dell 1950 / dell powerconnect 6248 and VLANs

Vanush Paturyan misha at
Wed Jun 6 08:25:28 CDT 2007

On 6 Jun 2007, at 11:49, Arjen wrote:

> Hi,
> I am trying to configure vlans on my CentOS 4.5 box on a dell 1950.  
> I am
> able to create a vlan on eth1
> eth1 is up but no IP address
> eth1.2 is a vlan interface with address that has set a route
> for (shows up in the routing table)
> no iptables or other packet filtering mechanism for the moment
> interface connected to a Dell PowerConnect 6248 to a port that is in a
> configured VLAN on the switch consisting of four switchports. Two  
> hosts
> are connected to the same VLAN on the switch, having IP addresses
> and I have been trying tagged ports in the VLAN
> through the webinterface of the switch.

I am not familiar with Dell PowerConnect switch, but on a Cisco  
switches the interface on the switch should be configured as trunk  
(i.e. carry all VLANs over it, tagging packets appropriately.

> If I destroy the vlan on the Linux box and set directly  
> on the
> NIC and set the VLAN ports on the switch untagged I can reach both
> and If i try to route through the vlan as  
> described
> above I cannot. Tcpdump while pinging shows arp requests on the vlan
> interface.

What you're describing here suggests that interface on the switch is  
not going into trunk mode (sorry for uisng Cisco terminologi, I think  
it is called 802.1q trunk?)

Can you run tcpdump on eth1 (the one without IP address). I think you  
should see the same arp requests. Another thing you can do is to  
connect two machiens directly (nic to nic) with a crossover cable and  
run tcpdump on the other machine (this should capture packets as seen  
by the switch).

does that switch allow mirroring traffic from one interface to the  
other? If yes you can avoid using crossover cable and sniff the  
traffic this way.

Vanush "Misha" Paturyan
Techical Officer
Computer Science Dept.
NUI Maynooth

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