From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Tue Nov 08 2005 - 20:50:44 GMT-3
Hmmm,
I may be way off (more common than would like to) but:
-I don't know why you say CEF is more CPU intensive.
AFAIK, it's not supposed to be so.
And CEF has a static (given that routing does not change) FIB table
based on RIB, so per packet load balancing is not an option.
There is a "full" option where layer 4 data is taken into account for
the hash that determines the neighbour when many active routes exist in
the FIB, but that's it.
Again, AFAIK per packet load balancing requires process switching.
-interface route-caching has some non obvious (to me) semantics.
It does cache ACL policy (i.e. access-group pass/deny) on the flows,
thus impacting at least per packet CPU usage. I don't know what other
consequences it has. And it can be used with CEF.
Hope this helps.
-Carlos
Holmes @ 08/11/2005 12:55 dixit:
> Hi all -
>
> I'm looking at a load-balancing case, where IP per-packet
> load balancing is being done. (I'm using cef, and ip load-sharing
> per-packet).
>
> Briefly, if we were doing load balancing over 2 T1 links, router
> to router, say a router has 2 serial interfaces, if route-cache were
> enabled, it doesnt always have to do a look up, but would
> have an entry that for any traffic with this source / destination
> pair and send all further traffic over this interface (basically
> per-session or per destination load balancing).
>
> With cef, there no such source/destination pair stored, its a
> little more CPU intensive, but we can get IP packet level
> load-balancing.
>
> Now to my question :
>
> Why is `ip route-cache / no ip route-cache configured at the interface
> level, and not at the global level ? Isnt the decision to send a
> packet out to a certain destination over a certain interface made
> before-hand ie. If you configure no ip route-cache at the interface
> level,
> isnt it too late, the path / interface has already been chosen.
>
>
> Thanks for any replies.
-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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