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IP Configuration 279
Notice that the configuration matches the output of the show interface, show ip interface, and
show interface ip brief commands. For instance, in Example 5-3, the IP addresses in the
configuration match the output of show ip interface brief. If these details did not match,
one common oversight is that you are looking at the configuration in NVRAM, not in RAM.
Make sure to use the show running-config or write terminal commands to see the active
configuration.
The subnet mask in the output of show commands is encoded by numbering the network and
subnet bits. For example, 10.1.4.0/24 means 24 network and subnet bits, leaving 8 host bits with
this subnetting scheme. The terminal ip netmask command can be used to change this
formatting, as seen in Example 5-2.
Example 5-4 shows the ARP cache generated by the show ip arp output. The first entry shows
the IP address and MAC address of another host on the Ethernet. The timer value of 0 implies
that the entry is very fresh--the value grows with disuse. One entry is shown for the router's
Ethernet interface itself, which never times out of the ARP table.
The debug ip packet output in Example 5-4 lists one entry per IP packet sent and received. This
command is a very dangerous command--it could crash almost any production router due to
the added overhead of processing the debug messages. Notice that the output shows both the
source and destination IP addresses.
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
Seville#show ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.1.3.102 0 0060.978b.1301 ARPA Ethernet0
Internet 10.1.3.253 - 0000.0c3e.5183 ARPA Ethernet0
Seville#debug ip packet
IP packet debugging is on
Seville#ping 10.1.130.251
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.130.251, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 80/81/84 ms
Seville#
00:09:38: IP: s=10.1.130.251 (local), d=10.1.130.251 (Serial1), len 100, sending
00:09:38: IP: s=10.1.130.251 (Serial1), d=10.1.130.253 (Serial1), len 100, rcvd 3
00:09:38: IP: s=10.1.130.253 (local), d=10.1.130.251 (Serial1), len 100, sending
00:09:38: IP: s=10.1.130.251 (Serial1), d=10.1.130.253 (Serial1), len 100, rcvd 3
00:09:38: IP: s=10.1.130.253 (local), d=10.1.130.251 (Serial1), len 100, sending
00:09:38: IP: s=10.1.130.251 (Serial1), d=10.1.130.253 (Serial1), len 100, rcvd 3
00:09:38: IP: s=10.1.130.253 (local), d=10.1.130.251 (Serial1), len 100, sending
00:09:38: IP: s=10.1.130.251 (Serial1), d=10.1.130.253 (Serial1), len 100, rcvd 3
00:09:38: IP: s=10.1.130.253 (local), d=10.1.130.251 (Serial1), len 100, sending
00:09:38: IP: s=10.1.130.251 (Serial1), d=10.1.130.253 (Serial1), len 100, rcvd 3
Seville#
Example 5-4
Seville Router Configuration and EXEC Commands (Continued)
ch05.fm Page 279 Monday, March 20, 2000 5:06 PM