Timothy, A follow-up question or two. I have noticed that, for years, it is impossible to ping our server from the outside. I think (but am not sure of this) that pinging is disabled at the router. I don't know if it came that way, or if it was disabled by the previous system administrator. Anyway, how do I turn it back on? (Of course, it might be being disabled in ISA server as well.) Rod > -----Original Message----- > From: "Timothy Mangan" <tmangan@xxxxxxxxxxxx> > Subject: [windows2000] Re: Need some basic instruction in networking > Date: Sat, 8 Nov 2003 14:37:48 -0500 > > [NOTE: Long Response] > 1) What is a CSU/DSU? > A CSU/DSU is a layer 1 conversion device. It takes a serial interface > cable > (coming out of the router) and converts it to a synchronized 1.544Mhz > digital signal which is used to send to the telco CO. The CSU/DSU will > always have information about the quality of the line between the CSU/DSU > and the CO (often called "the local loop"). If you call the CO they will > test out the local loop remotely. They can either read the registers > remotely or run a "CSU loopback test". If you complained and they said > they > tested the line, this has been done and the line is OK. Pin-outs for T1 > cables are different. If you want to replace those cables, get a T1 > replacement. Belden makes them, as do others. > 2) Where else can the problem be? > In logical order: In-house LAN, Router, Router to CSU/DSU, Local loop, > the > backbone (Internet?), and repeat at the far end. You want to isolate out > portions of the problem. For example, that CSU loopback I mentioned > earlier. > - To eliminate the "in-house LAN", work from router to router (the router > closest to the T1 at each site). You are probably using Cisco Routers. > Find someone with a password and log in (you can usually telnet in, > otherwise there will be a console port). You can ping the ip address of > the > router at the far end (as well as traceroute, although that is blocked in > the internet backbone much today). If the round trip delay between > routers > is reasonable (eg under 300ms), then the WAN is OK and the problem will be > in-house. > > Often, the problem is in the local loop or the backbone, and the following > applies if that is the case. You should be able to ping your ISP gateway > and watch delay time there. Most of the delay should occur in the local > loop (as the speeds are slower). Sometimes it happens between carriers in > the backbone. You might have Quest as the ISP at both ends, but typically > the traffic will be carried over someone else in-between (companies like > Global Crossing). The interfaces between carriers will clog up sometimes > when they need to add a new interface to handle increased capacity. When > this happens, the local ISP might say "my network is OK". If you are in > this situation -- especially if you use the same ISP at each end -- you > want > to ask them to measure the delay between the two gateway routers (the > first > router in the ISP attached to each site). Ask them for a round trip delay > number. > - You can turn on a "DSU loopback" in the CSU/DSU as well. This is a > loopback that sends data sent by the router back to itself. If that > loopback is enabled and the router sees itself (you have to be logged into > the router to see this), you have proved out the serial cable between the > two. > > Hopefully this can help. > > Timothy R. Mangan - Founder, TMurgent Technologies > tmangan@xxxxxxxxxxxx www.tmurgent.com (+1)781.492.0403 ******************************************************** This Weeks Sponsor Pearl Software Internet Monitoring, Filtering, and Control Solutions Enabling User & Group Level Oversight & Access Policies Fully Functional in a Thick or Thin Client Environment http://www.pearlsw.com ********************************************************** To Unsubscribe, set digest or vacation mode or view archives use the below link. http://thethin.net/win2000list.cfm