Odd issue with Ping and switches

[burleyman]

I was helping to troubleshoot a network and I came across something I had not seen before and I am not sure what is causing it.

When I am sitting at my laptop and I do a continuous ping to a switch a few hops away I keep getting timeouts. Now the odd part, if I ssh into a switch and ping from the switch to the switch I am running the ping to and watch my laptop, as soon as I hit enter on the switch to do the ping the pings from my laptop start working at the same time with no drops or crazy delays.

Ideas?

Also if I stop all the pings and go back after some time the same thing will happen.

[Francesco Molino]

Hi

Is the issue solved now?
The switch you were connected to to do ping, was it the switch where your laptop is connected to ?
Before initiation the ping, what looks like the show ip arp on the switch for the remote switch IP? And how it looks like when doing the ping from the switch?
Are you sure there is no duplicate IP?

When you say the ping is not responding from your laptop, have you ensured that remote switch receives icmp packet and not able to answer back or the remote switch never receives icmp packet (doable with debug ip icmp or wireshark on remote switch)
I will wait for your answer before continuing asking for some tests and/or output.

[burleyman]

No it is not solved. I do not have access to the switches at this time to get the ARP information.

I was not able to do any captures due to time constraints.

No duplicate IP address was checked.

The laptop was connected to a switch that was directly connected to the core switch and I was trying to ping another switch that was also directly connected to the core switch. The ping from the laptop was timing out until I ssh into the switch and ping the switch and as soon as I do that the ping starts working from my laptop. I looked at the configs and nothing jumped out to me. My thought is the pings do work when I ping switch to switch so I don't think anything is blocked.

Ideas?

Mike

[Francesco Molino]

Hi,
To move forward, it will be interesting to see what the arp table look like when your ping timeout from the laptop and then works well when pinging from another switch.
there is no correlation to ping the switch from another switch before the ping work from your laptop.
It seems to be an issue with arp/mac address, maybe I'm wrong but after getting outputs, we can confirm or not this theory.

[burleyman]

I know there is not supposed to be a correlation between pinging from my laptop to a switch and from switch to switch but that is exactly what is happening and not to just one switch. It does it with other as well.

I start a continuous ping from my laptop to a switch and it returns timeouts, I let it run for about 1 minute then I ssh into a switch and ping the switch I am trying to reach and as soon as I do that the pings from my laptop are successful.

Now I was using the ping as an example. When I try and ssh to the switch I was trying to ping it fails as well until I ping the switch from a switch and then I can ssh into the switch with no issue.

I wish I could get the ARP information but I will not be able to get that until next week.

Mike

[Francesco Molino]

Ok let's wait next week.