A
dd
r
ess
R
eso
l
ut
i
o
n
Pr
otoco
l
dd ess eso ut o otoco
(ARP), RFC 826
http://icourse.cuc.edu.cn/networkprogramming/
Oct. 2009
ARP & RARP
ARP & RARP
Note:
The Internet is based on IP addresses
Data link protocols (Ethernet, FDDI, ATM) may have different (MAC)
addresses
addresses
The ARP and RARP protocols perform the translation
between IP addresses and MAC la
y
er addresses
y
We will discuss ARP for broadcast LANs, particularly Ethernet
LANs
Ethernet MAC
ARP
RARP
Ethernet
MAC
address
(48 bit)
ARP
IP address
(32 bit)
Advanced Windows Network Programming
2
2009/10/21
RARP
Problem of mapping
Problem of mapping
The problem of mapping Internet addresses to
physical addresses is known as the address resolution
problem.
Each Ethernet device has its own unique number. Change
the card and you change its physical address.
Physical address are 6 bytes long, too large to multiplex
within an Internet address.
N h b ddd h k h
N
ew
mac
h
ines
can
b
e
a
dd
e
d
to
t
h
e
networ
k
wit
h
no
disruption of service.
Bt ddi ht h ld t i fi i
B
u
t
,
a
ddi
ng
new
h
os
t
s
s
h
ou
ld
no
t
requ
i
re
recon
fi
gur
i
ng
existing hosts to inform them of the new machine.
2009/10/21linwei@cuc.edu.cn
3
Address Translation with ARP
Address Translation with ARP
ARP Request:
A
rgon
broadcasts
an
ARP
request
to
all
stations
on
the
network: “What is the hardware address of 128.143.137.1?”
Advanced Windows Network Programming
4
2009/10/21
Address Translation with ARP
Address Translation with ARP
ARP Reply:
3
Router
1
3
7
responds
with
an
ARP
Reply
which
contains
the
hardware address
Advanced Windows Network Programming
5
2009/10/21
