North American Network Operators Group

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Re: T1 bonding

  • From: PC
  • Date: Tue Jan 24 20:19:23 2006

Is it AT&T?

If so, they only use Cisco Express Forwarding on the router, or so
that's at least what I was told by the level 1 techs.  If packet order
reassembly is a an issue and the link is oversubscribed (IE: Heavy
VoIP/gaming use), this method isn't the greatest over others like MLPPP,
or per-flow CEF, but in 99% of circumstances it works great (and has
other advantages).  Can you max out the T-1 with two or three separate
"flows" (IE: simultaneous transfers?)  If so, it is possible that they
are doing per flow and not per-packet load balancing.  It should be per
packet.

Call them up.  Once you get screened and transferred to a Cisco guy,
fire away with your questions -- they know their stuff in my
experience.  Or if is your equipment, log into the router and see if ip
load-sharing per-packet is set (assuming it is CEF), and confirm they
did the same.

Off topic, but in my experience MLPPP usually does a better job of
getting 190% of a T-1's speed with two of them.  CEF usually tops out at
around 160-170% with a single flow, but will max out with as little as
two flows.  I don't know why though, and haven't cared since I've never
really had a dual T-1 all to myself without any other users.  2.5
megabit seems to be the single flow norm on our AT&T Circuits at 3 AM
with no usage., 2.8-2.9 with two or three flows.

As for the technical details, here is some reading material that
explains it quite nicely.
http://www.cisco.com/en/US/products/hw/modules/ps2033/products_white_paper09186a0080091d4b.shtml
http://www.swcp.com/~jgentry/cisco/cisco-load.html
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120limit/120s/120s21/pplb.htm
Test file here for speed tests:
ftp://ftp1.optonline.net/test64




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.

Matt


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.

Matt