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

[Bernhard Schmidt]

Sukumar Subburayan wrote:

Hi,

> 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.

Do you have any BugIDs for that? I've been on site today and the traffic 
is generated by a (supposedly) buggy NetApp-Filer which creates 
NFS-over-TCP packets of 1512 bytes (IP) without df-bit set. I guess the 
box tried pMTUd as a start and got some wrong idea about its own 
overhead (forgot the 12 bytes of Options it sent in the TCP header, doh!)

> 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.

The physical ports (6704-10GE and 6748-GE-TX) are configured to MTU 9216 
as well, but the SVI is configured to 1500 Bytes. I guess the size is 
not checked on incoming packets on SVI.

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

Working with our distributor is always a challenge in this regard, but 
I'll have a look at that.

> Something things to consider when working with TAC is :
> 
> What type of linecard is on the other side on Vlan71?

The traffic I've seen was incoming on WS-X6748-GE-TX. Interestingly 
there are no giants listed on the interface in "sh int", but the giant 
counter on the other router (where ingress is 10GE routed) is 
increasing. Different IOS though.

Thanks,
Bernhard