Receving ICMP Packet on VLAN interface

[Bharat Katkar]

Hi Friends,

We have a application which composes ICMP echo request packet and sends over to virtual lan interface. It then expects an ICMP echo reply on that virtual LAN interface.
Somehow i am not receving that reply packet and doubt whether that packet is been discarded by the base interface (Physical Interface) since the MAC received must be of virtual LAN interface.

Can anybody around tell me what exactly is happening and how i can get that ICMP echo reply packet??

Thanks for all your valuable suggestions.

Regards,
Bharat

[RAC_1]

Have you that service (echo) enabled in inetd.conf and have required port open??

grep -i echo /etc/inetd.conf
/etc/inetd.conf:#echo stream tcp nowait root internal
/etc/inetd.conf:#echo dgram udp nowait root internal
/etc/inetd.conf:#echo stream tcp nowait root internal
/etc/inetd.conf:#echo dgram udp nowait root internal
grep -i echo /etc/services
echo 7/tcp # Echo
echo 7/udp #

[Arunvijai_4]

Hi Bharat, Are you loosing the packet in the middle or it is not being generated by your application. In both the cases, analysing with packet capturing tools such as TCPDUMP or Ethereal will definitely help you.

-Arun

[Prasanna H. Kulkarni]

Hi RAC,

This is Prasanna, Bharat's friend.

Below is what we have on our systems:
# cat /etc/services | grep -i echo
echo 7/tcp # Echo
echo 7/udp #

# cat /etc/inetd.conf | grep -i echo
echo stream tcp6 nowait root internal
echo dgram udp6 nowait root internal

--
thanks and regards,
Prasanna

[RAC_1]

Does this setup involves two different cards on two different machines?? If yes, is there a gateway/firewall between?? Is ICMP allowed (at least echo) on it??

Also packet trace would be helpful.

[Bharat Katkar]

Hi RAC,
How are you doin man.
Well you said:
Does this setup involves two different cards on two different machines?? Yes
If yes, is there a gateway/firewall between??
No
Is ICMP allowed (at least echo) on it??
Yes

Basically we have a two VLAN's on a one single interface say vlan1 and vlan2 on system SYS1. Now base NIC card has one MAC address and both vlans's have different MAC addresses. Similarly on the other machine SYS2 we have vlan1 and vlan2.

Now we expect vlan1 to talk to vlan1 and same for vlan2.

But when our application sends ICMP echo request on vlan1 of SYS1 and expect ICMP echo reply on vlan1 it is not happening. This is were we are stucked at.
What we suspect is whether packets supposed to be recevied on vlan1 are discarded by the physical (base) card since it's MAC address is different.

Thanks a lot for your suggestions.

Regards,
Bharat

[RAC_1]

Why you have two different MACs for two vlans?? How you have defined it??

Also did you look at
netstat -p icmp
Monitor it and see it you see anything there.

[Prasanna H. Kulkarni]

Hi RAC,

We did not configure any MAC addresses. The server side VLAN configuration sets up two MAC addresses. I followed SAM steps to configure these virtual lans.

[rick jones · Accepted solution]

FWIW, the "echo" services in inetd.conf have absolutely nothing to do with the handling of ICMP Echo Requests or Replies.

The suggestion to start tcpdump tracing is a good one. Make sure the ICMP echo request arrives at the destination, see if the response arrives at one of the interfaces in the system.

How are you instructing the stack to send/route the ICMP echo request you are generating?

[Jay Kidambi]

First try connecting two HP-UX systems back-to-back (without a switch in between). The interfaces connected this way should both be configured with the same VLAN ID. Then check if ping works. If it does, the problem is most likely on the switch. Check to make sure that the VLAN ID had been configured correctly on the switch port (this should most likely be a "tagged" VLAN).

HTH,
Jay

[Bharat Katkar]

Thanks a Lot friends.
It helped to resolve our problem.