[c-nsp] Catalyst4006 Vlan interface drop ping packet of 18000 byte

[lee.e.rian at census.gov]

My guess is the switch won't reassemble such large packets.

We don't have any cat4000s so I tried it on a cat6500 & the "couldn't
reassemble" counter incremented every time I tried pinging it with a 20K
packet:
c6k_ios>sh ip traf
IP statistics:
  Rcvd:  3807433057 total, 14895998 local destination
         0 format errors, 0 checksum errors, 1001975 bad hop count
         0 unknown protocol, 0 not a gateway
         0 security failures, 0 bad options, 48760 with options
  Opts:  78 end, 0 nop, 0 basic security, 0 loose source route
         0 timestamp, 0 extended security, 78 record route
         0 stream ID, 0 strict source route, 48682 alert, 0 cipso, 0 ump
         0 other
  Frags: 0 reassembled, 0 timeouts, 10 couldn't reassemble

and after pinging the switch with five 2K packets the counters were
  Frags: 5 reassembled, 0 timeouts, 10 couldn't reassemble


Interestingly enough, a 6500 running CatOS wouldn't answer a 20K ping or
increment an error counter:
c6k_catos> sh netstat ip
ip:
        2058646 total packets received
        0 bad header checksums
        0 with size smaller than minimum
        0 with data size < data length
        0 with header length < data size
        0 with data length < header length
        0 fragments received
        0 fragments dropped (dup or out of space)
        0 fragments dropped after timeout
        0 packets forwarded
        0 packets not forwardable
        0 redirects sent

Regards,
Lee



Joe Shen <sj_hznm at yahoo.com.cn> wrote on 03/02/2005 10:05:43 PM:

> Hi,
>
> We use Catalyst4006 to provide L2 ethernet connection.
> The topology is:
>
>
> Server --- Cat4006(1) --- Cat6509 --- Cat4006(2) ---
> Workstation
>
> Both Server and workstation are Windows system.
> Server's IP is 192.168.0.2, workstation's IP is
> 192.168.0.110, Vlan interface on Catalyst4006(1) has
> IP address 192.168.0.144, Vlan interface on
> Catalyst4006(2) has IP address 192.168.0.244.
>
> When we tried to ping 192.168.0.2 from workstation,
> any packet ( 100 bytes to 30000 bytes) succeed; but,
> when ping Vlan interface address on either
> Catalyst4006 can only succeed with packet whose size
> is less than 17000 bytes. Once packet size is larger
> than 17000 byte, no ICMP_Echo_Response is received.
>
> On the other hand, if we attach a
> notebook(192.168.0.145) to fast ethernet interface on
> cata4006 directly, 'ping' could succeed with packet
> size 20000 bytes.
>
> Why?
>
> thanks in advance.
>
> Joe
>
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