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Wired Networks Thread, DHCP & VLAN problems in Technical; Hi there, I'm trying to set up a guest network and am running into problems with the VLANs - I ...
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    DHCP & VLAN problems

    Hi there,
    I'm trying to set up a guest network and am running into problems with the VLANs - I assume.
    I have a Unifi UAP with 2 SSIDs (call them internal and Guest).
    I have a BT Home Hub v3 serving DHCP on a 192.168.19.*/24 scope - this is the internet network and only generally has 2 leases.
    I have a windows server 2012 box serving IPs on 192.168.18.*/24 - this is the internal network used for most things.
    I have a web filter that routes between .19.* & .18.* perfectly - essentially a second router.

    I have a GS724T switch with 2 vlans set up
    VLAN1 in the main, default vlan that is on the 18.* network. All ports apart from 1&2 are assigned to this VLAN.
    VLAN2 is the internet vlan and has port 1 (home hub), port 2 (web filter) and port 3 (Unifi AP) I have set the guest network to VLAN2 - but no DHCP gets picked up by the client. I want the guest network to have a 19.* IP - which means no filtering - I have my reasons.

    In essence, It appears that DHCP requests aren't being forwarded to the home hub, or the responses aren't being relayed back.

    Does anyone have any ideas? This is currently a home project, but it's because we're wanting to do something similar at work.

    Many thanks, don't hesitate to ask for any more info.

    Bryn
    Last edited by bmoorhouseSTM; 1st August 2013 at 11:04 PM.

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    ass17's Avatar
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    Each vlan interface has to have some sort of dhcp helper or address setup.

    On HP switches you set the dhcp IP helper command.

    With netgears should should be able to kill several birds with one statement:

    bootpdhcprelay serverip {ip address of dhcp server}
    Example:
    bootpdhcprelay serverip 192.168.18.1

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    ass17's Avatar
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    This image shows you in more detail:
    Code:
    https://c919f6a6-a-e4ee3bb8-s-sites.googlegroups.com/a/kossboss.com/main/vlans/dhcp3.png
    The image doesn't work in the edugeek app on iOS, think its s issue with PNG files so view it on a pc/mac.
    Last edited by ass17; 1st August 2013 at 11:48 PM.

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    twin--turbo's Avatar
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    Quote Originally Posted by ass17 View Post
    Each vlan interface has to have some sort of dhcp helper or address setup.
    As all ports 1-3 are on the same vlan then there is no need for a DHCP helper between the client and the dhcp server on the switch.


    Tests to do,

    Plug in a PC insted of the UNIFI and see if that gets an IP, if not then set a static .19. IP on the laptop and confirm you can ping the home hub. If you can't ping the home hub then you need to check the switch setup.

    If you do get the DHCP with a PC plugged in and not with the WIFI then chech on the UNIFI for DHCP relay settings that may need to be altered.

    TT

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    With netgears should should be able to kill several birds with one statement:

    bootpdhcprelay serverip {ip address of dhcp server}
    Example:
    bootpdhcprelay serverip 192.168.18.1
    Unfortunately this won't work on my switch at home, but MAY work at work. The GS724t that I own doesn't appear to have telnet access so I can't run those commands. The switches at work have telnet, but I won't be permitted to change the settings unless I have a damn good reason, which, at the moment I don't.

    Plug in a PC insted of the UNIFI and see if that gets an IP, if not then set a static .19. IP on the laptop and confirm you can ping the home hub. If you can't ping the home hub then you need to check the switch setup.
    If I plug a device into port 3 of the switch (where the UNIFI is plugged in) then it will get an IP on the 18.* subnet as port 3 has both vlan1 and vlan2 assigned to it. The guest SSID on the unifi is set to vlan2 which SHOULD give it a .19.* IP but I don't get one. The internal SSID does not have a VLAN option set and picks up the correct IPs (.18.*).
    I've just verified that DHCP works through the VLAN by putting a port (4) into JUST vlan2 and connecting a laptop. Worked flawlessly and picked up a 19.* IP which leads me to think that the VLANing on the switch is different to the VLANing that the unifi is doing. How, I'm not sure...

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    That settles it, it is VLANing differently. I've just set a static IP, connected to the guest network and I can't ping the home hub... I've had a think, and I think it must be the switch.
    Theory 1: The VLANing on the switch isn't attaching VLAN tags, it's just effectively stopping the ports from seeing each other. The Unifi on the other hand is attaching VLAN tags which the switch can't interpret and therefore nothing is getting done with the packet.
    Theory 2: The VLANing is attaching tags at both the unifi and the switch but the Homehub can't interpret the packet, so it's being discarded.

    That said, the switch shows no TX or RX errors for any ports so it's not just reading it as a faulty packet which is interesting. I'm really stumped by this one.

    Oh, many thanks for the help I've had so far, and I'm sure I'll get in the near future - it's very much appreciated.

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    ass17's Avatar
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    Just quick question, is the AP on port 3 tagged or untagged?

    Our ruckus APs sit on a main untagged VLAN and all the SSIDs sit on different tagged VLANs. With netgear make sure the ports PVID is set to the same vlan you wish the untagged traffic of the AP to go down.

    This article describes the process as you require:
    http://wiki.ubnt.com/UniFi_and_switc..._configuration

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    twin--turbo's Avatar
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    According to the user manual the GS724 supports 802.1Q Vlan Trunks, make sure the port is set as a trunk.

    The AP should support 802.1Q too.

    Rob

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    Hi folks, I totally forgot to come back here and reply. Sorry. If anyone is interested, the switch was on port based vlan, not 802.1Q. I changed that and away I went. Thanks for everyone's help, and sorry!

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    twin--turbo's Avatar
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    Always interested to hear when something is fixed

    TT

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