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DHCP relay on PC22604 switches

Discussion in 'Networking Issues' started by cameramonkey, Apr 21, 2005.

  1. cameramonkey

    cameramonkey Network Guru Member

    Well, after being bounced around no less than 3 hours in two days (no exaggeration) in the queues at linksys doing nothing but describing my symptoms with not even an ATTEMPT to fix my problem (its over my head sir, let me escalate it), I thought I would give this a shot.

    We are trying to segment out a network using a PC22604 switch. The overall config is below.


    Vlan1 IP
    Vlan1 on tagged ports 1 3 4 5 6 7 8
    Pvid set to 0x001 on above ports

    Dhcp server
    Scope1 192.168.100.x
    Scope2 172.17.0.x

    Vlan2 on tagged port 2
    Pvid set to 0x002 on port 2

    DHCP Forwarding enabled on vlan2
    vlan1 as outbound relay IP.
    Preferred server (tested with this, as well as all preferred server fields blank.

    Data routed between vlans test OK

    Problem description:

    If PC is setup on vlan 2 with static address of data is routed ok across both vlans, and out to the internet.

    If PC is setup on vlan1 with DHCP enabled, it is assigned an IP from scope 1
    If PC is setup on vlan2 with DHCP enabled, it never gets an IP.

    I have heard some rumblings that layer 2 switches cant normally forward dhcp requests. If that is true, what is the "DHCP Forwarding" config on this switch used for? I have done this before across VPNs using wifi devices that do relaying without a problem, so I know my DHCP scopes are setup right.


  2. cameramonkey

    cameramonkey Network Guru Member


    Well, after doing some very basic sniffing on vlan1, we are seeing the dhcp broadcast packets that are originating from the vlan2 segment. However, its showing up as coming from the mac address of the switch. I get the feeling that my DHCP server just cant quite figure out the source subnet so it can assign the right address.

    Any ideas what setting I am missing? could it be a vlan tagging issue? arp proxy issues?

    I did get it setup and working for a breif moment. I got the laptop to get a dhcp address once, but apparently it was in the middle of tweaking and I have no clue what I changed. So close, yet so far.

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