topic Re: Old IP addresses appear in arp table after changes in Operating System - HP-UX

Old IP addresses appear in arp table after changes

Attilio Gatto — Mon, 15 Jul 2002 12:41:51 GMT

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

Re: Old IP addresses appear in arp table after changes

Stefan Farrelly — Mon, 15 Jul 2002 12:44:01 GMT

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.

Re: Old IP addresses appear in arp table after changes

PIYUSH D. PATEL — Mon, 15 Jul 2002 12:48:06 GMT

Hi,

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

Piyush

Re: Old IP addresses appear in arp table after changes

PIYUSH D. PATEL — Mon, 15 Jul 2002 12:51:07 GMT

Hi,

# /usr/sbin/arp -s hostname hw_address

This will update the arp table.

Piyush

Re: Old IP addresses appear in arp table after changes

Peter Kloetgen — Mon, 15 Jul 2002 12:52:34 GMT

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

Re: Old IP addresses appear in arp table after changes

Attilio Gatto — Mon, 15 Jul 2002 13:45:42 GMT

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

Re: Old IP addresses appear in arp table after changes

PIYUSH D. PATEL — Mon, 15 Jul 2002 14:50:08 GMT

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

Re: Old IP addresses appear in arp table after changes

Attilio Gatto — Mon, 15 Jul 2002 15:10:35 GMT

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

Re: Old IP addresses appear in arp table after changes

Shannon Petry — Mon, 15 Jul 2002 16:12:11 GMT

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

Re: Old IP addresses appear in arp table after changes

rick jones — Tue, 16 Jul 2002 01:36:13 GMT

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.