All these things are true (good list) and there is more:

Entries in DNS have TTL value. TTL is Time to Live outside of the DNS.
Suppose the TTL is set at 24 hours (not an unreasonable number). A PC in
your network requests the address of the system rom DNS and is given the
current IP address as well as this 24 hour cache value. That PC will not
ask for an address translation again for 24 hours. So if you change the
DNS only one hour after this PC has requested the address then that PC
won't know about the change for 23 more hours. There are three ways to
work around this problem:

1) After changing the DNS, reboot every device in your infrastructure so
that they all dump their DNS caches and request the new address. (Hey I
didn't say all the workarounds were good ones!) A slight variation on
this is to run IPCONFIG /flushdns on every windows machine which
accomplishes the same thing.

2) Several days before the change in address, change the TTL in the DNS to
5 minutes. This will cause extra DNS traffic for that time but when the
change is made it will only be 5 mintues for everything in the network to
get the new address. Once the change is complete re-up the TTL to the
previous value.

3) Leave both IP addresses alive on the system for at least the time the
address lives in DNS. This has the additional benefit of being able to
use NETSTAT and/or iNav to see if there are any remaining connections to
the old IP address. Until there are NONE that old IP is still in use.
Once it remains clear for a few days THEN you can take it down without Mr
Franz 'Ooops' :-)

- Larry

Larry Bolhuis IBM Certified Advanced Technical Expert -
System i Solutions

The AS400 will not care but some applications might. You have to look at
the applications that are running on & talking to the system. In the past
I have worked with IBI WebFocus; it stopped working once we changed the IP
address. I have also seen Cognos apps that had the IP address embedded. If
you use Vision Solutions HA software then it may have the IP address coded
instead in the IP address in the configuration. If you use iTera HA then
you will have the IP address hardcoded. If you have users that have put an
entry into the hosts table on their PCs then they may have a problem


Sent: Wednesday, July 2, 2008 4:43:17 PM
Subject: ip address

If we change the ip address of the AS/400 and keep the host name same,
will there be any impact if we use only host name?

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