wierd outgoing icmp:type8 for incomming connections

[Ceesjan van Hattum]

Hi,
I've 2 hpux11 systems sending out big icmp-type8
of 1473 bytes for each incomming connection.
It seems to have a memory or caching, because
a second incomming connection from the same
source does not trigger the icmp for some time.

What is the source of this Big icmp?
Regards,
Ceesjan

[Stephen Keane · Accepted solution]

This is a Path MTU Discovery process based on ICMP ECHO Requests. The HP box is trying a large packet size to see if the network/host will allow it. When the client/server have agreed an MTU, it stops sending the requests.

[Ceesjan van Hattum]

Indeed,

In /etc/rc.config.d/nddconf:
TRANSPORT_NAME[1]=ip
NDD_NAME[1]=ip_pmtu_strategy
NDD_VALUE[1]=1

Default, the ndd_vaule is 2.
For online change do:
ndd -get /dev/ip ip_pmtu_strategy
ndd -set /dev/ip ip_pmtu_strategy 1

Regards,
Ceesjan