[c-nsp] GRE throughput on 3750G

[Ramcharan, Vijay A]

Thanks for the clarifications and feedback received from all. 
GRE on 3750 = software switched with no candy and tastes bad :-( 
GRE on 3845 = software switched but with candy so it's more palatable
:-) 
 
Vijay Ramcharan 
  
-----Original Message-----
From: Adrian Chadd [mailto:adrian at creative.net.au] 
Sent: March 23, 2009 12:33
To: Ramcharan, Vijay A
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] GRE throughput on 3750G

On Mon, Mar 23, 2009, Ramcharan, Vijay A wrote:
> All, 
> I'm just looking for confirmation that GRE on the 3750G is done in
> software with the resulting low throughput (~20Mbps with iperf across
> GRE tunnel on 3750G). All testing and reading that I've done indicates
> that the hardware on the 3750 is not especially built for
> "router-specific" features like GRE. A "show int stats" shows that all
> packets on the tunnel interface in a pair of 3750G switches is process
> switched. The same command on a 3845 shows the majority of the traffic
> is hardware switched/forwarded. 

Uhm, unless the 3845 has some sugar I completely missed, its also
software forwarding it - its just that the 3845 IOS is 'optimised' for
software forwarding. The 3845 probably has much higher bus bandwidth
between the CPU and network interfaces. The 3750(G) also probably
has a much slower CPU.

> Just a sanity check before I open a TAC case. 

I bet the answer will be "Don't do GRE on 3750G, its unsupported."

HTH,


Adrian


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