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rkleemann

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rkleemann

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April 1st, 2006 00:00

Help with VLANs

Hi,

I'm trying to configure some VLANs on a powerconnect 2716.

Couple of questions:

1. Is the IP assigned to the switch tied to a particular vlan or port? It seems that if I create multiple vlans, I can only get to the switch if I'm using a port that's part of vlan1.

2. Is it possible for a port to belong to more than 1 vlan? The web management does not preclude me from configuring any port, to any vlan, including overlaps. In other words, I can go into "VLAN port settings" and assign port 5 to vlan2 and port 6 to vlan3. But if I go into "VLAN Membership" it's possible for me to select vlan2 and add port 6 to it. Which would mean that port 6 belongs to both vlan2 and vlan3. However, if I connect 2 hosts ifconfig'ed to be on the same network, on ports 5 and 6, they don't see each other. I'm guessing that's because originally the ports were set to different vlans, but what's the effect of adding the vlan3 port to vlan2, then?

So are vlans mutually exclusive on the ports, and if so, why does the web management allow me to add ports from other vlans?

Thanks
Ricardo
  • DELL-Cuong N.

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    Posted April 3rd, 2006 13:00

    First, I suggest reading some available resources online about VLAN technology to familiar yourself with the technology which will help you understand how to configure and manage your network (try google search - there are quite a number of good summary on VLAN available online).

    Now specifically to answer your questions:

    • 1 - The management VLAN is fixed to VLAN = 1 on this switch.  This means that you can only access the management IP address of the switch if you are communicating on VLAN 1.
    • 2 - A port may belong to more then one VLAN at the same time.  However each VLAN is completely independent of each others.  Also note that VLAN is a layer 2 feature not layer 3 feature which means that IP subnet information of the devices does not affect the VLAN behavior on a layer 2 switch.  So even if you have two devices with IP addresses on the same subnet and if they are on different VLANs then they still could not communicate to each others.  A layer 2 switch will NEVER forward packets from one VLAN to another.  If you need to forward packets across VLANs you need to do VLAN routing on a layer 3 switch.  The "port setting" for VLAN is to configure the "default" or "native" VLAN for a port (also known as PVID - permanent VLAN ID).  This PVID is used if a packet is received on a port without a VLAN tag already set on the packet.  If such a case occurs, then the switch will automatically assign this packet to the "default" VLAN ID of the port.  The port however will allow traffic from any other VLANs to which it is a member.  This means that if the packet enters the port with a VLAN tag then it will be compared to the port VLAN membership and if it matches then the packet is accepted otherwise it is dropped (if ingress filtering is enabled).  The port VLAN membership is also used to determine how the packet is forwarded within the switch.  After the packet is accepted the switch must determine where to forward the packet, and the packet will be forwarded only to other ports on the switch that are also member of the same VLAN ID to which the packet belongs.  I'm simplifying this a bit because packet forwarding also depends on MAC learning table per VLAN as well as other factorsk but I hope you get the general idea.

    I suggest reading up a little bit on how VLAN technology works, it will help you to understand better how to properly setup and manage your network in the long term.

    Cuong.

  • DELL-Cuong N.

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    Posted May 18th, 2006 15:00

    I'm not exactly sure what you are asking for but let me point you to the online user documentation that might help.  The manual for the 5324 can be found here: http://support.dell.com/support/edocs/network/pc5324/en/CLI/index.htm and here is the user guide: http://support.dell.com/support/edocs/network/pc5324/en/UG/index.htm

    First question - "What are the console commands to IP to 192.168.10.50?"

    I'm assuming you are trying to configure the management IP address for the switch?  If so please take a look at this section in the manual - http://support.dell.com/support/edocs/network/pc5324/en/CLI/ipaddres.htm#1050280

    Second question - "What are the console commands to VLAN ports 8,9,10,11 to vlan2?"

    Please look into this section of the manual - http://support.dell.com/support/edocs/network/pc5324/en/CLI/vlan.htm#1017913

    Note that you have to also decide on the correct mode for those ports (access, trunk or general) as well as whether they should accept untag traffic or not and what the PVID should be.  If you are not familiar with this concept, I suggest reading some of the whitepapers here: http://www.dell.com/content/topics/global.aspx/solutions/en/pwcnt_papers?c=us&cs=555&l=en&s=biz.  Also maybe do some google searches for additional information on VLANs.

    Cuong.

     

  • JoeNMI

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    Posted May 18th, 2006 15:00

    Hi Cuong,
         I am wanting to IP and VLAN a PowerConnect 5324 switch.
     
    What are the console commands to IP to 192.168.10.50?
     
    What are the console commands to VLAN ports 8,9,10,11 to vlan2
     
    Also what are the save configuration commands.
    Thanks in advance,
     
    JoeNMI