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Privileged EXECDomain 1.0 / 3.0
show ip arp
Displays the router's ARP cache. This table maps known Layer 3 IPv4 addresses to their corresponding Layer 2 hardware MAC addresses. Before a router can encapsulate an IP packet into an Ethernet frame to send it across a local link, it MUST have an entry in this table.
Quick Reference
Execution Mode
Router#Target ProtocolARP (Address Resolution Protocol)
Default Timeout4 Hours (240 Minutes)
Wipe Table Command
clear ip arpReading the Output
Router# show ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 192.168.1.1 - aaaa.bbbb.cccc ARPA GigabitEthernet0/0
Internet 192.168.1.50 12 1111.2222.3333 ARPA GigabitEthernet0/0
- Age (min) "-" : A hyphen means the router owns this IP address. It is bound to a local interface and will never expire.
- Age (min) "12" : This is a dynamic entry learned from a neighboring device 12 minutes ago. If it hits 240 minutes without activity, it gets deleted.
CCNA Exam Gotchas
[!]
Incomplete ARP Status
If you ping an IP address and check the ARP table, you might see Incomplete listed under the Hardware Addr column. This means the router sent out an ARP broadcast ("Who has 10.1.1.5?"), but no device ever replied. This usually points to a dead host, a bad cable, or an aggressive host firewall dropping ARP replies.