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Webcast-Catalyst9k
New Member

losing arp record

Hi!

I have some static nat translations in my cisco2620 like following:

ip nat inside source static tcp 192.168.10.33 25 195.136.125.33 25

ip nat inside source static tcp 192.168.10.34 25 195.136.125.34 25

ip nat inside source static tcp 192.168.10.35 25 195.136.125.35 25

after booting all is ok

there are 3 records in the arp-cashe:

Internet 195.136.125.33 - 0004.4d1f.3750 ARPA Ethernet1/0

Internet 195.136.125.34 - 0004.4d1f.3750 ARPA Ethernet1/0

Internet 195.136.125.35 - 0004.4d1f.3750 ARPA Ethernet1/0

but after some times first record in the arp table will lost for no reasons and I losing service via first IP address in static NAT

after router reboot all is ok again for some hours

Help please!! where is the problem?

4 REPLIES
VIP Purple

Re: losing arp record

Hello,

by default arp entries remain in the arp cache for 14400 seconds (4 hours).

You can increase the arp timeout with configuring the following in interface configuration mode:

arp timeout (0-2147483)

So the maximum timeout is 2147483 seconds, which is roughly 24 weeks. I am not sure but usually there is a setting whereby the arp entry does not timeout at all, it could be if you set the timeout to 0.

HTH,

Georg

New Member

Re: losing arp record

Hello Georg,

but why another two records not expired?

only firt...

VIP Purple

Re: losing arp record

Hello,

possibly the first NAT entry is not being used for an extended period of time (>4 hours) ? It could also be a software bug, which IOS version are you using ?

Regards,

Georg

New Member

Re: losing arp record

Hello,

using all entries for intensive mail traffic...

about 10 - 50 messages in a hour

IOS version is 12.2 (7b)

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