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1224ST Having issues with DHCP

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Thanks to we have the system up and functioning as it should...mostly : )

We have all our ports configured as 'switchport mode trunk' and 3 vlan's (1 Default, 2 voice_network, 3 user_network).  We have no ip helper address setup.

We have a total of 3 switches in different locations and here is how our system is laid out

DHCP server -> switch1 -> switch2 -> switch 3

On the windows machines, we're able to get an IP address from DHCP, but on our phones and our Mac computers, we have to statically assign an IP address or it'll never get one.  I looked into UDP Relay options, but that's not available in the web interface on the 1224ST's.  Is there something obvious I'm missing?

On a side note, in the web interface, switch 1 and 2 have Enable DNS Lookup checked but do not have anything written in the Primary or Secondary IP address.  Should I uncheck this?

Thanks again!

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Anonymous
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Re: 1224ST Having issues with DHCP

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:

If it takes that long to get an IP address via DHCP, often the cause is multiple DHCP servers on the network.  Is it possible there is another device offering DHCP addresses on the network?

Levi

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Anonymous
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Re: 1224ST Having issues with DHCP

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:

Thank you for asking this question in the support community.  I will be happy to help you troubleshoot this, but it may be beneficial to obtain some more information.

  • What VLAN is the DHCP server on?
  • What subnetworks is the DHCP server configured to offer addresses for?
  • What VLAN are the windows machines on that are receiving an IP address via DHCP?
  • What VLAN are the phones and Mac computers on that are not receiving an IP address via DHCP?

Typically, you do not need any DNS settings on the 1224 series switches, and it sounds like this is the case in your network.  The global DNS settings for these switches is so the unit can contact a DNS server if it needed to.  This would be the case if you typed ping <domain name> from the unit.  These settings should have no affect on the devices connected to it.

Levi

Levi

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New Contributor

Re: 1224ST Having issues with DHCP

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The DHCP server isn't set for a particular VLAN (network card doesn't support VLAN tagging). But I might not understand the question.  It is plugged into port 1 that's configured 'switchport mode trunk'.  I would guess it's default is VLAN 1.

10.122.143.x <- for computers

10.10.1.x <-for phones

None of our computers are set to be on a specific VLAN.  Maybe this is where the problem is.  I thought all the ports should be 'trunk' to allow any VLAN through without tagging it?  The phones are default configured to VLAN 0 (ShoreTel IP phones).

Thanks,

Ramin

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Anonymous
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Re: 1224ST Having issues with DHCP

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:

Based on my understanding of the network design, you will want the phones to boot in the native VLAN (1 in most cases by default) of the network (not VLAN 0).  Then they will request an address via DHCP on the native VLAN.  In your case, the phones will most likely request a DHCP address with options.  The DHCP server will receive this DHCP DISCOVER message with options, and then tell the phones to reboot into the desired VLAN.  Then the phones will reboot in the desired VLAN, and request an address for the subnetwork assigned to that VLAN on the DHCP server.  Keep in mind that this configuration will need to be done on the DHCP server.  It will have to know to instruct the phones to reboot into a new VLAN based on the DHCP options it received in the DHCP DISCOVER message.  Also, when the phone reboots and the DHCP server receives the new DHCP DISCOVER from the phone on the new VLAN, it will have to know that it received this on a non-native VLAN and assign it an address based on that VLAN.

Furthermore, if the PCs are connected to the phones, and then the phones connect to the switch, the switchports on the switch should be configured as trunks, which will allow multiple VLANs (both phones and PCs) to traverse the link.  The DHCP server will need to assign PCs addresses in the native VLAN.

With this design, the PC should obtain an IP address from the DHCP server, and the phone should receive an IP address from the DHCP server, which then instructs it to reboot into a new VLAN.

If you would like to reply and attach a copy of your current ADTRAN configuration, I will be happy to review it for you.

Levi

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New Contributor

Re: 1224ST Having issues with DHCP

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That is correct.  Here's a copy of 1 of our configs.  The only difference is the vlan 1 management IP address...the rest of the configs are the same.

Thanks!

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Anonymous
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Re: 1224ST Having issues with DHCP

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:

Thank you for attaching a copy of your configuration.  In this configuration,  it is as I explained previously.  Everything that is not tagged before it arrives at the switch will be associated with the native VLAN 1.  Therefore, since PCs do not typically tag traffic with VLANs, they will be untagged when they arrive at the switch and be sent to the DHCP server untagged in the native VLAN 1.  The phones will need to be configured as mentioned above.

Let me know what additional questions you have.

Levi

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New Contributor

Re: 1224ST Having issues with DHCP

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Well, I guess if there's nothing wrong with the configuration of the switch, I'll have to check and see where the problem with the network is otherwise.  We're still having problems getting a DHCP on our machines.  It takes nearly 2 minutes to get one!

Thanks

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Anonymous
Not applicable

Re: 1224ST Having issues with DHCP

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:

If it takes that long to get an IP address via DHCP, often the cause is multiple DHCP servers on the network.  Is it possible there is another device offering DHCP addresses on the network?

Levi

View solution in original post

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Valued Contributor
Valued Contributor

Re: 1224ST Having issues with DHCP

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Microsoft has a great tool to check for Rogue DHCP servers:

Rogue DHCP Server detection - Microsoft Windows DHCP Team Blog - Site Home - TechNet Blogs

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New Contributor

Re: 1224ST Having issues with DHCP

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Found the issue, DHCP Relay was set on our Watchguard router....

Fixed the DHCP issues!

Thanks!