Community discussions

MikroTik App
 
wilburt
Frequent Visitor
Frequent Visitor
Topic Author
Posts: 84
Joined: Tue Aug 24, 2010 3:07 am

First Ping request timed out

Tue Nov 30, 2010 4:30 pm

hi experts,

I have a very strange issue.

I have connected my RB800 to my Cisco877 adsl modem.

When I ping from the Cisco... everything works fast. however, when I ping from the RB800 or any other device connected to the RB800 the first ping always request timed out, then the following pings come back quickly.

it doesn't matter if I do a ping www.google.com or ping the IP address directly, the first ping always times out. I also increased the wait time for the ping to 10 secs and still no luck.


Has anyone come across this before?
 
alfan
just joined
Posts: 1
Joined: Fri Jun 23, 2017 9:36 am

Re: First Ping request timed out

Wed Sep 20, 2017 10:56 am

Hello,
i am facing same issue , when i ping to any device in my local network i receive first ping timeout. please help for this solution.

regards
alfan
 
User avatar
TomjNorthIdaho
Forum Guru
Forum Guru
Posts: 1048
Joined: Mon Oct 04, 2010 11:25 pm
Location: North Idaho
Contact:

Re: First Ping request timed out

Thu Sep 21, 2017 3:11 am

Often - when a ping is made to an IP address which is located on a local Ethernet port (both devices on the same network), the originating ping device might not know the ARP address (MAC address to IP address). This will sometimes make the first ping fail while the arp-table is being learned.

Most devices will timeout the arp table and auto remove arp entries (some devices are as soon as 30 seconds and others can be as high as 5 minutes). During the arp-table timeout, if something in the arp-table talks, then the timeout for that device is reset and the countdown for that ARP (MAC address) starts over again.

If you ping something, it might be considered normal for a 1-st ping to result in time-out (because the arp table is being learned again for that mac address).

If you have a concern, perform a ping, wait 20 seconds after the results, then ping again. The second ping to a local device on the Ethernet (layer 2 network) should still be in memory and not time-out purged yet , and answer right away.

The reason to occasionally auto-clear the arp-table is because it is possible to have network with a subnet mask of 255.0.0.0 (aka /8) where there is a possible 255 * 255 * 255 devices that could be on the network. A full arp table could consume valuable memory and slow down arp lookups. The arp timeout routine will auto remove old arps & while learning new arps and resetting the arp-timeout for individual arps when the talk on the network again.

You might want to google "ARP timeout" for more information.
I hope this info helps.

North Idaho Tom Jones

Who is online

Users browsing this forum: Delid4ve, mkx, sindy and 96 guests