Not able to broadcast using loopback address in hpux.

[joseph kanagaraj]

Hi ,

In hpux , not able to broadcast using loopback address. I wrote sample UDP
client-server program, found different observation on Linux and hp-ux.
In Case of Linux
------------------------
Two server are listening on 127.255.255.255:2206(port) with SO_REUSEADDR
flag set and client application broadcasting the message on
127.255.255.255:2206. Both server application are able to get the client
message.

In case of hp-ux
-------------------------
Two server are listening on 127.255.255.255:2206(port) with SO_REUSEPORT
flag set and client application broadcasting the message on
127.255.255.255:2206. Only one server application is able to get the client
message. Also we observed that sometimes binding with 127.255.255.255:2206
fails with EADDRNOTAVAIL.

Why this different behavior in hpux ? Any limitation on loopback address on
hpux ? Any loopback broadcast address is there in hpux? Any suggestion /
inputs would be appreciated !

Thanks & Regards,
Joseph.

[Steven E. Protter]

Shalom Joseph,

Using broadcast wastes band width and is blocked by any network admins, check this and see if the HP box is sitting in a switch configured to block it.

See that network configuration is consistent in /etc/rc.config.d/netconf

Check the ndd setting on the system (see the man page on ndd) and /etc/rc.config.d/nddconf for anything that is out of the ordinary.

SEP

[Jerome Forissier]

Hello Joseph,

I can't comment on the behavior of HP-UX vs. Linux in this case. However let me suggest a workaround (not tested): you may try using a multicast address bound to the loopback interface.

Indeed, ifconfig shows that the lo0 interface has the MULTICAST flag so this should work. You would use a multicast address like 239.255.0.1 (in the IPv4 local scope range). And you would configure your socket so that it gets bound to the lo0 interface thanks to the IP_MULTICAST_IF socket option. See http://docs.hp.com/en/B2355-90136/ch05s05.html for details.

HTH.

[joseph kanagaraj]

Thanks lot jerome for the information about multicast . I will try with multicast instead of broadcast .

Thanks & Regards,
Joseph.