You know that Router2 is configured for RIP. Which Cisco Internetwork Operating System (IOS) command is used to view the current state of all active routing protocols?
A. show ip arp
B. debug ip rip
C. show ip protocols
D. show ip routing process
E. show arp
F. show interfaces
Correct Answer: C
The show ip protocols command is used to view the current state of active routing protocols. This command is issued from Privileged EXEC mode. The syntax of the command is as follows:
Router2# show ip protocols
Output of the command would resemble the following:
This command shows additional information about individual protocols. The version number of RIP being used is shown on the seventh line of the output. This output also indicates on lines 12-14 that it is routing for three networks: 184.108.40.206, 220.127.116.11, and 10.3.0.0. This means that the router will be sending and receiving RIP updates on any interfaces that have IP addresses in those networks.
Also note that the router at 18.104.22.168 has not sent an update in 3 minutes and 10 seconds. If an update is not received in 50 seconds (for a total of 4 minutes), the route-flush timer (240 seconds from the last valid update) will have expired, causing the local router to remove all networks learned from the router at 22.214.171.124 from the routing table.
For more specific information about those interfaces, in terms such as S0 or Fa0/0, you could execute the show ip interface brief command as shown below. The output displays the addresses of the interfaces, which would indicate which interfaces were enabled for RIP and thus sending and receiving updates.
The show ip arp command is incorrect because this command is executed on a router to determine the IP and MAC addresses of hosts on a LAN connected to the router.
The debug ip rip command is incorrect because this command is used to capture RIP traffic between the routers in real time. This command could also be used to determine the version of RIP being used as shown in line 2 of the partial output of the command below:
Router2#debug ip rip
RIP protocol debugging is on
*Mar 3 02:11:39.207:RIP:received packet with text authentication 234
*Mar 3 02:11:39.211:RIP:received v1 update from 126.96.36.199 on Serial0
*Mar 3 02:11:39.211:RIP: 188.8.131.52/8 via 0.0.0.0 in 2 hops
*Mar 3 02:11:40.212:RIP: ignored v2 packet from 192.168.5.6 (illegal version)
In the above output Router 2 has received a version 1 update from a router at 184.108.40.206 which indicates that a ping to that router should succeed. It also shows what was learned from the router at 220.127.116.11, which is the router to network 18.104.22.168/8 via 0.0.0.0. The 0.0.0.0 indicates that the next hop for that route is the router that sent this advertising (the router at 22.214.171.124).
The output also shows that a RIP router at 192.168.5.6 sent a version 2 update that was ignored by Router 2, which is using version 1. This mismatch of versions will prevent Router 2 from forming an adjacency with the router at 192.168.5.6.
Note: Before running any debug command you should execute the show processes command and verify that the CPU utilization on the router is low enough to handle the effects of running the debug command.
The show ip routing process command is incorrect because it is not a valid Cisco IOS command.
The show arp command is used to identify the IP address to MAC address mappings the router has leaned through the ARP broadcast process. It is helpful when you have identified errors associated with a MAC address and you need to learn the IP address or vice versa. Sample output is below.
router# show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.0.0.3 0 0004.dd0c.ffcb ARPA Ethernet01
Internet 10.0.0.1 – 0004.dd0c.ff86 ARPA Ethernet0
The difference between the show arp command and the show ip arp command is that show arp will also include mappings learned through non-IP protocols such as when inverse ARP is used to learn and map DLCIs to IP addresses.
The show interface command can also be used to identify IP addresses from MAC addresses and vice versa, but also indicates the state of the interface; IP addresses MTU and much more about each interface. Sample output is below.
router# show interfaces
Ethernet 0 is up, line protocol is up
Hardware is MCI Ethernet, address is 0000.0c00.750c(bia 0000.0c00.750c)
Internet address is 10.108.28.8, subnet mask is 255.255.255.0
MTU 1500 bytes, BW 10000 Kbit, DLY 100000 usec, rely 255/255, load 1/255
Compare and contrast distance vector and link-state routing protocols
Cisco > Cisco IOS IP Routing Protocols Command Reference > IP Routing Protocol-Independent Commands: S through T > show ip protocols