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TCP/IP Address Resolution Protocol Utility (arp)
(Page 2 of 2)
arp Utility Functions
To allow administrators to manage
this ARP cache table, TCP/IP devices include an arp utility.
It has three basic functions, which are invoked using three different
versions of the command (which, for once, are the same in UNIX and Windows!):
Additional arp Features
- ARP Cache Table Display (arp -a):
When the -a option is used with the utility, it displays
the current contents of the ARP cache table. Each entry in the table
shows the IP address and hardware address pair for one device (interface,
actually); usually an indication is also given as to whether each entry
is static or dynamic
The exact format of the display varies from one implementation to the
next; some programs show IP addresses while others show host names,
and still others may show both. Some systems default to displaying host
names but allow the -n option to also be used to force only
IP addresses to be displayed and not names.
- ARP Cache Table Entry Addition (arp
-s <host-name> <hw-addr>): This syntax allows
an administrator to make a new manual ARP cache table entry that maps
the given host name to the specified hardware address.
- ARP Cache Table Entry Deletion (arp
-d <host-name>): This command removes the specified
cache entry from the table. Some implementations allow the addition
of another parameter to specify that all entries should be removed from
Certain versions of the software
may also supplement these basic commands with additional features. One
common additional option on UNIX systems is the ability to specify a
file from which cache table entries may be read, using arp -f
<file-name>. This saves a considerable amount of time and
effort compared to typing each entry manually using arp -s.
Note also that access to options
that cause the ARP cache table to be changed may be restricted by the
operating system to only authorized users. This is especially true of
the delete function, and especially especially true of the function
that allows the entire ARP table to be deleted. J
Key Concept: The TCP/IP arp utility is used by an administrator to inspect or modify a hosts ARP cache table, which contains mappings between TCP/IP host names and IP addresses.
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Version 3.0 - Version Date: September 20, 2005
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