Cisco ARP

Using the Address Resolution Protocol (ARP) we can discover the link layer address (MAC Address) associated with an IPv4 address on Cisco routers and switches.

R1#show arp 
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.10.1            -   0c64.2b8d.2200  ARPA   GigabitEthernet0/0
Internet  192.168.10.2           18   0c64.2bed.8a00  ARPA   GigabitEthernet0/0
!
R2#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.10.1           18   0c64.2b8d.2200  ARPA   GigabitEthernet0/0
Internet  192.168.10.2            -   0c64.2bed.8a00  ARPA   GigabitEthernet0/0
arp
arp
R1#show ip int brief
Interface                  IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0         192.168.10.1    YES NVRAM  up                    up      
GigabitEthernet0/1         unassigned      YES NVRAM  administratively down down    
GigabitEthernet0/2         unassigned      YES NVRAM  administratively down down    
GigabitEthernet0/3         unassigned      YES NVRAM  administratively down down    
!
R2#show ip int brief 
Interface                  IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0         192.168.10.2    YES NVRAM  up                    up      
GigabitEthernet0/1         unassigned      YES NVRAM  administratively down down    
GigabitEthernet0/2         unassigned      YES NVRAM  administratively down down    
GigabitEthernet0/3         unassigned      YES NVRAM  administratively down down    
!
!
R1#ping 192.168.10.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.10.2, timeout is 2 seconds:
!!!!!
!
R2#ping 192.168.10.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.10.1, timeout is 2 seconds:
!!!!!

 

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