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ping speed

Tue Apr 09, 2013 4:27 pm

I'm used to pinging in my network and getting time<1ms. Lately I have found that one of the 4 reply's will have a larger number in it. If I go to the server and ping back to the original workstation all looks good. I go to a different workstation and get the larger number for one of the reply's. I go to another server and ping the server and get the normal time<1ms. These are all attached to the same 1000mb switch. I reset the switch and have the same effect. I'm just wondering if there is an inexpensive easy way to figure out why this is happening. The switch is not a smart switch.
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Re: ping speed

Tue Apr 09, 2013 5:43 pm

About the only way is to start sniffing with Wireshark on both the server and the workstation and see which packet is late as ping is an ICMP request and reply. I'm assuming it's not the first one that is slower, the first packet may need to ARP request and get an ARP reply if the entry isn't in the ARP cache.
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Re: ping speed

Tue Apr 09, 2013 7:29 pm

One thing to consider is that ICMP messages are considered low priority in the network. If you are pinging the server and sudenly a client makes a request for a chunk of data, the server may not respond to the ICMP ping message until that data is sent. 1ms respresents about 100k of data or so on a 1Gbps link so it wouldn't take much.

Try pinging client to client. If you don't see the spikes, the spikes are coming from the server. Run wireshark on the server and monitor the interface. See what else is going on. While it is possible that it is a switch problem, it is unlikely. If you don't see problems with normal data transfers the switch is probably fine.

How much larger is the "larger number"? Are you having other problems?

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Re: ping speed

Wed Apr 10, 2013 10:43 am

Went to the server. Ping two different workstations, both came back with 4 time<1ms. Went one of the workstations, pinged the server the first was time=11ms, the other 3 time<1ms. Pinged the other workstation, the 1,3,& 4th were time<1ms, but the 2nd was time=27ms. There have been some complaints of a lag time with responses from the sql server app, but also Outlook running pop3 responding (I'm assuming because it is accessing the isp to get email and it's not responding very fast.
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Re: ping speed

Wed Apr 10, 2013 12:13 pm

Windows? You can get a better overall view of your network with:

ping -t SERVER

Hit CTRL-C and at the end you'll get the stats for the pinging.

However, if the complaints are SQL response times, I think it unlikely that a few ms ping spikes are the cause. Maybe a symptom of something else, but not causing SQL to respond slowly. I'd look into CPU, memory, and storage first to make sure one of those aren't the bottleneck.

For Outlook going outside your network to get mail and sometimes being slow about it, yeah, probably has nothing to do with your local gigabit switch.
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Re: ping speed

Fri Apr 12, 2013 8:05 am

Just to be a nit-picker, you don't measure "speed" when you do a ping, you measure the latency.
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Re: ping speed

Fri Apr 12, 2013 2:52 pm

While consistently high ping times can be bad you have to look at what you are measuring.

A ping measurement is a time for a packet to go to another server, be acknowledged and then return to you.

It is not a speed, it is travel time and it is an indication of latency.
Think of a ping as you going to your friends house in your car and back again. latencies would include stop lights and other delays. your friend could take time in answering the door 'cause he is busy on the phone or he could be waiting right behind the door for you to ring.

most of these factors have nothing to do with speed but would impact a neighbours observation of how long you took and may consider you slower.

in the case of the spikes you've seen it is the analogy of the friend being busy on the phone... you just had to wait at the door a little longer :-)

in your example of your measurement there is nothing to worry about, the server you are pinging is just getting a little busier.

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