  
BGP peering connection believes the other side is directly connected  
(via the GRE tunnel interface).

Dino