RouteExplorer™ Tutorial – Network Planning and Maintenance

Adding a new router or replacing an existing router – how to make surethere will be no disruption to reachability after cutover?

A common problem when adding new routers or replacing anexisting router in a running network is how to see the interaction of the newrouter(s) with existing network, before they are placed in service.  Route Explorer can help.

Figure 1

Figure 1illustrates an OSPF network where two routers (R1, R2) are serving threenetworks (P1, P2, P3). Let us sayR2 needs to be replaced by a new router R3. R3 is connected and brought online, but with very high linkcost metric, to keep traffic from flowing through it. Route Explorer will discover and display all three routersin its topology map. Route Explorer’sList of Prefixes will confirm that all three prefixes are reachable through allthree of the routers. Highlightingprefix routes to P1, P2, and P3 will confirm that the routes flow over R1, andR2 due to their lower cost (10 vs. 65,535).

Next, in Route Explorer’s “what-if” mode, the networkengineer may simulate the commissioning of R3 and decommissioning of R2 bysetting the link metric of R3 to be 10 and marking R2 “down” in RouteExplorer’s database. RouteExplorer will redraw the new highlighted prefix paths over R3.  Route Explorer’s prefix list willverify availability of P1-P3 via R1 and R3 but not R2.  At this point the router R2 may bedecommissioned and R3 brought into service by setting its metric to be 10.

Here is an example. Figure 2shows a multi-area enterprise network monitored by Route Explorer.  One of the core routers, IP address10.0.251.5, is scheduled to be replaced. To monitor a prefix advertised by that router, 172.22.1.0/24, we havehighlighted a path to that prefix from an edge router.

Figure 2

Figure 3shows the final step in the replacement process. The new router, 10.6.251.200 has been installed and broughtonline. Router 10.0.251.5 has beentaken offline and the prefix route goes to the new router. Figure4shows that the prefix is being advertised by both the new and the old router.

Figure 3

Figure 4

This example has shown how Route Explorer can help in thevalidation of new network components installed during maintenance to ensuresmooth operation and minimum down time.

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HOW TO:

1. Open an X Windows or VNC session to the Route Explorer. See Route Explorer User Guide.
2. Click on File->Open Topology
3. Select the topology domain “DemoEnterpriseAMar03a” from menu.
4. Click Open.
5. List Prefixes for a router:
1. Right-Click on the router of interest
2. Click on Prefixes in the resulting popup window
6. Highlight a route by prefix
1. Click Tools->Find Prefix Path…
2. Enter source router IP address
3. Enter destination prefix

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