OSPF creates a two-level hierarchy of areas. Area zero (also called the backbone area or transit area) is always the central area; all other areas attach to area zero. Area zero forms the top level in the hierarchy and the remaining areas form the bottom level of the hierarchy. This hierarchical design supports summarization and minimizes routing table entries. Routers in area zero are called backbone routers. Routers that link area zero and another area are cal..
Packet-switched networks fundamentally differ from circuit-switched networks. As shown in Figure 3-2, a connection must first be established between two end hosts in order for them to communicate in a circuit-switched network. This can be achieved by i n-band signaling (call_setup) within a circuit—in other words, the end host transmits a set of signals that allows the circuit to be extended, hop-by-hop, through the network. Alternatively, as in the case of the Integrated S..
Use the following command to send router log messages to a remote syslog server: Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#logging 172.25.1.1 Router(config)#end Router# Although configuring the router with a static IP address like this is the preferred method of configuring a syslog server, you can also specify a hostname to be resolved: Router#configure terminal Enter configuration commands, one per line.&n..
Authenticating Login IDs from a Central System
When you configure AAA authentication on a router, it starts to ignore the locally configured passwords in favor of those provided by the TACACS+ server. In this example, we have configured the router to consult TACACS+ for both the login and enable passwords. This is a great labor saver because it means that you don't have to reconfigure all of your routers just because you want to change passwords. Instead, because the passwords are stored on a central server, you can chang..
Limiting the Impact of IP Helper Addresses
The ip helper-address command implicitly enables forwarding several different kinds of UDP broadcasts. You can prevent the router from forwarding the unwanted types of broadcasts with the no ip forward-protocol udp configuration command: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#no ip forward-protocol udp tftp Router1(config)#no ip forward-protocol udp nameserver Router1(config)#no ip forward-protocol u..
