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Old IP addresses appear in arp table after changes

 
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Attilio Gatto
Occasional Contributor

Old IP addresses appear in arp table after changes

Hi,
I changed the addresses to our netport print servers on our HP-9000 HP-UX 11.0. I did an arp -a and the old addresses are still associated with the MAC address. How do I refresh the arp table in HP-UX 11.0 to recognize the IP addresses changes.

Attilio
9 REPLIES 9
Stefan Farrelly
Honored Contributor

Re: Old IP addresses appear in arp table after changes


Do an arp -d command to delete the old entry, then ping the new entry and the arp table will update with the new one.
Im from Palmerston North, New Zealand, but somehow ended up in London...
PIYUSH D. PATEL
Honored Contributor

Re: Old IP addresses appear in arp table after changes

Hi,

arp -d to delete the old entry. Once you ping the new ip address it will appear in the arp table.

Piyush
PIYUSH D. PATEL
Honored Contributor

Re: Old IP addresses appear in arp table after changes

Hi,

# /usr/sbin/arp -s hostname hw_address

This will update the arp table.

Piyush
Peter Kloetgen
Esteemed Contributor

Re: Old IP addresses appear in arp table after changes

Hi Attilio,

arp has a cache which remembers the information stored into it.( I think for 5 minutes) You first have to delete these informations using the command:

arp -d

After this the new IP- adresses will appear in arp cache, if you try to establish any connection to remote host.

Allways stay on the bright side of life!

Peter
I'm learning here as well as helping
Attilio Gatto
Occasional Contributor

Re: Old IP addresses appear in arp table after changes

Hi,

I did an arp -d {IP address}. I do an arp -a
the entry does not exist. I ping the hostname of the printer and the ping comes back with the old IP address. The /etc/hosts file is correct.

Attilio
PIYUSH D. PATEL
Honored Contributor

Re: Old IP addresses appear in arp table after changes

Hi,

What about changing the IP address on the printer server itself. Did you try with the arp -s command with the hostname and mac-address ???

Check the IP address if it exists in the /etc/rc.config.d/netconf file also

Piyush
Attilio Gatto
Occasional Contributor

Re: Old IP addresses appear in arp table after changes

Hi,
The IP addresses on the print servers are correct. If I do an arp -d the IP and MAC addreses are correct. When I ping the device using the alias I get the old IP address.

Attilio
Shannon Petry
Honored Contributor
Solution

Re: Old IP addresses appear in arp table after changes

If you manually delete the entry and it comes back with an old entry you are probably using arpd/rarpd.
The temporary fix is to add the arp entry manually with "arp -s hostname mac". Depending on your broadcast timer from arpd this may not last long.
Usually a router takes care of the arpd server and your workstation is a client.
You need to flush the arp table on your device pushing arp entries.

If it's a router and yours then the easy way is to power cycle it. If it's not yours then have the network admin take care of it.

Note: I have seen sites (and done so myself) where arp tables are manually loaded at system boot time. Hopefully this is not your case.

Regards,
Shannon
Microsoft. When do you want a virus today?
rick jones
Honored Contributor

Re: Old IP addresses appear in arp table after changes

it may sound like a silly question, but when you changed the IP address of the printer, did you happen to update all the sources of hostname to IP address translation? /etc/hosts, DNS etc? Does /etc/nsswitch.conf point to the sources of hostname to IP address translation that you updated?

That the ping of a hostname comes back with the old IP address implies that the hostname to IP mappings did not get updated.
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