Re: Just a reminder to not use Host Table Entries

Marc,

FYI: Skytap uses DHCP and works pretty well. That way they can change IP addressing from their portal, without touching your LPAR.


Diego E. Kesselman
diegokesselman@xxxxxxxxx

El 16 mar 2023, a las 8:40, Marc Rauzier <marc.rauzier@xxxxxxxxx> escribió:

Le 15/03/2023 à 13:23, Rob Berendt a écrit :

Marc,
I'm trying not to give a knee jerk reaction to ADDTCPIFC
INTNETADR(*IP4DHCP) DHCPDYNDNS(*YES).

Well, I was just interested to know if you did some work with IBM i as a dhcp client when you set your DR solution up. And if yes what were your findings, nothing more. I did not have enough time during my career to investigate that topic, although I was interested to do so. Therefore, I am curious about what people did with it.

1 - It's been a general belief here that servers should have fixed
addresses. Irregardless of platform.

Yep, but from time to time, one can try to improve all techniques (and, after following you on this list, I guess that you cannot argue that "if it works, don't change it"). There are pros and cons for fixed IP addresses for servers versus dhcp provided ones (example https://www.idkrtm.com/using-dhcp-is-better-than-static-ip-addresses-even-for-servers/). I just checked documentation and AIX and Linux both allow, like IBM i (since 6.1 or 7.1, most probably 7.1), using dhcp provided IP addresses. I am not saying that it is the best solution, but that it is one which may apply to some situations.

2 - How does this work when we deactivate that interface on our 10.10.6.x
network and activate it on our 10.27.6.x network?

Well, to be honest, I had this same question in mind when I asked you about dhcp investigation. I guess it is possible for dhcp to automatically update dns when it assigns or release an IP but, I do not know if it is possible when an interface becomes active or inactive. If you had investigated in this direction and found that it was working, I would have been happy to know it :-)

3 - When you have multiple interfaces (Domino, different websites,
backdoors for H/A software, etc) how does that play?

If they have all their own ethernet port this is not an issue, as the MAC address is, by default, used by IBM i to send to the dhcp server as an index of the device for IP assignment.
The dhcp RFC specifies that a request for a specific client id is possible if sent with the option 61 (checkout "9.14. Client-identifier" https://www.rfc-editor.org/rfc/rfc2132).
However, we come into an issue with IBM i, if you need more than two IP addresses per ethernet port. Because DHCPCLTID parameter of ADDTCPIFC command can indeed have only two values, *ADPTADR (which is the default and relates to the MAC address) and *DHCPUNQID (which is a system-wide unique identifier). As far as I know there is no way to enter any other value.
Note that AIX (checkout "option" in https://www.ibm.com/docs/en/aix/7.3?topic=files-dhcp-client-configuration-file) and Linux (checkout "option dhcp-client-identifier" in https://linux.die.net/man/5/dhcp-options) are able to specify any character string as client identifier, through the dhcp client options parameters. And therefore, for them, the limit to two IP addresses for an ethernet port does not exist.

On Sun, Mar 12, 2023 at 10:45 AM Marc Rauzier <marc.rauzier@xxxxxxxxx>
wrote:

Le 12/03/2023 à 15:17, Rob Berendt a écrit :

When we do a switch from our system at xx.10.xx.xx to our system at
xx.27.xx.xx we have API's on our IBM i automatically update that DNS to
change the entry.

Just curious: did you investigate using DNS dynamic update in
conjunction with setting up IBM i IP address as provided by a DHCP server?

ADDTCPIFC INTNETADR(*IP4DHCP) DHCPDYNDNS(*YES)

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