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

[Ian Cox]

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+.

>  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_chapter09186a00803f37a8.html#wp84223
SIP-200
http://www/en/US/products/hw/routers/ps368/module_installation_and_configuration_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.


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!
>~cayers
>
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