- Fact:
- The mapping between IP addresses and Physical (e.g., Ethernet) addresses can change over time
- Reasons that can cause
a change:
- A node can
change its
physical address:
- A node might experience a hardware failure and needs a new network card
- More common:
a node can
change its
logical (IP) address:
- When a node (computer) is rebooted, it can receive a different IP addresses
- A node can
change its
physical address:
- Fact:
- If the physical address
or
the logical (IP) address
is changed, then:
- The ARP mapping will be incorrect (mapping error)
Example:
- Before the
node y9 has
physical
address EA9:
- After the node
is rebooted, it is
given the
IP address y13:
Result:
- IP packet destined for
y9 will
not be
accepted by
the new configuration !!!
(Because the IP packet has a wrong destination IP address !!!)
- IP packet destined for
y9 will
not be
accepted by
the new configuration !!!
- If the physical address
or
the logical (IP) address
is changed, then:
- Fixing the
out-of-date
ARP cache entry problem:
- Each entry in the
ARP table
has:
- a expiration ("aging") time out value
(The time out value is usually several hours)
- Each entry in the
ARP table
has: