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

[Hyunseog Ryu]

If I remember correctly, it is related to buffer management for the
router CPU processing.
Since Ping to Cisco router is processed from CPU,
by default, Cisco router will not process the buffer size larger than
somewhere around 17000 bytes for CPU processing.
So in order to make the ping packet larger than that,
I had to type some special command for the Cisco router to process
the CPU for ping larger than that size.
Unfortunately that specific command was purged from my memory,
because it was more than 2 years. ^.^

Hyun


Joe Shen wrote:
> 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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