From: David (d.ankers@xxxxxxxxxxxxxx)
Date: Mon Sep 04 2000 - 10:10:42 GMT-3
Cisco Routers will always perform switching (load balancing over alternate
paths) per destination (or as you say per stream). Per packet load balancing
is achived by disabling advanced switching i.e. fast switching by issuing no
ip route-cache on the interface. When fast switching is disabled, route
selection is done on a per-packet basis. For line speeds of 56 Kbps and
faster, fast switching is recommended as all packets are process switched.
You mention variance, I persume you are talking about (E)IGRP? variance will
only allow non equal paths to be used for load balancing and the rule above
applies. Variance will split the destinations according to the cost of path
i.e. for every 2 packets sent down the 2 meg line 1 will be sent via the 1
meg line on per packet or 2 session per 1 session on per destination.
However, saying this CEF switching will allow per-packet load balancing ( ip
load-sharing per-packet
) however, you don't mention if this is an option or if you are currently
running CEF. Of course per-packet could easily result in out of order
packets so, if you're running voip for example, forget it.
Regards,
David.
----- Original Message -----
From: damien
To: ccielab@groupstudy.com
Sent: Monday, September 04, 2000 3:09 PM
Subject: Out of sequence packets
Has anybody actually seen problems with out of sequence packets in real life
scenarios. The scenario I am interested in is the typical example where
there are switch paths to the same destination with one link for example 2M
and the other 1M? Does anybody have any proof of concept testing done in a
Lab were they can confirm at what different speed ratios you are sure to
experience problems based on certain types of switching etc? I appreciate
that there are a lot of variables in this equation, e.g. type of switching,
size of traffic streams etc, etc. Any information/ experiences would be
appreciated.
Can Variance overcome this issue ? Without reviewing my notes, I can not
remember whether Variance switches on stream or packet. If it is stream. In
theory, if a Router is performing stream switching, is it fair to say that
there should be no out of sequence issues due to the fact that the entire
stream is following a single path with fixed speeds. If per packet switching
is in use, they there maybe issues with out of sequence packets due to the
packets belonging to the same stream being switched via different speed
links.
I could go on an on........ :~)
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