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Latency on Cisco routers

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  • Latency on Cisco routers


    I've got a couple of 1803's and an 877 connected with VPN Mesh. 2003 domain, no email SRV, sophos. all hardware less than 2 years old.

    Main site SHDSL 2/2, satelite SHDSL 1/1, 877 @ datacentre.

    The router at the main site (1803) was getting smashed (600- dropout)last week by a rogue TS user after a SQL application installation on server at main site.

    The avg latency is now between 400 - 450ms at main site and below 100ms at sattelite.

    TS users are still complaining it's slow since upgrade.

    I know 450ms is busy but surely this is normal for this 2/2 link running 9 TS users from satellite, AD, 15 users at main site, internet, file and print?

    Any suggestions, comments appreciated. I've had one Network tech say install QOS and another say this may not be the best idea.
    Can anyone give me some ideas?


  • #2
    Re: Latency on Cisco routers

    450 ms is not just busy it's horrendous. I think you need to look at the utilization of the links and see how saturated they are.

    What do you mean 2/2 link? What is a 2/2 link? Do you mean it's a 2 pair SHDSL?

    What are the specs of the DSL lines in terms of speed (1.5mbps, 3mbps,etc.)? If it's a 2 pair SHDSL then I'm assuming it's 4.6mbps?

    As you are using VPN tunnels here the traffic has to be encrypted and decrypted on both ends which is going to add a performance load that will manifest itself as latency.

    When you say the latency at the main site is 400 - 500ms and at the satellite it's 100ms, what do you mean? What is the latency between the sites?


    • #3
      Re: Latency on Cisco routers

      sorry 2/2 = 2Mb/2Mb link.
      I understand the encrypt decrypt overhead of VPN, I'm aux fait with network up to CCNA but that's it. I also get a 1/1Mb link is tenuous.

      The network guy I had out ran wireshark, checked routers and he reckons something internal is smashing the link, he rang me stumped after a couple of hours then rang me back and said he disconnected all TS users at sattelite office and link returned to normal but it hasn't fixed it.

      He suggested turning all TS users off one by one, but they are all off at the moment (no one using the network) and when I ping the router from home I get this
      Packets: Sent = 22, Received = 22, Lost = 0 (0% loss),
      Approximate round trip times in milli-seconds:
      Minimum = 198ms, Maximum = 610ms, Average = 420ms
      420ms is the latency I'm talking about.
      If I ping the satellite office it's
      Packets: Sent = 16, Received = 16, Lost = 0 (0% loss),
      Approximate round trip times in milli-seconds:
      Minimum = 68ms, Maximum = 158ms, Average = 78ms

      If I ping the sattelite office from main office internal, I get this
      Ping statistics for
      Packets: Sent = 14, Received = 14, Lost = 0 (0% loss),
      Approximate round trip times in milli-seconds:
      Minimum = 124ms, Maximum = 745ms, Average = 473ms

      If I ping PDC from BDC sattelite office internal I get this
      Ping statistics for
      Packets: Sent = 20, Received = 19, Lost = 1 (5% loss),
      Approximate round trip times in milli-seconds:
      Minimum = 99ms, Maximum = 705ms, Average = 400ms

      Both servers show almost nil network and CPU utilisation

      Network also suggested enabling QOS on routers.

      so where to go from here?


      • #4
        Re: Latency on Cisco routers

        I would ignore any ping statistics from home as that doesn't matter (IMHO) and is likely to vary widely. The important statistics are the site to site ping times, which are horrendous. IMHO enabling QOS will at best mask the underlying problem and is not likely to actually make any improvements anyway. You have to find out why the ping times are so high. I would reccomend pinging from one DSL modem/router to the other to check the ping times so that you can rule out any internal issues as the cause, this way you're testing just the link between the offices and not getting any erroneous results do to internal issues that may be skewing the results. If the ping times from DSL modem/router to DSL modem/router are as high as the results you've already gotten then you can focus on the DSL connection as being the root of the problem.

        Also try plugging a computer directly in to the LAN port of the DSL modem/router and run pathping to the other DSL modem/router and see what the results are. Pathping is a combintation of ping and traceroute and will give you latency and packet loss statistics for each hop between the two offices.

        The TS sessions are not the cause of the problem here, they are just making the problem worse. The real problem is the latency between the sites.


        • #5
          Re: Latency on Cisco routers

          >I would ignore any ping statistics from home as that doesn't matter (IMHO) and is likely to vary widely.
          generally I agree with you but I test the link from home regularly so I've got a baseline to work from.
          I've contacted ISP to check line and will follow up with your recommendations tomorrow.


          • #6
            Re: Latency on Cisco routers

            This forum rocks!
            I got the ISP to reset the port at the exchange, bingo fixed.
            Which is great but dissappointing that the two different network guys I got in to look at the problem didn't ascertain this. I bet they'll still be charging me
            No one however can give me a reason as to why it happened.


            • #7
              Re: Latency on Cisco routers

              Glad to hear you got it worked out and thanks for posting back.

              I always try to isolate each component of a problem and rule each one out one by one. I try to start "on one end" and work my way to the other and somewhere in between I'll find the cause. Your action of getting the ISP to check/test the actual line/port was the right way to go. Well done.

              Maybe the network guys you hired should be paying you.