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..
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 ..
IPsec Remote Access and L2L Sessions on the Same Router
Figure 18-3 shows an example network that has both remote access and L2L sessions. In this example, the remote office network is acquiring its address dynamically, via DHCP, from its connected ISP, which also is true of the remote access clients. Because the central office router doesn't know the remote office router's IP address, you would have to configure the pre-shared key for the router as 0.0.0.0 0.0.0.0 with no XAUTH. However, doing this would cause XAUTH to not work f..
SDLC is a serial protocol that is commonly used for SNA devices. It is extremely popular in financial environments for devices such as banking machines, card readers, and account printers. Using SDLC in conjunction with DLSw is becoming increasingly common in these sorts of situations. This allows the remote SDLC devices to communicate with the Token Ring Interface Coupler (TIC) on a mainframe computer through an IP network. There is a huge advantage to this because it means ..
Before moving on to discuss how to influence route choices by changing the OSPF interface costs, first take a moment to consider the CPU-intensive SPF work done by a router. SPF does the work to piece together topology information to find all possible routes to a destination. As a result, SPF must execute when the intra-area topology changes, because changes in topology impact the choice of best route. However, changes to Type 3 LSAs do not drive a recalculation of the ..
