Avoiding Routing Loops When Redistributing
Routing loops occur when a routing protocol redistributes routes into another protocol and then receives the same routes back—a process called route feedback. Because the metric is reset through redistribution, the routing protocol could see the redistributed path as more attractive. The potential for confusion is enormous, as shown in Figure 11-3; routes distributed from OSPF to EIGRP are distributed back to EIGRP at two redistribution points, causing the routing tables of..
Propagating LSPs on a Broadcast Link
A psuedonode on a broadcast link may need to send out both Level 1 and Level 2 updates. It sends these updates, using multicast MAC addresses, to all Level 1 routers and all Level 2 routers. Because the pseudonode is just that—a pretend system—a real node or system must enter the charade and perform the tasks of the pseudonode. The designated intermediate system (DIS) takes on much of the responsibility for synchronizing the databases on behalf of the pseudonode (recall t..
Routers cannot simply use logic by which they receive a multicast packet and then forward a copy of it out all other interfaces, without causing multicast packets to loop around the internetwork. To prevent such loops, routers do not forward multicasts out the same interface on which they were received. Multicast routers use a reverse-path-forwarding (RPF) check to prevent loops. The RPF check adds this additional step to a dense-mode router’s forwarding logic: Look at the ..
Catalyst Image File Management
As with routers, Catalysts need software to function. The software loads into the flash memory of the Supervisor module and is referred to as the Supervisor Engine Software. The software provides the Catalyst CLI, Spanning Tree functions, VLAN configurations, VTP, and many other processes associated with the Supervisor. The Catalyst 5000 Supervisor I and Supervisor II modules differ in how they transfer software images compared to the Supervisor III module. Therefore, they a..
The AAA Accounting feature allows you to capture keystrokes and log them on the TACACS+ server: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z.Router1(config)#aaa new-model Router1(config)#aaa accounting commands 1 default stop-only group tacacs+Router1(config)#aaa accounting commands 15 default stop-only group tacacs+Router1(config)#endRouter1# The ability to capture every keystroke entered into a router is a powerful security a..
