2 computers sharing same IP address. 1st come, 1st served. 2nd come, what are my options?

Joe0x7F

Hello Everyone:

Regarding the Netgate 1100, 2100, AND 4200:

I would like to setup Static DHCP Mappings (with static ARP entries) as below.

DHCP Static Mappings
192.168.1.5 01:02:03:04:05:06 computerA
192.168.1.5 01:02:03:04:05:07 computerB

Q1.
I assume with this setup that the first computer that is booted up (and asks for an IP address from the DHCP server) will get IP address 192.168.1.5. Is this correct?

Q2.
And, the second computer that is booted up gets nothing/no IP Address.
Is this correct?

Q3.
What are my other options for getting the 2nd booted-up computer an IP address that is NOT 192.168.1.5? Is there a failover option? Will the 2nd computer get an IP address from the Primary Address Pool?

Thank you!

SteveITS

@Joe0x7F what OS? Windows has:

https://stackoverflow.com/questions/66171984/how-can-i-enable-tcp-ipv4-alternate-configuration-with-power-shell-on-win10

Joe0x7F

@SteveITS: Good one, Steve.

Sigh. But, computerA will probably be a Netgate 1100 and computerB will be an embedded device with an older Linux kernel on it, perhaps 2.6 or 4.4.

Thanks.

patient0

@Joe0x7F If I do that with two Debian clients the second one get's an IP from the DHCP range.

What DHCP server are you using, ISC DHCP or KEA?

Joe0x7F

@patient0: KEA

Joe0x7F

@patient0 said in 2 computers sharing same IP address. 1st come, 1st served. 2nd come, what are my options?:

@Joe0x7F If I do that with two Debian clients the second one get's an IP from the DHCP range.

Oh, Oh! That is excellent!

What DHCP server are you using, ISC DHCP or KEA?

KEA

Patch

@Joe0x7F said in 2 computers sharing same IP address. 1st come, 1st served. 2nd come, what are my options?:

I would like to setup Static DHCP Mappings (with static ARP entries)

Are you sure you want static ARP entries rather than just DHCP Mappings.
In my experience that causes cryptic failures. See https://forum.netgate.com/post/1216320

The alternative is just set the DHCP Mappings and let pfsense determine the ARP entries.

Joe0x7F

@Patch

Are you sure you want static ARP entries rather than just DHCP Mappings.
In my experience that causes cryptic failures.

No. I am not. Thanks for your experience! I will do what you suggest then.

Thanks!

Patch

@Joe0x7F said in 2 computers sharing same IP address. 1st come, 1st served. 2nd come, what are my options?:

will do what you suggest

Actually I'm no expert but stephenw10 is very clear in the above linked post.

patient0

@Joe0x7F oh, I just see you wrote about static ARP entries. Ignore my reply, I did static DHCP mapping.

Joe0x7F

Wow! Yall have been most helpful. Thanks!