LSA Type 3 and Inter-Area Costs
ABRs do not forward type 1 and 2 LSAs from one area to another. Instead, ABRs advertise type 3 LSAs into one area in order to represent subnets described in both the type 1 and 2 LSAs in another area. Each type 3 summary LSA describes a simple vector—the subnet, mask, and the ABR’s cost to reach that subnet, as shown in Figure 10-8. Figure 10-8 Representation of Area 3 Subnets as Type 3 LSAs in Area 0 Example 10-5 focuses on the three subnets inside area 3, looki..
Cisco IOS software release 12.0 made it possible for you to configure a remote router as an EIGRP stub router. Stub routers in EIGRP networks use EIGRP to send limited information between the stub and the core routers. A stub router is typically used on routers to minimize memory and processor utilization; as such it is a good candidate for slow routers with minimal memory. The stub router has only one neighbor, a distribution layer router. The remote router onl..
The maximum number of routes over which IGRP can load balance is set with the maximum-paths paths command. Paths may be any number from one to six in IOS 11.0 and later and any number from one to four in earlier versions. The default for all versions is four. Figure 6.16 shows three parallel paths of varying costs from McCloy to network 172.18.0.0. The network administrator wants to load balance over a maximum of only two of these routes while ensuring that if either of these..
Every number in the decimal number system can be represented using ten symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. You are familiar with these symbols and how to use them to represent a number. For example, when you see the number 123, you know that it represents one hundred and twenty-three. But what are the rules that tell you that the symbols 123 represent one hundred twenty-three? The rule you use is the rule of positional value. Start counting and see what happens: 0 1 2 ..
Data Structures of IP Routing Protocols
As traffic is routed through a network, the routers encountered along the way from the source to the destination need consistency in how they route traffic. For example, if one router selected the best path based on hop count, and another router selected the best path based on a link’s bandwidth, a routing loop could conceivably occur. Fortunately, having a common routing protocol configured on all routers within a topology helps ensure consistency in routing decisions. T..
