Perle Systems P840 User Manual download pdf (Page 3)

Introduction

IP Routing and the P840 Router

The P840 router may be used to route between subnets within the same network or between different networks.

Network broadcasts sent within a subnet-routed environment will not be forwarded to the other subnets in the network.

The procedure for establishing an IP connection through an IP router is explained on the next few pages.

ARP—Address Resolution Protocol

A protocol called ARP (Address Resolution Protocol) is used to determine the MAC address of a particular IP address. The

MAC (Medium Access Control) address is unique predefined number for each device on the LAN. The manufacturer of the

device assigns MAC addresses. The IP address for each device is assigned by the network administrator according to the

network structure.

If the originating station does not know the MAC address of the destination station, a MAC broadcast will be transmitted

onto the LAN asking “Who has IP address 170.22.10.4?” This MAC broadcast is called an ARP request. Because the ARP

request is a MAC broadcast, every device on the LAN will see the frame. The device that has the IP address 170.22.10.4 will

respond with a frame to the originating station. The ARP reply frame will include the MAC address of the destination device.

Now when the two devices wish to send data across the LAN to each other, they will both use the MAC and IP address of

the other device.

Each device on the LAN maintains a table for MAC addresses and IP addresses called the ARP cache. The ARP cache

contains a list of IP addresses and their corresponding MAC addresses.

Proxy ARP

Each time an originating station does not know the MAC address of a destination station, the originating station sends out an

ARP request. If the destination station is on a different network, the router connected to the originating network will see the

frame and look at the IP address being requested. The router will look in its routing table to see if it has an entry for that IP

network address. If the router has an entry, the router will generate an ARP reply to send back to the originating station. The

ARP reply will specify the MAC address of the router as the MAC address to send frames to for the IP address of the

destination station.

1 2 3 4 5 6 7 8 ... 57 58

No comments

Perle Systems P840 User Manual Page 3