IP Tools
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Instruction Manual - NXA-ENET8-POE+
Address Resolution Protocol
If IP routing is enabled, the router uses its routing tables to make routing decisions, and uses Address Resolution Protocol (ARP) to
forward traffic from one hop to the next. ARP is used to map an IP address to a physical layer (i.e., MAC) address. When an IP frame
is received by this router (or any standards-based router), it first looks up the MAC address corresponding to the destination IP
address in the ARP cache. If the address is found, the router writes the MAC address into the appropriate field in the frame header,
and forwards the frame on to the next hop. IP traffic passes along the path to its final destination in this way, with each routing
device mapping the destination IP address to the MAC address of the next hop toward the recipient, until the packet is delivered to
the final destination.
If there is no entry for an IP address in the ARP cache, the router will broadcast an ARP request packet to all devices on the
network. The ARP request contains the following fields similar to that shown in this example:
When devices receive this request, they discard it if their address does not match the destination IP address in the message.
However, if it does match, they write their own hardware address into the destination MAC address field and send the message back
to the source hardware address. When the source device receives a reply, it writes the destination IP address and corresponding
MAC address into its cache, and forwards the IP traffic on to the next hop. As long as this entry has not timed out, the router will be
able forward traffic directly to the next hop for this destination without having to broadcast another ARP request.
Also, if the switch receives a request for its own IP address, it will send back a response, and also cache the MAC of the source
device's IP address.
Displaying Dynamic or Local ARP Entries
Use the Tool > ARP page to display dynamic or local entries in the ARP cache. The ARP cache contains static entries, and entries for
local interfaces, including subnet, host, and broadcast addresses. However, most entries will be dynamically learned through replies
to broadcast messages.
Perform these steps to display all dynamic and local entries in the ARP cache:
1.
Click
Tool
>
ARP
.
2.
Select
Show Information
from the Step List.
3.
Click
ARP Addresses
.
Address Resolution Protocol
destination IP address 10.1.0.19
destination MAC
address
?
source IP address
10.1.0.253
source MAC address
00-00-ab-cd-00-00
FIG. 306
Displaying ARP Entries