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..
IP hosts can use several methods of deciding which default router or default gateway to use— DHCP, BOOTP, ICMP Router Discovery Protocol (IRDP), manual configuration, or even by running a routing protocol (although having hosts run a routing protocol is not common today). The most typical methods—using DHCP or manual configuration—result in the host knowing a single IP address of its default gateway. Hot Standby Router Protocol (HSRP), Virtual Router Redundancy Protocol..
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 ..
The IEEE defines VLANs as a group of devices participating in the same Layer 2 domain. All devices that can communicate with each other without needing to communicate through a router (only use hubs/repeaters and bridges, real or virtual) share the broadcast domain. The Layer 2 internetworking devices move frames through the broadcast domain by examining the destination MAC address. Then, by comparing the destination address to a table, the device can determine how to forward..
The service timestamp global configuration command enables timestamps on debug and logging messages. Use the log keyword to turn on time-stamping of log messages: Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#service timestamps log datetime localtime Router(config)#end Router# The command to turn on timestamps for debug messages is similar, but uses the debug keyword: Router#configure terminal Enter configuratio..
