[c-nsp] Re: [j-nsp] load balancing between multiple BGP links

[Oliver Boehmer (oboehmer)]

Alok <> wrote on Wednesday, September 14, 2005 3:08 PM:

> ----- Original Message -----
> From: "Guy Davies" <Guy.Davies at telindus.co.uk>
> To: "Joe Shen" <sj_hznm at yahoo.com.cn>; <juniper-nsp at puck.nether.net>
> Cc: <cisco-nsp at puck.nether.net>
> Sent: Wednesday, September 14, 2005 4:20 PM
> Subject: RE: [j-nsp] load balancing between multiple BGP links
> 
> 
>> Hi Joe,
>> 
>> It can't with the physical layout you described.  BGP selects one
>> next-hop 
> as the best (and only one).  The only way to load share is to have
> two (or more) parallel links between just two routers.  You then
> create a static route on each end via each physical next-hop to the
> loopback on the far end router.  Then, you setup an ebgp multihop
> session between the loopbacks on the two routers.  That then uses IGP
> load sharing to balance traffic across the two parallel links.
>> 
> 
> Anyone knows what to expect in this scenario?
> 
> R1===========R2
> 
> EBGP multihop between them over 2 links
> link 1 =10Mbps
> link 2 = 20 Mbps
> 
> total traffic = 25Mbps
> 
> Is there a way to ensure that link 1 doesnt get choked?

with ebgp multihop, there is no way to prevent one path being choked.
But you might want to investigate "BGP Link Bandwidth" feature ("bgp
dmzlink-bw"/"neighbor x.x.x.x dmzlink-bw") to provide unequal cost
load-sharing in such a case.

	oli