[nsp] ip load-sharing per-packet - cef accelerated ?

[Chris Whyte]

Oliver,
 
What's your definition of "CEF accelerated?" Maybe I (and others?) have mis-understood. I interpreted this term as some advanced mode of CEF switching figuring that most of us already understand that platforms like GSR can only do CEF and, therefore, there was no other choice in this case. So, you're saying that CEF accelerated is equal to regular CEF switching, correct? If so, then your answer make sense to me.
 
Thanks,
 
Chris

________________________________

From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com]
Sent: Mon 3/10/2003 11:13 PM
To: Dan Hollis; Rob Thomas
Cc: Cisco List
Subject: RE: [nsp] ip load-sharing per-packet - cef accelerated ?



All,

just to clear this up (some wrong information has been floating around in this thread):

"ip load-sharing per-packet" is CEF accelerated, there is no significant overhead when it comes to router performance compared to cef per-destination (I'm now only talking about non-GSR systems). The sole difference between the two is how we select one of the 16 loadsharing bucket when we switch a packet.

cef per-destination (the default loadsharing method) uses a hash with <source,dest>, so the name is a bit misleading. It does NOT balance per destination address only, as someone mentioned. And it also does not load-balance per micro-flow as L4 information or protocol# is not used while building the hash.

There is a command "show ip cef exact-route <source> <dest>" which can be used to find which path a given session (<source,dest>) will take:

r1#sh ip cef 2.0.0.0 internal
2.0.0.0/8, version 14, attached, per-destination sharing
0 packets, 0 bytes
  via Serial2/0, 0 dependencies
    traffic share 1
    valid adjacency
  via Serial3/0, 0 dependencies
    traffic share 1
    valid adjacency

  0 packets, 0 bytes switched through the prefix
  tmstats: external 0 packets, 0 bytes
           internal 0 packets, 0 bytes
  Load distribution: 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 (refcount 1)

  Hash  OK  Interface                 Address         Packets
  1     Y   Serial2/0                 point2point           0
  2     Y   Serial3/0                 point2point           0
  3     Y   Serial2/0                 point2point           0
  4     Y   Serial3/0                 point2point           0
  5     Y   Serial2/0                 point2point           0
  6     Y   Serial3/0                 point2point           0
  7     Y   Serial2/0                 point2point           0
  8     Y   Serial3/0                 point2point           0
  9     Y   Serial2/0                 point2point           0
  10    Y   Serial3/0                 point2point           0
  11    Y   Serial2/0                 point2point           0
  12    Y   Serial3/0                 point2point           0
  13    Y   Serial2/0                 point2point           0
  14    Y   Serial3/0                 point2point           0
  15    Y   Serial2/0                 point2point           0
  16    Y   Serial3/0                 point2point           0
r1#
r1#sh ip cef exact-route 1.1.1.1 2.2.2.2
1.1.1.1         -> 2.2.2.2        : Serial3/0 (attached)
r1#sh ip cef exact-route 1.1.1.2 2.2.2.2
1.1.1.2         -> 2.2.2.2        : Serial2/0 (attached)
r1#sh ip cef exact-route 1.1.1.3 2.2.2.2
1.1.1.3         -> 2.2.2.2        : Serial2/0 (attached)
r1#

Please also check http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fswtch_c/swprt1/xcfcefc.htm#1000944

        oli


> -----Original Message-----
> From: Dan Hollis [mailto:goemon at anime.net]
> Sent: Dienstag, 11. März 2003 01:07
> To: Rob Thomas
> Cc: Cisco List
> Subject: Re: [nsp] ip load-sharing per-packet - cef accelerated ?
>
>
> On Mon, 10 Mar 2003, Rob Thomas wrote:
> > ] My understanding is that 'ip load-sharing per-packet' is
> CEF accelerated,
> > ] yes?
> > No.  It is per packet load balancing instead of per flow
> load balancing.
> > This puts quite a bit of additional load on the router, and
> may result
> > in out of order packets arriving at the destination.  I recommend
> > against it.
>
> Are you sure per-packet isn't CEF accelerated?
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/switch_c/xcprt2/xcdcefc.htm

Why would it put additional load on the router? Every packet does a CEF
lookup anyway, yes?

Has anyone on this list actually done an analysis of CPU usage for CEF
per-packet vs CEF per-destination?

-Dan
--
[-] Omae no subete no kichi wa ore no mono da. [-]

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