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I have one P2P Circuit from our HQ to a secondary office. the distance between them is approx 2kms. Earlier when the Circuit was delivered at that time we were having an RTT of 3-4ms. It is a 10Mbps Circuit and when there is traffic flowing on it, irrespective to the amount of Traffic, the Latency reaches to 300-400ms. But when I remove all the traffic from the Circuit then it gives a proper RTT of 2-3ms.

Can you suggest what could be the Issue?

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it.
    – Ron Maupin ♦
    Aug 7, 2017 at 14:58

1 Answer 1

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This is to be expected if your routers are filling the buffers. If you are using ping to test this, understand that ping has the lowest priority.

Depending on your traffic mix, you may want to use QoS to define which traffic gets priority. ICMP should be on the bottom of the list, so ping should still not give you a good number when it is under load.

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  • There is something i would like to add. The gateway for each IP Pool running at the secondary office is configured at the HQ Core Switch. And there are multiple Vlans running at the secondary office. So if there has to be any Inter-vlan communication then the path followed is : Secondary Office -> HQ -> Secondary Office. Now I have Installed a printer at the Secondary Office and it is running on a different Vlan than the other Users. But due to this Latency, the Users are not able to send Print on to the Printer. The Printer gives no Output of the Print Commands given.
    – Sachet.Bansal
    Nov 23, 2015 at 10:27
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    That is less than ideal. It would be better to have a router at each site and use a layer-3 point-to-point link between the routers. You are probably flooding the link with traffic, but ICMP like ping is the lowest priority traffic, so it should show a much slower link when the link is under load, This is to be expected.
    – Ron Maupin ♦
    Nov 23, 2015 at 10:31
  • I tried that, but there is an Issue with that also. The DHCP Server is setup at HQ. It release IP addresses for the host after reading the Vlan Tag of the Request Packet. When I make it a L3 P2P Circuit, the Vlan tag is not present on the Packet. Therefore the DHCP server is not able to find the VLan Tag and not able to release the IP and the users are unable to access the Internet or the Intranet. I cannot install a DHCP server at the secondary office. What should i do now?
    – Sachet.Bansal
    Nov 23, 2015 at 10:36
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    You set up the remote site router with DHCP helper addresses. The DHCP requests will be sent via unicast so replies will be sent as well. We have over 10,000 sites, and almost none have DHCP servers; they use central DHCP servers.
    – Ron Maupin ♦
    Nov 23, 2015 at 10:55
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    That's the real way to handle it. Right now, you have a lot of unnecessary traffic crossing the link. You only want the true site-to-site traffic crossing the link, but you have intra-site traffic for the remote site crossing the link, twice. Ping isn't going to give you the real scoop about your latency, it is really only to demonstrate connectivity.
    – Ron Maupin ♦
    Nov 23, 2015 at 13:37

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