[c-nsp] 6500 Sup720 high CPU load - RP LES Fragmentation unsupported

[Sukumar Subburayan]

The new CEF Fast Forwarding feature supports fragementation of IP 
packets in CEF-path.

The 'RP  LES Fragmentation unsupported' is the number 
of packets punted by CEF to the process level as it was not able to 
fragment the packets for whatever reason. I see there are some internally 
found/fixed bugs which are not in 12.2(33)SRA release, and will be 
available in an upcoming release.

Once thing is not clear is, how the router is receiving > 1500 byte 
packets when you say that on the other end there is only one IP interface, 
which has mtu at 1500 bytes.

I would suggest opening a TAC case and investigating this further.

Something things to consider when working with TAC is :

What type of linecard is on the other side on Vlan71?

It is possible that some jumbo  frame internal ASIC  setting on the 
ingress port on vlan 71 is not set correctly, and hence it is allowing 
larger packet sizes.


sukumar

hence it is allowing  On Sat, 2 Dec 2006, Bernhard Schmidt wrote:

> Hi,
>
> we have a Cisco Cat6500 with Sup720a running 12.2(33)SRA. This box is
> experiencing high CPU load in the IP Input process:
>
> csr1-2wr#sh proc cpu sorted
> CPU utilization for five seconds: 54%/27%; one minute: 63%; five
> minutes: 66%
> PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
> 131   100248440  50432579       1987 23.19% 27.28% 28.14%   0 IP Input
>   7     3076072   6211647        495  0.71%  0.63%  0.62%   0 ARP Input
>
> "sh ip cef switching statistics" shows a high number of packets punted
> to RP because of "RP LES Fragmentation unsupported". "sh int stats"
> shows 99% of the packets being in the Processor Switching path come from
> one routed TenGigabitEthernet-Interface. Most traffic coming in there
> should be routed to a SVI. On the other side of the 10GE link is another
> 6500 Sup720a (running 12.2(18)SXD7), which has only two
> Layer3-Interfaces (the 10GE in routed mode and one SVI).
>
> I could not find anything at cisco.com about "Fragmentation
> unsupported". Someone in IRC suggested it might be due to the first 6500
> fragmenting IP packets coming in without the DF bit set. This could be a
> problem, as the 10GE routed interfaces are set to 9216 bytes and the L3
> SVI are set to 1500 bytes.
>
> ------ Vlan20 SVI - Te2/4 routed ------- Te1/1 routed - Vlan71 SVI
>         (1500)       (9216)               (9216)         (1500)
> 	         ^^^ CPU-Load
>
> Te2/4 shows quite a number of giant packets coming in. Problem is, there
> should be none, as the second box only has one IP interface which is MTU
> 1500. Also it does not show any giant packets on any physical interface.
> The Traffic on Te2/4 suggests that the packets are not jumbos (25Mbps in
> 3kpps), but that could be a bad mix as well.
>
> Can someone verify that "RP LES Fragmentation unsupported" are indeed IP
> packets being fragmented because they are sent on a link with a smaller
> MTU?
>
> Thanks,
> Bernhard
>
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