RouteExplorer™ Tutorial – Network Planning and Maintenance

Which secondary path does a route follow in the event of a link failure?

Many network design tasks require knowing the alternatepaths in the event of link failures, for an end-to-end service path such anMPLS tunnel, routes to a disaster recovery SAN, or a VoIP path.  Traditional network design tools sufferfrom lack of dynamic and real-time knowledge of the network – their path asindicated in the simulated design of the network is likely to be out-of-syncwith the network as it is running right now.  Ping and Traceroute tools give information about the currentpath but do not allow playing out a hypothetical link down scenario. RouteExplorer quickly and easily lets the user see this and other scenarios.

 

There are two ways to highlight a path in Route Explorer’sdatabase – by “point-and-click” on source and destination routers in thetopology map itself or by specifying a destination prefix and sourcerouter.  The route highlighted maybe as it is right now, or at any time in the past in the recorded history ofthe topology (for forensic diagnosis or historical path performance analysis).

 

Figure 1

To highlight a route by point-and-click, right click on thesource router.  A popup menu willbe displayed with the node information. See Figure 1.  Click on “Route Source”.  The source router will be highlightedin yellow.  Next, right click onthe destination router and click on “Route Destination” in the resultingpopup.  See Figure2.The entire route will be highlighted in yellow.  See Figure 3.

 

 

Figure 2

 

Figure 3

To see the route in detail, select Tools->ListHighlighted Paths menu item.  RouteExplorer will display a list of each hop in the route, including the linkmetric, protocol, and how the next hop was resolved.  Click on any row in the table to highlight that hop in thetopology map.  See Figure4.

 

Figure 4

To highlight a path from a source router to a destinationprefix, click on Tools->Find Prefix Path…  A popup window will be displayed.  Enter the source router address and destination prefix inthis window. See Figure 5.

 

   

Figure 5

The path will be highlighted in the topology map inyellow.  The list of highlightedpaths can provide details of the hops. Note that in this example, the prefix is an external domain (www.nytimes.com).  Route Explorer’s multi-protocol routing analysis capabilityenables it to find the exit router and highlight the path using both IGP andBGP protocols. See Figure 6.

Figure 6

Having thus highlighted a path in Route Explorer, linkfailure analysis is now possible. To simulate the failure of any particular link in the highlighted path,simply right click on the link itself in the topology map.  A popup menu will be displayed showingthe details of the link.  See Figure7.

 

Figure 7

Click on “Down”. The link will be shown in red and the highlighted path will be redrawnto the next best route.  In thisinstance, at the cost of one extra hop. See Figure 8.  The list of highlighted paths will showthe extra hops when you click “Reload”. A list of “edited” links can be shown by clicking Tools-> Show Router/ Link Edits.  See Figure8at the bottom right.

 

Figure 8

To see the effect of the next link failure, see Figure9.  This analysis can be continued on a hopby hop basis to find the best alternate path for this route.

 

 

Figure 9

This note has shown how Route Explorer provides the mostup-to-date routing path information and relevant failure simulation forplanning and configuring service paths in a dynamic routing network.  This unique Route Explorer capabilitycan save hours or days in the design and rollout of new services such as VoIPand MPLS VPNs.

 

HOW TO:

  1. Open an X Windows or VNC session to the Route Explorer.  See Route Explorer User Guide for details.
  2. Click on File->Open Topology
  3. Select the topology domain “DemoTier1ISPJun02a” from menu.
  4. Click Open.
  5. Highlight a route:
    1. Right-click on source router
    2. Click “Route Source” in node pop-up menu
    3. Right-click on destination router
    4. Click “Route Destination” in pop-up
  6. To see the route in hop-by-hop detail, select Tools->List Highlighted Paths
  7. Down a link:
    1. Right-click on link
    2. Click “Down” in link pop-up menu
  8. Show all simulated changes: Select Tools->List Router/Link Edits
  9. Restore edits:
    1. Click on “Restore All” in list of edits
    2. Up the individual links or nodes via pop-up menu (right-click on item)

 

 

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