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I'm trying to learn the ARP protocol. My idea about ARP is that it is a protocol that help addressing the IP to the exact MAC Address.
But when I try to do:
arp -a
Which I think it will show the list of IP addresses and the matching MAC addresses. I understand everything until I see the word permanent. The other lines are marked ifscope, and one is marked permanent.
Can someone tell me what mean permanent? Why is this line different?
Thanks in advance.
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Address Resolution Protocol (ARP) is a protocol that associates the IP address with the MAC address of a network device. A static ARP entry is a permanent entry in your ARP cache.
The output from arp -a will list the network interface, target system and physical (MAC) address of each system. Other addresses may be static as well as the one indicated above, but these entries were picked up as a response to network traffic, not statically added to the table through a deliberate arp -s command.
arp -a: This command is used to display the ARP table for a particular IP address. It also shows all the entries of the ARP cache or table. arp -g: This command works the same as the arp -a command. arp -d: This command is used when you want to delete an entry from the ARP table for a particular interface.
Specifies the type of hardware address. If the address type is specified when invoking arp from the command line, it should not be specified in the file entries. Otherwise, it should be specified in each file entry. Valid hardware address types are: ether for an Ethernet interface.
According to the TCP/IP Guide:
There are two different ways that cache entries can be put into the ARP cache:
Static ARP Cache Entries: These are address resolutions that are manually added to the cache table for a device and are kept in the cache on a permanent basis. Static entries are typically managed using a tool such as the arp software utility.
Dynamic ARP Cache Entries: These are hardware/IP address pairs that are added to the cache by the software itself as a result of successfully-completed past ARP resolutions. They are kept in the cache only for a period of time and are then removed.
So the word permanent in the arp -a output means that the entry is manually added to the cache (static).
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