arp aging time on router and mac address aging time on switches set close t

[christina_neo]

Hi,

appreciate some advice on the following:

what is the benefit of setting arp aging time on router and mac address aging time on switches close to each other?

Thanks,

Christina

[Roberto Salazar]

If the switches are flooding unicast packet to all the ports when the cam ages out normally due to assymetric routing/path making the cam or mac address aging time and the arp time out close to each other helps. If there are no such issue, it serves no benefit at all.

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[christina_neo]

Hi,

based on the below output, do you think implementing it will benefit? Thanks.

C2950#sh int fa0/43

FastEthernet0/43 is up, line protocol is up (connected)

Hardware is Fast Ethernet, address is 000d.5e11.4e2b (bia 000d.5e11.4e2b)

MTU 1500 bytes, BW 100000 Kbit, DLY 1000 usec,

reliability 255/255, txload 7/255, rxload 2/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s

input flow-control is off, output flow-control is off

ARP type: ARPA, ARP Timeout 04:00:00

Last input never, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 933000 bits/sec, 149 packets/sec

5 minute output rate 2981000 bits/sec, 263 packets/sec

2819781393 packets input, 3782332886 bytes, 0 no buffer

Received 266693 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 0 multicast, 0 pause input

0 input packets with dribble condition detected

4015025747 packets output, 2328228393 bytes, 0 underruns

0 output errors, 0 collisions, 2 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

C2950#

[Roberto Salazar]

The output does not really tell us anything. Are you seeing unicast traffic on a port where it should be going? that would mean unicast getting flooded to ports. If you are not sure and you have no measurable performance impact, there is no need to adjust the cam/mac-address table aging timeout.

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