Re: ONE Linux DHCP Server + Multiple VLANs - Soluble problem?

• From: Patrick O'Sullivan <patrick.osullivan@xxxxxxxxxxx>
• Date: Fri, 29 Jul 2005 22:37:13 -0400

There's an option in vconfig that might help you:

birdsong@phos:/usr/src/linux-2.6.11.11/net/8021q$ sudo vconfig --help

....

int vlan_dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct net_device_stats *stats = vlan_dev_get_stats(dev);
        struct vlan_ethhdr *veth = (struct vlan_ethhdr *)(skb->data);

        if (veth->h_vlan_proto != __constant_htons(ETH_P_8021Q)) {
                int orig_headroom = skb_headroom(skb);
                unsigned short veth_TCI;

                /* This is not a VLAN frame...but we can fix that! */
                VLAN_DEV_INFO(dev)->cnt_encap_on_xmit++;
....

I don't think you specified that flag so you might need to.

Hi everyone. I hope some of you could help with this headache problem
because I've really tried thousands of dhcp and interfaces configs
without success why does WinNT4 manage handle it and not the latest
linux kernel...

--- NETWORK SETUP ---

My company have 3 Cisco 3500XL switches and one Cisco Catalyst 4006
router.

Every switch act as a VTP Client to the Catalyst which acts as a VTP
Server. My current configuration uses the old Windows NT4 as DHCP and
DNS server and a linux box as a file server.

I have configured 4 VLANs (100, 200, 300, 400), and my Windows NT4 box
assigns DHCP adresses to the current VLANs with the rigth VLAN IP.
Everything works fine. The servers are in VLAN 100 and the other office
computers are in the others.

Now, I setup a linux box (Debian 3.1 stable, customized 2.6.12 kernel
with 802.1q as a module and VLAN support as static)

I compiled vconfig tool from the kernel sources, I checked if the
driver of my 2 NIC cards (3c509c) is correctly patched to handle VLAN
Trunk. It's ok.

I can add with vconfig new vlan interfaces on my linux box, it works
without freezing the entire box. Until now, no problem.

The DNS server is up and running, I can switch off the windows box and
the linux box can take the job. But...

--- THE REAL TROUBLE ---

I tried to configure the DHCP Server (apt-get install dhcp3-server) to
handle the VLANs. And nothing works from now on...

Here are the steps I think it's supposed to work (I disabled the second
NIC, it will be used in the future to do load balancing with bond0, so
only eth0 is concerned for my test):

0. The linux server adress is 10.50.100.10 with default gateway
10.50.100.1 and the Catalyst holds an ip-helper-adress for dhcp to the
linux box.

1. Add 3 virtual network interfaces with vconfig, so

  vconfig add eth0 200
  vconfig add eth0 300
  vconfig add eth0 400

2. Set up IP for the new interfaces

  ifconfig eth0.200 10.50.200.5/24 broadcast 10.50.200.255 up
  ifconfig eth0.300 10.50.300.5/24 broadcast 10.50.300.255 up
  ifconfig eth0.400 10.50.400.5/24 broadcast 10.50.400.255 up

3. DHCP Configuration

subnet 10.50.200.0 netmask 255.255.255.0 {
        authoritative; # I TRIED WITH OR WITHOUT IT
        option routers 10.50.200.1;
        range 10.50.200.10 10.50.200.160;

}

subnet 10.50.300.0 netmask 255.255.255.0 {
        authoritative; # I TRIED WITH OR WITHOUT IT
        option routers 10.50.300.1;
        range 10.50.300.10 10.50.300.160;

}

subnet 10.50.400.0 netmask 255.255.255.0 {
        authoritative; # I TRIED WITH OR WITHOUT IT
        option routers 10.50.400.1;
        range 10.50.400.10 10.50.400.160;

}

That should be enough for the config. I read many notes on internet, I
even tried to put the whole in a shared network or in separate
declaration. Nothing works!

I launched the dhcp server in debug mode to see the details for the
connections. And the problem is that...it isn't even asked to offer an
IP.

--- THE ANALYSIS ---

So I tried to sniff packets with tethereal to see what was going on.
And when I launch it with:
  tethereal -V -f "vlan or (port bootpc or port bootps)"

  Notings happens (I configured the switches to add VLAN Trunks).

And by chance, I did try to add virtual interfaces with

  ifconfig eth0:1 10.50.200.6/48 broadcast 10.50.255.255 up

  -> Notice the /48 and the broadcast!

And I tried once again dhcp in debug mode and sniffing packets...and
here is the result when I restard the connection on two Windows 2000
clients:

  Multiple interfaces match the same subnet: eth0 eth0.100
  Multiple interfaces match the same shared network: eth0 eth0.100
  Listening on LPF/eth0.100/00:50:da:66:67:2d/10.50.100.0/24
  Sending on   LPF/eth0.100/00:50:da:66:67:2d/10.50.100.0/24
  Listening on LPF/eth0.200/00:50:da:66:67:2d/10.50.200.0/24
  Sending on   LPF/eth0.200/00:50:da:66:67:2d/10.50.200.0/24
  Listening on LPF/eth0/00:50:da:66:67:2d/10.50.100.0/24
  Sending on   LPF/eth0/00:50:da:66:67:2d/10.50.100.0/24
  Sending on   Socket/fallback/fallback-net

  DHCPDISCOVER from 00:12:79:68:0c:0e via 10.50.200.2
  DHCPOFFER on 10.50.200.160 to 00:12:79:68:0c:0e (w2k) via 10.50.200.2

  DHCPDISCOVER from 00:12:79:68:0a:b5 via 10.50.100.2
  DHCPOFFER on 10.50.100.160 to 00:12:79:68:0a:b5 (PST2) via
10.50.100.2

  DHCPDISCOVER from 00:12:79:68:0c:0e via 10.50.200.2
  DHCPOFFER on 10.50.200.160 to 00:12:79:68:0c:0e (w2k) via 10.50.200.3

  DHCPDISCOVER from 00:12:79:68:0c:0e via 10.50.200.2
  DHCPOFFER on 10.50.200.160 to 00:12:79:68:0c:0e (w2k) via 10.50.200.2

  DHCPDISCOVER from 00:12:79:68:0a:b5 via 10.50.100.2
  DHCPOFFER on 10.50.100.160 to 00:12:79:68:0a:b5 (PST2) via
10.50.100.2

  DHCPDISCOVER from 00:12:79:68:0a:b5 via 10.50.100.3
  DHCPOFFER on 10.50.100.160 to 00:12:79:68:0a:b5 (PST2) via
10.50.100.3

  .
  .
  .

And the tethereal sniffs packets with the correct VLAN ID in it...

But the clients never get their IP. So if anyone could answer why. And
why does dhcp offer IP when adding the strange interface eth0:1, and by
chance I remind you of it.

Any help is greatly welcome.

Regards,

Adrian

--

Patrick O'Sullivan
Rutgers University Network Operations
patrick.osullivan@xxxxxxxxxxx
.

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