arp
Display and modify ARP cache entries
TLDR
Show the current ARP table
Show [a]lternative BSD style output format with on fixed columns
[d]elete a specific entry
[s]et up a new entry in the ARP table
SYNOPSIS
arp [-vnN] [-H hwtype] [-i if] [-a] [hostname]
arp [-vwnD] [-i if] [-c addr] hostname
arp -d hostname
arp -s hostname hwaddr [temp] [pub]
arp -f filename
PARAMETERS
-a, --display
Display or dump kernel ARP table (default).
-d, --delete hostname
Delete ARP entry for hostname (IP or name).
-D, --use-device
Use hardware address from specified device.
-i if, --device if
Operate on specific network interface.
-v, --verbose
Enable verbose output.
-n, --numeric
Show numeric addresses, skip hostname resolution.
-s hostname hwaddr, --set
Create permanent (static) ARP entry.
-S hostname hwaddr netmask masklen, --publish
Create proxy ARP entry with publish flag.
-f filename
Load ARP entries from file (like /etc/ethers).
-H type, --hwtype type
Override hardware type (e.g., ether).
-c addr, --create addr
Create new entry if absent.
-N, --no-nameres
Suppress name resolution in some modes.
DESCRIPTION
The arp command views and modifies the kernel's Address Resolution Protocol (ARP) cache, which maps IPv4 addresses to MAC hardware addresses on local networks. ARP enables efficient Layer 2 communication by caching resolutions, avoiding broadcasts for each packet.
Default operation (arp or arp -a) lists all entries in the cache, showing IP, MAC, interface, and type (dynamic/static). Users add permanent entries with -s for reliability or security (e.g., preventing ARP spoofing), delete with -d, or manage proxy ARP for routing scenarios. Options filter by interface (-i), suppress DNS resolution (-n), or enable verbose output (-v).
Essential for network diagnostics, verifying connectivity issues, or static configurations in environments without DHCP. Part of net-tools, it works on IPv4 only. Output resembles: 192.168.1.1 (MAC_ADDRESS) at interface [ether] on dev eth0.
CAVEATS
Deprecated; use ip neigh from iproute2. IPv4-only, requires root for modifications. Static entries survive reboots only if in /etc/ethers or systemd-resolved.
EXAMPLES
arp -a
Show all entries.
arp -n -i eth0
Numeric list for eth0.
arp -s 192.168.1.100 00:11:22:33:44:55
Add static mapping.
arp -d 192.168.1.100
Remove entry (needs sudo).
FILE FORMAT
For -f: IP_address hardware_address [type], e.g.,
192.168.1.1 00:11:22:33:44:55
HISTORY
Part of net-tools since early 1990s Linux (BSD heritage). Peaked in 2000s usage; deprecated post-2010 as iproute2 (ip neigh) standardized around Linux 2.6 kernels.
