Jaycee's Networking

May 9, 2009

Ethernet Interface

Filed under: IOS — Tags: — Jaycee @ 3:06 am
interface FastEthernet0/0
 media-type 100BaseX
 mac-adddress 0AAA.ABCD.0101
 arp timeout 60
 duplex full
 speed 100

1. By default, the router will usually select the appropriate media type by sending the Ethernet carrier signal when you connect it to another device. FastEthernet modules often include a MII (Media Independent Interface).

2. By default, the router will attempt to detect both duplex and speed on FastEtherent modules.

3. By default, if the router hasn’t seen any traffic from a particular MAC address within 14,400 secs (4 hours), it will flush the entry from its ARP cache. In the following cases, you might want to reduce the ARP timeout period:

a. In many bridged environments, the bridges will remove MAC table entries after a shorter period (such as 10 minutes). If a station has been idle for more than 10 mins, but less than 4 hours, the router will send the packet. However, the bridge must flood all segments with the traffic to find the destination device. It may be more efficient if the router simply sends out a fresh ARP query for the destination. You’ll probably want to reduce your ARP timeout if this is the case.

b. In DHCP, there are so many ARP entries that the ARP cache frequently fills up and the router has to drop entries. You may want to change the ARP timeout since the MAC address associated with a particular IP address changes frequently.

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