If you're treating them as two separate links (e.g. two POPs, etc.) then
that's correct, it'll be done by the routers choice of load-balancing (L3).
If you are going to the same POP (or box potentially) you can do MLPPP and
have a more effective L2 load balancing.
Otherwise, it's possible to get an iMux DSU (Digital Link is a vendor as I
recall, but there may be others) that allow that magical bonding to occur
prior to the router seeing the link. At that point, the router just sees a
bigger line coming in (some do 6xT-1 and have a 10meg ethernet output to
If you're seeing the balancing the way that you are, most likely that vendor
(I have no specific knowledge about the A-vendor) is doing usage-based
aggregation which isn't exactly a balancing act. The ones at some of my
sites are MLPPP which is a vendor-agnostic approach for the most part.
From: owner-nanog () merit edu [mailto:owner-nanog () merit edu] On Behalf Of
Sent: Tuesday, January 24, 2006 7:28 PM
To: Matt Bazan
Cc: nanog () merit edu
Subject: Re: T1 bonding
Matt Bazan wrote:
Can someone shed some technical light on the details of how two T1's
are bonded (typically). We've got two sets of T's at two different
location with vendor 'X' (name starts w/ an 'A') and it appears that
we're really only getting about 1 full T's worth of bandwidth and
maybe 20% of the second.
Seems like they're bonded perhaps using destination IP? It's a vendor
managed solution and I need to get some answers faster than they're
coming in. Thanks.
More than likely they are not bonded t1's they are just load balanced by the
router which by default on Cisco is per session. Meaning pc1 to t1#1, pc2to
t1#2, pc3 to t1#1. If they are truly bonded with some sort of MUX for a 3
meg port then you would not see the results you are seeing.
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