networking problem

[kokcs]

I have a vme cage. Inside the cage
there are one hp 744 card(with graphics
support), two hp 744 card(no graphics
support).Each got a hard disk attached
to each card. There is an interphase
6224 card with two daughter card
attached. This interphase card can
support two different network of
100Mpbs. Perform ifconfig lan0, it
show that lan0 is up. Next perform
ifconfig ife2,ifconfig ife3 to check
the two port on interphase card is up
and running. Open two hp-ux window to
ping 132.10.255.255 and ping
132.13.255.255 concurrently. It return
successful reply from node that respond
to the broacast ping, however after
some time, I received "buffer space not
available, network unreacheable,
return -1 " msg.The network will fail
to continue the braodcast ping. Why is
that so ? Pse reply. Thanks.