RouteExplorer™ Tutorial – Troubleshooting and Diagnostics

Is it a routing problem or is a server down?

The key question that needs to be answered first indiagnosing a reported service outage is whether the problem is in disruptedconnectivity to the server or the server itself is down.  Route Explorer can help you quicklyidentify if it is a routing problem.

 

In a typical trouble ticket, the helpdesk will identify theIP address or domain name of the server that is disrupted. Whether thedestination server is within the IGP domain, within the multi-domain enterprisenetwork but reachable via BGP, or in the Internet, Route Explorer’s prefix listcan quickly tell you if it is still advertised in your network and show you thehighlighted route between the user and the prefix.

 

Figure 1

Figure 1shows how you may find the current path from the router serving the user’sworkgroup to the prefix of the server’s network.  If a path currently exists, it will be shown highlighted inRoute Explorer’s topology map (see Figure2).  Note that this server network isactually connected to two routers for redundancy (detail at the right in Figure2).

 

Figure 2

By contrast, Figure3shows a case when the prefix is NOT reachable – Route Explorer shows nohighlighted path, only the highlighted source router.  Closer examination of the topology map shows that in thiscase, the link from the user’s workgroup router is down (upper-left), leadingto the outage. But the prefix is still available (lower-right).  This indicates that the server is stillup and running, but the problem lies in the user’s workgroup LAN or router.

Figure 3

Next, Figure 4shows another case when the route to the prefix is unavailable.

 

Figure 4

In this case, the route shown is in a different colorindicating that it is an incomplete route.  This route is in fact, a routing loop.  This can be seen from Route Explorer’slist of highlighted paths.  Figure5shows how.  Note that the RouteExplorer shows how each next hop of the route is resolved.  In this case, the loop occurs when theroute follows default (0.0.0.0/0). Our destination prefix is in fact not in the list at all!

    

Figure 5

Close examination of the route in Figure4also reveals that the destination prefix network is in fact not shown in thetopology map.  This means that theserver network was either down or the prefix was withdrawn.  Showing Route Explorer’s list ofprefixes will confirm. See Figure6.

 

Figure 6

This example has shown how Route Explorer can quickly helpyou distinguish a routing failure from a failure in the server network. In thenext example, we show how Route Explorer can help you pinpoint the time andlocation of the failure.  Below, weshow how to put this Route Explorer capability in action in your own network.

HOW TO:

  1. Open an X Windows or VNC session to the Route Explorer.
  2. Open the online topology:
    1. Click on menu Topology->Open Topology…
    2. Select the topology of interest – the online recording topologies will be highlighted in green text
  3. Find Prefix Path:
    1. Click on Tools->Find Prefix Path…
    2. Enter source router IP address or DNS name
    3. Enter destination prefix (IP address/mask or DNS name)
    4. Click OK
  4. List Highlighted Paths:
    1. Click on Tools->List Highlighted Paths
    2. To show the individual segments of all highlighted paths, click “Expand All”.
    3. To see an individual path’s segment details, click “+”.
    4. To clear all highlighted paths from the display, click Tools->Unhighlight All Paths in the path list window or click Unhighlight All Paths in the path list window.
  5. List prefixes:
    1. Click on Tools->List Prefixes
    2. To see only the prefixes by a routing protocol (IGP or BGP),

                                                    i.     selectfrom the drop-down menu Filter->Protocol

                                                     ii.     clickon the radio button for the desired protocol

                                                       iii.     clickShow

    1. Many other filter criteria are available from the drop-down menu, including IGP prefix type, BGP next-hop, BGP attributes (MED, Local Pref), etc.

 

 

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