Dell Force10 E600i FTOS Version 8.4.1.5 Configuration Guide for ExaScale - Page 664

www.dell.com | support.dell.com Each router link is defined as one of four types: type 1, 2, 3, or 4. The LSA includes a link ID field that identifies, by the network number and mask, the object this link connects to. Depending on the type, the link ID has different meanings. • 1: point-to-point connection to another router neighboring router • 2: connection to a transit network IP address of Designated Router • 3: connection to a stub network IP network/subnet number • 4: virtual link neighboring router ID Virtual Links In the case in which an area cannot be directly connected to Area 0, you must configure a virtual link between that area and Area 0. The two endpoints of a virtual link are ABRs, and the virtual link must be configured in both routers. The common non-backbone area to which the two routers belong is called a transit area. A virtual link specifies the transit area and the router ID of the other virtual endpoint (the other ABR). A Virtual Link cannot be configured through a Stub Area or NSSA. Router Priority Router priority is the method used by FTOS to "rate" the routers. Priority is a numbered rating 0-255. The higher the number, the higher the priority. By default, the OSPF router with the highest priority is selected as the DR. The OSPF router with the second highest priority is selected as the BDR. For example, in Figure 35-3, Router 1 with priority 200 is the DR and Router 2 with priority 180 is the BDR. If Router 1 fails, Router 2 would be elected DR and Router 4 would become the BDR. Figure 35-3. Priority and Costs Example Router 2 Priority 180 Cost 50 Router 3 Priority 100 Cost 25 Router 1 Priority 200 Cost 21 Router 4 Priority 150 Cost 20 Router 1 selected by the system as DR. Router 2 selected by the system as BDR. If R1 fails, the system subtracts 21 fromR1 s priority number. R1 s new pirority is 179. R2 as both the selected BDR and the now-highest priority, becomes the DR. If R3 fails, the system subtracts 50 fromits priority. R2 s new priority is130. R4 is now the highest priority and becomes the DR. 664 | Open Shortest Path First (OSPFv2 and OSPFv3)