Cisco (300-420-ENSLD) Exam Questions And Answers page 23

The following statements are correct about the given output:
• Fa0/2 is the root port for VLAN001
• The switch having the 0A61.0015.4D02 bridge ID is the root bridge for VLAN0001
• The switch connected to the Fa0/6 port of SW1 is using its root port
The value in the Role column in the output for VLAN0001 is Root for the Fa0/2 port of SW1. This implies that the Fa0/2 port is a root port. A root port is the port on a non-root bridge that has the least cost to reach the root bridge. Every non-root bridge must elect a root port. A root bridge does not have any root ports.
The output for VLAN0121 specifies Desg in the Role column for the Fa0/6 port of SW1. This implies that the Fa0/6 port is a designated port. This means that the switch on the other end is using its root port.
The switch having the 0A61.0015.4D02 bridge ID is the root bridge for VLAN0001. For VLAN0001, the bridge ID of the root and the local switch are different. The bridge ID of the local switch (SW1) is 0F2C.08A1.330E, while the bridge ID of the root bridge is 0A61.0015.4D02. The text Port 1 (FastEthernet0/2) in the Root ID section for VLAN0001 in the output indicates that the root bridge is connected to the Fa0/2 port of the local switch.
The options stating that SW1 is the root bridge for VLAN0001 and that the switch having the 0F2C.08A1.330E bridge ID is the root bridge for VLAN0001 are incorrect. The Bridge ID section in the output for VLAN0001 and VLAN0121 specifies the bridge ID of the local switch. In this case, the bridge ID of the local switch (SW1) is 0F2C.08A1.330E. SW1 is not the root bridge for VLAN001; however, SW1 is the root bridge for VLAN0121.
You can determine if a local switch is the root bridge by any of the following:
• The text This bridge is the root appears in the Root ID section of the output for VLAN0121.
• The bridge IDs in the Root ID and Bridge ID sections of the output are the same.
• All the ports of the local switch are Desg (designated) ports and in forwarding state.
The port Fa0/4 is NOT in a blocking state for VLAN 0121. As indicated in the STS column for Fa0/4 under the section on VLAN 0121, it states that is in an a FWD (forwarding) state.
The STP protocol in use is NOT Rapid Spanning Tree protocol (RSTP). If that were the case, the output would display Spanning tree enabled protocol rstp, rather than Spanning tree enabled protocol ieee. This indicates that IEEE 802.1d is in use.
Objective:
Layer 2 Technologies
Sub-Objective:
Configure and verify spanning tree
Cisco Press > Articles > Network Technology > General Networking > CCNP Exam Prep: Traditional Spanning Tree Protocol
Cisco > Cisco IOS Bridging Command Reference > show spanning-tree

Address Resolution Protocol (ARP) is used by Cisco Express Forwarding (CEF) to build the adjacency table. CEF is the switching method used by Catalyst switches. Unlike traditional multilayer switching (MLS), which merely caches Layer 3 information received when traffic passes through a switch, CEF attempts to optimize the routing process by reindexing the routing table and then building an adjacency table based on the routing table information. The type of MLS performed by CEF is called topology-based switching; traditional MLS is known as route caching, demand-based switching, and flow-based switching.
The routing table is reindexed by using a binary search method. The reindexed routing table is called the forwarding information base (FIB). Reindexing the routing table reduces the amount of time spent searching for an entry within a routing table.
After the FIB is created, an adjacency table is created to map the appropriate Layer 2 next-hop address or addresses to each FIB entry. ARP is used to retrieve the Layer 2 address information. If multiple Layer 2 next-hop addresses are available for an entry in the FIB, then CEF can employ load balancing for packets headed to that destination.
The final result is a single database of routing information (FIB) is built for the switching hardware.
Two extremely useful commands for verifying CEF are:
• show ip cef network address - displays entries in the forwarding information base (FIB)
• show adjacency detail | begin adjacency address - shows information about a specific adjacency in the adjacency table
Both commands are shown below with explanations.
SwitchA# show ip cef 192.168.6.0
192.168.6.0/24, version 302, cached adjacency 192.168.166.5, 0 packets, 0 bytes
Via 192.168.166.5, VLAN 185, 0 dependencies
Next-hop 192.168.166.5, VLAN 185
Valid cached adjacency
Above it can be determined that there is a valid CEF entry for the destination network 192.168.6.0 and that there is a valid cached adjacency to the 192.168.166.5 next hop IP address.
In the command output below, it can be determined that 005565946856 is the MAC address of the 192.168.166.5 next-hop address:
SwitchA# show adjacency detail | begin 192.168.166.5
IP VLAN 185 192.168.166.5(6) 0 packets, 0 bytes
005565946856
Objective:
Layer 2 Technologies
Sub-Objective:
Configure and verify switch administration
Cisco > Cisco IOS IP Switching Configuration Guide, Release 12.4 > Part 1: Cisco Express Forwarding > Cisco Express Forwarding Overview > Cisco Express Forwarding Adjacency Tables Overview
Cisco > Cisco IOS IP Switching Command Reference > show adjacency through show ipv6 cef with source > show adjacency
Cisco > Cisco IOS IP Switching Command Reference > show adjacency through show ipv6 cef with source > show ip cef