[c-nsp] Load-balancing T1s on a Cisco 7600

[Cory Ayers]

> -----Original Message-----
> From: Ian Cox [mailto:icox at cisco.com]
> Sent: Tuesday, July 26, 2005 2:11 PM
> To: Cory Ayers; cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] Load-balancing T1s on a Cisco 7600
> 
> At 01:47 PM 7/26/2005 -0500, Cory Ayers wrote:
> >We recently upgraded multiple Cisco 7200s serving as aggregation
routers
> >to Cisco 7606s.  We found that ip load-sharing per-packet with CEF
was
> >not an option due to the distributed architecture of a 7600.  We
> >attempted to use MLPoFR and MLPoATM, but neither of these worked, so
we
> >opened a TAC case.  We were told that multilink PPP isn't going to
work
> >on the 7600 and were advised to have our telephone company bundle the
> >circuits for us and hand us a single PVC.
> 
> MLPPP and MLFR is supported on channelized and clear channel T1/E1s.
> MLPPP over ATM and MLPPP over FR is only supported on  single link in
> the bundle for LFI purposes. These features are only supported on
> FlexWAN/Enhanced FlexWAN and SIP-200. They are not supported on the
> OSM-2OC12-ATM-MM+.

I understand binding a single link to a multilink interface for LFI, but
didn't realize this was the only reason to implement MLPoATM.  Is there
any way to bind FRF.8 (Frame-to-ATM) into a single load-balanced
interface?

 
> >  This is not a valid option as
> >it would affect 500 end-sites and mean dealing with nearly 30
different
> >telephone companies.  Our other option appears to be to remove the
Cisco
> >7600s that we recently purchased in favor of a non-distributed
> >architecture.
> >
> >Currently, we have both Frame-to-Frame and Frame-to-ATM terminating
on
> >the 7600.  The Frame-to-Frame circuits terminate on a PA-T3+ housed
in
> >an Enhanced FlexiWAN.  Multiple DS3 and OC-3 ATM circuits terminate
on
> >an LS-1010 and are fed to the 7600 on an OSM-2OC12-ATM-MM+.
> 
> If your doing frame to frame then you can utilize MLFR FRF.16 if it
> is FR at both ends.
> FlexWAN
>
http://www/en/US/products/hw/routers/ps368/products_configuration_guide_
ch
> apter09186a00803f37a8.html#wp84223
> SIP-200
>
http://www/en/US/products/hw/routers/ps368/module_installation_and_confi
gu
> ration_guides_book09186a00802109bf.html
> 
> >Has anyone successfully configured Multilink PPP over Frame or ATM in
> >this scenario?
> 
> Yes on FlexWAN, Enhanced FlexWAN and SIP-200, see the above caveat,
> it is only supported for LFI, not supported bundling links.
> 
> >Is there a work-around for CEF load-sharing per-packet that will
allow a
> >single flow to utilize multiple T1 circuits?
> 
> Is just a single flow, or is the traffic multiple flows between the
> same two IP addresses. If it multiple flows between the same two IP
> addresses then "mls ip cef lod-sharing full" can balance the flows
> based on the L4 information in the TCP/UDP headers.

A single flow between a client and a server.  For example, a customer is
accustomed to seeing 3M bandwidth (250KB/s+) downloading from a site and
now maxes out at 170KB/s.  One T1 maxes out while the other sits
dormant.  The universal CEF algorithm appears lacking, because even with
multiple flows from different machines we still see one or two T1s ramp
to max and the remaining circuits sit below 30% utilization.

I am looking for any solution that will allow proper balancing of T1
circuits.  I did look at MLFR (FRF.16), but we have been moving away
from Frame-to-Frame in favor of FRF.8 to leverage our ATM switches.  As
a result, straight frame is a minority of our circuits.

> 
> Ian
> 
> >Does the Cisco 10000 (ESR) boast similar issues with load-balancing
> >multiple T1 circuits?
> >
> >The Cisco 7200 has been a work horse for us for many years, but lacks
> >the port density, processor, and Gigabit fabric.  We have upgraded to
an
> >NPE-G1 in some scenarios, but this doesn't address high density
circuit
> >aggregation.  What other routers are people using to fill this need?
> >

Thanks for the information and tips!
~cayers
> >
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