cisco books for ccna

cisco books for ccna.Each of these two links carries half of the traffic, resulting in congestion on the 256kbit/s link. Therefore, always remember to use the command bandwidth, introduced in Chapter 15, to modify the bandwidth of the interface.Authentication H Tag 19.0219.2 How 0SPF worksAs mentioned earlier, OSPF is a link-state protocol. Chapter 15 provides a general introduction to link-state protocols, but each link-state protocol (such as OSPF and IS-IS) has its own unique functions and features. This section describes how single-area OSPF works.19.2.1 Identifying RoutersEach router in an OSPF network must have a unique ID - an ID that is not only unique within the region, but is also independent throughout the OSPF network. All OSPF messages generated by a router contain its ID o The router ID is selected using one of the following.. Manually specifying the router ID for the routing protocol;. Using the maximum IP address of the active loopback interface (which is a logical interface for the router) .. If there is no loopback interface with an IP address configured, use the maximum IP address of the active interface at the time the router boots. The subnet mask of the loopback interface is usually the host mask (/32). Cisco supports the use of other subnet masks for loopback interfaces, but many vendors allow only the subnet mask /32 for loopback interfaces. the router uses the router ID to advertise itself to other routers in the network. As mentioned earlier, this ID must be unique. If no loopback interface is configured, the router will use the maximum IP address of the active physical interface as the router ID. you can also specify the router ID manually, which ensures that the router ID is fixed, regardless of which interfaces the router contains. If there is no active interface, the OSPF process will not start.Therefore there will not be any OSPF routes in the routing table. The loopback interface is always enabled, so it is highly recommended that you use it so that the router can obtain a router ID and enable OSPF.