[c-nsp] [nsp] NxT1 MLPPP

[Bryan Fetzer]

Sort of bringing this back from the dead, but I did some searching on
the web archives and found a similar discussion based on a question that
I have. I have been reading up on MLPPP, and it seems that as Cisco has
improved and/or added features, the documentation has become "spread
out". 

 

The facts in this scenario is as follows, 

1.	We'll have a 7206 Router. NPE-400 based. 
2.	PA-MC-4T1 installed with 3 T1 connections to a single ISP. 
3.	NO Routing protocols going over these links
4.	This is for an Educational institution that will be utilizing
these links to provide streaming video from various places on the net
5.	We have decided after weighing all options to go with MLPPP

 

Questions that I'd appreciate being addressed. Thanks in advance. 

1.	From my understanding, MLPPP is CEF switched now, does this mean
that the commands ip load-sharing per-destination and ip load-sharing
per-packet are able to be used even with a SINGLE MLPPP bundle? (From
David Curran's account below it would be best to run with per packet.)
David, (or anyone else) if you have a chance could you answer if this
was in regard to a single MLPPP bundle or load balancing over more than
one bundle. This may be a moot point if the ISP is currently
load-sharing per destination and are reluctant to change on their end. 
2.	Would link fragmentation and interleaving be appropriate in this
situation? Keeping in mind that we'll want streamed Video/Audio to be
able to get across this link fast. ( this function is documented here:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fqos_c/fqcprt6/qcflfi.htm#wp1003889 ) 
3.	If link fragmentation and interleaving is appropriate, what is a
good setting for the command: ppp multilink fragment-delay milliseconds
setting? 

 

Thanks for the input here, 

Bryan Fetzer

 

David Curran wrote: 

You can bundle 8 links in a group on most platforms.  Some of the very
high-end distributed platforms will allow 12.  It should also be noted
that
IOS will load balance, at most, across 8 paths (used to be 6).
 
Allow me to give some non-scientific anecdotes.  We had a lot Cisco
7206VXR
chassis with NPE400s running MLPPP links.  We ran OSPF and BGP across
them
and some MPLS "stuff" over that.  We ended up having to convert all of
them
to per-packet due to high CPU utilization and just general "weirdness".
The
boxes would run at 40% utilization even at "low tide".  And processor
util.
would increase with load, which is not common with CEF.
 
After kicking this around for a while with Cisco it became apparent that
some of the MPLS features we were running weren't 100% supported and
that
was probably the cause.  There are some features suited for Multilink
interfaces and some that aren't.
 
The moral of the story is, as the previous poster said, don't skimp on
processor, don't expect to be able to run all protocols with any feature
over the bundle, and don't expect a 4xT1 group to actually run like a
factional DS3.  With those caveats in mind, MLPPP is a great technology.
 
If you're trying to decide which to use it may also be useful to
consider
the traffic which will be passing over it.  If its going to be lots of
small
packets, CEF with per-packet will run just as fast as MLPPP.  If its
going
to be lots of large packets mixed in with other traffic you might
benefit
from MLPPPs fragmentation and interleaving.  YMMV
 
Hope that helps,
 
-david