4500 switch first icmp packet lost?

Oct 18, 2006 4 Replies

Hello,



when sending a ping to a directly connected station i've the following effect:



switch0#ping x.y.z.2



Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to x.y.z.2, timeout is 2 seconds: .!!!! Success rate is 80 percent (4/5), round-trip min/avg/max = 1/1/4 ms switch0#ping x.y.z.2



Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to x.y.z.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/8 ms



Once there's an entry in the arp table, everything is fine. But why got the first packet lost? Is this a normal behaviour?



Regards, Markus



Hi Markus,

This is normal. The first PING requires the switch to do an ARP for the MAC address, and the first PING times out before the ARP is complete, so the first PING never completes. All subsequent PING's don't need the ARP (the ARP is now cached) so they succeed.

Cheers...............pk.

it depends on the kit.

some stuff will keep the 1st packet in a buffer while waiting for the ARP reply to give a target MAC address for delivery

AFAIR the RFCs allow either behaviour.

This ia normal

CK

stephen wrote:

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