Primary and Secondary IP in VLAN

[SBraun]

Hi,

I hope this is the correct board, I think it could also be a routing-thread.

I have the following problem (with E5406):

I want two IP-Adresses in one VLAN, and the primary is then in the subnet of DHCP.

I entered IP 192.168.170.1 as primary

then I entered 128.170.30.1 as secondary

This is also what the documentation says

But when i then let me show the IP´s in this VLAN, it shows the 128.170.30.1 as primary

So the HP seems to ignore which IP you enter first, he takes the one with the lowest diggit as primary. This is a big fault!

Sure, in every documentation, the IP´s of the example-subnets are in ascending sequence, so this works. But if you do not so, it doesn´t work.

Is there a workaround to solve this problem?

Regards, Sven

[Vince-Whirlwind]

What is the practical difference between the IP address labelled "Primary" and the other one?

Do they both function OK as routers for their own subnet?

[SBraun]

The "Primary" is the new one where also the new DHCP is placed, the other subnet is the "old" subnet, but there is no more DHCP-Server placed.

The Problem is that the DHCP-requests will not be forwarded to the new DHCP in the "Primary".

The Routing in both subnets are working well.

[Vince-Whirlwind]

I may have misunderstood you, but if you have:

 - added a new subnet to an existing VLAN

 - moved DHCP services off the old subnet and onto the new subnet

 - you want devices on the old subnet to obtain an IP address from the new DHCP service

Then what you really need is to put an ip helper-address on the VLAN.

  vlan xxx ip helper-address <IP address of the new DHCP server>

[SBraun]

That´s all I did ;)

Maybe I should explain the steps. Before we had Components from Cisco, the we changed to HP and also changed in this step to new subnets. First we entered the new subnet-IP followed by IP-helper, then we added the old subnet-IP.

When we remove the "old" subnet-IP, all works fine. But when we add the "old" subnet-IP with 128.x.x.x the HP set this as "primary" and DHCP does not work anymore.

So it seems to be a real fault of HP because it sets the "primary"-subnet depending of the diggit, the lowest IP-subnet gets the status "primary", all others are "secondary". So the thing is that the statement of HP in the documentations, the first entered IP will get "primary", is simply wrong.

So I just want to know if there is a workaround or something to solve this problem. The workaround should not be deleting the 128.x.x.x-IP ;-)

With Cisco it is really easy, you enter the primary-IP, then you enter the secondary followed by "secondary" like this:

vlan 10

ip add 192.168.x.x 255.255.255.0

ip add 128.x.x.x 255.255.0.0 secondary

Regards, Sven

[Vince-Whirlwind]

I must say, I don't really understand the connection between DHCP and whether an IP address is configured on a VLAN as either Primary or Secondary.

(But then, this is a rare situation I've used very occasionally during a migration).

I'm thinking the Layer-2 broadcast should be seen by all devices in both subnets. If the DHCP server were confused about the source of the broadcast, I would expect you could get an IP address in the wrong subnet, but no IP address being issued at all is interesting...

Does an IP Helper help?

[SBraun]

An IP Helper does not help because of the wrong primary IP, the Switch forwards the request to the wrong subnet. It seems like the Switch does forward the DHCP request just to the primary subnet. And there, the IP Helper, which is the DHCP Server, can´t be found.

So for me is the question not really about DHCP, it is a problem caused of this, but I want to know why it works not like described, why is the first IP address you enter in a vlan not the primary IP if you enter after that an IP which is "lower".