RouteExplorer™ Tutorial – Network Planning and Maintenance

Disaster planning – see what effect router failures will have on serviceavailability

Most distributed enterprises have a backbone of IP routersthat is designed to provide continuous service in the event of failures.  But testing this redundancy on a livenetwork is hardly an optimum way to verify availability of services in event ofrouter failure, and testing for “disaster” situations such as the loss of adata center or cascade failures of routers is usually impossible.  Route Explorer provides a very easy andsafe way to check for the availability of routes to vital services in the eventof router failures.

This example shows a multi-area OSPF network of a globalenterprise with a backbone of three highly connected core routers.  See Figure1.

Figure 1

To see the effect of a core router failure, let us firsthighlight several representative prefix paths spanning this network. Thesecould be prefixes to business critical services such as application servernetworks. We have highlighted 3such prefix paths in Figure 2.

Figure 2

To simulate the effect of a down router in Route Explorer,simply right click on the router (see Figure3)and click “Down”. Note that thecore router in this example is in four different OSPF areas.  Route Explorer gives the user theflexibility to down the router in each area separately.

Figure 3

Figure 4shows the effect on the prefix routes we highlighted earlier. Note that two ofthe routes were rerouted to a second core router. Route Explorer’s List of Highlighted Paths shows the detailsof each route including each hop and it’s metric.

Figure 4

Let us now examine the effect of a second routerfailure. Cascading router failuressometime occur as a result of traffic suddenly being rerouted from a primaryrouter to a secondary. Figure5shows the result on our selected routes. All three routes are still reachable via the remaining core router.

Figure 5

Even in the most redundant and well-designed networks, RouteExplorer can provide the level of confidence from verification of prefixreachability in a “disaster”, without the disaster.

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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 an online topology (shown in green) and click Open.
4. 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
5. To see the route in hop-by-hop detail, select Tools->List Highlighted Paths
6. Down a router:
1. Right-click on a router
2. Click “Down” in node pop-up
7. Show all link/router simulated changes: Select Tools->List Router/Link Edits
8. 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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