Address Resolution Protocol; Setting The Arp Timeout; Table 37: Address Resolution Protocol - Edge-Core ECS4810-12M Layer 2 Management Manual

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The switch 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 switch (or any

standards-based switch/router), it first looks up the MAC address

corresponding to the destination IP address in the ARP cache. If the

address is found, the switch 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 switch 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:

destination IP address

destination MAC address ?

source IP address

source MAC address

00-00-ab-cd-00-00

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

switch 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.

Use the IP > ARP (Configure General) page to specify the timeout for ARP

cache entries.

"arp timeout" on page 1381

These parameters are displayed:

Timeout – Sets the aging time for dynamic entries in the ARP cache.

(Range: 300 - 86400 seconds; Default: 1200 seconds or 20 minutes)

The ARP aging timeout can only be set globally for all VLANs.

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