1

Reminding - ARP Two machines on a given network can

communicate only if they know each other’s physical network address

ARP (Address Resolution Protocol) serves for mapping from high-level IP address into low level MAC address.

2

Reminding – ARP

10.4.10.91

00:11:22:33:44:55:bc

ARP Request (10.4.10.90)

ARP Response (00:11:22:33:44:55:12)

10.4.10.90

00:11:22:33:44:55:12

10.4.10.20

00:11:22:33:44:55:6b

10.4.10.23

00:11:22:33:44:55:40

10.4.10.86

00:11:22:33:44:55:2e

3

Proxy ARP Proxy ARP (also called promiscuous ARP

or ARP hack) is a technique used to map a single IP network prefix into two physical addresses. Using the same network address space for

more than one physical address Assume that there are 2 networks A and

B connected by router R that runs Proxy ARP

Using Proxy ARP, R can use the same net id for both networks.

4

Proxy ARP

.

R

PPP

Network A: 10.10.1.x/24

Network B:

10.10.1.x/24

10.10.1.5

10.10.1.3 10.10.1.4

5

Proxy ARP Router R replies to ARP requests that are

generated by hosts on the PPP connection (Network B), in which the target IP is on network A, namely it sends its MAC address. R know which hosts are connected through the

PPP. These host assume that the destination

host are on the same physical network. In their ARP table the router MAC address is

associated with the destination IP address.