FastEther Channel (FEC) is a Cisco method that bundles 100 Mbps FAST ETHERNET ports into a logical link. Because any redundant paths between two switches mean some ports will be in a blocking state and bandwidth will be reduced, Cisco developed FEC to maximize bandwidth use. Figure 2-4 displays a switched network with two 100-Mbps connections between them. Because of STP, the link will be in a blocking state after the election of a root bridge, Switch A, in this case. Switc..
Multicast routing is not supported on Cisco routers by default. Use the following command to enable multicast routing in global configuration mode: Router(config)#ip multicast-routing
Like an OSPF designated router (DR), an IS-IS DIS exists to simulate a point-to-point topology across a multipoint environment. Because of this, a DIS is sometimes called a pseudonode. Despite their similarities, the IS-IS DIS is subtly different from OSPF. The DIS exists separately at Level 1 and Level 2, and there is not a backup DIS. An OSPF DR is elected for life; IS-IS allows preemption if another router comes on line with a higher priority. Fewer adjacencies are..
As discussed earlier, link-state protocols maintain information received from neighbors. Any information received from a neighbor is maintained in a database. Because link-state protocols require the information to be constant among neighbors, IS-IS has different protocol packets. Essentially, IS-IS has four packet types: Hello packets LSPs CSNP data units PSNP data units Each of these is discussed in more detail in the following sections. &nb..
Comparison of the OSPF Restart Mechanisms
The two approaches share many similarities, including the following: • Both have the goals of retaining adjacencies with neighbors and continuing to forward across the restart. • Both require protocol extensions. • Both require support from neighbors. • Both can be used for unplanned and planned restarts. In terms of mechanics, however, these restart approaches differ significantly, as follows: ..
