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Old 05-08-2012, 05:42 AM   #1
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UDP packet drop during ARP resolution


We are facing an issue randomly and it seems that ARP is causing the issue.

Issue Description
Two applications on LInux on two nodes are communicating, with one sending SNMP Trap packets (UDP packets) after every 2 minutes. Sometimes it is seen that first packet is not sent by the node, and when packet capture is analyzed it is seen that ARP request is sent in the context of the first UDP packet.

Could it be that ARP resolution is the issue of UDP packet being dropped.

Please let me know if more information is required from our end.

Linux Version - 2.6.21
Old 05-08-2012, 02:15 PM   #2
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Yes, the UDP sending could be drop if ARP resolution is failure. You can add a static ARP entry to verify it.
Old 05-08-2012, 02:40 PM   #3
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UDP is connectionless so it can drop packets and that is that.

Some switches might be set to block udp if traffic gets over some setpoint.

Switches could drop based on other traffic.

Bad connectors someplace.

Poor network design or installation.

Any number of other network issues internal or external. Cellphones to radar to motor start up and the list goes on.

Monitor lan traffic to determine causes.
Old 05-08-2012, 10:48 PM   #4
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@nini09 - Thanks for the reply.
The ARP resolution was successful, but could it be that delay in ARP resolution caused the packet drop on the initiator itself?
Old 05-09-2012, 02:25 PM   #5
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Yes, if ARP response take too long time, current UDP packet will be droped because waiting has a timer.


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