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

[Hank Nussbacher]

I'd like to revisit CEF load sharing per packet from March 2003:

>] 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.
>
>Likely the providers with whom you've spoken don't want to chew up their
>router CPUs with a per packet load balancing solution.
>
>Just my $.02, of course.
>
>Thanks,
>Rob.

To which Oli wrote:
>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

Does anyone have any concrete RSP and VIP numbers to show what happens when 
switching from per destination to per packet?

Using per destination is not great - take this as an example:
TAU-gp1#sh ip cef s9/1/1
Prefix              Next Hop             Interface
128.139.179.0/24    attached             Serial9/1/1
128.139.220.57/32   128.139.179.2        Serial9/1/1
                     128.139.188.2        GigabitEthernet8/0/0
128.139.251.0/28    128.139.179.2        Serial9/1/1
                     128.139.188.2        GigabitEthernet8/0/0
128.139.251.32/28   128.139.179.2        Serial9/1/1
                     128.139.188.2        GigabitEthernet8/0/0
132.72.0.0/16       128.139.179.2        Serial9/1/1
                     128.139.188.2        GigabitEthernet8/0/0
132.73.0.0/16       128.139.179.2        Serial9/1/1
                     128.139.188.2        GigabitEthernet8/0/0
192.168.4.4/32      128.139.179.2        Serial9/1/1

Was hoping that one /16 would take S9/1/1 and the other /16 would take 
G8/0/0 but:

TAU-gp1#sh ip cef exact-route 0.0.0.0 132.73.0.0
0.0.0.0         -> 132.73.0.0     : GigabitEthernet8/0/0 (next hop 
128.139.188.2)
TAU-gp1#sh ip cef exact-route 0.0.0.0 132.72.0.0
0.0.0.0         -> 132.72.0.0     : GigabitEthernet8/0/0 (next hop 
128.139.188.2)

Becomes more of a hit and miss :-(

-Hank