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Trunk mode on a port of a Cisco 2970

Fofolito -  
 ciscowarrior -
Hi,

I'm using a Cisco 2970. I wanted to know if by configuring a port in trunk mode (and others in access mode), and connecting a computer to the port in trunk mode, I could access machines on any port that belong to any VLAN.
If not, why??

Thanks in advance... @+
Configuration: Cisco 2970 Switch Windows XP Pro

10 answers

  1. perceus
     
    Hello,
    a trunk is a multi-VLAN link that serves to connect multiple identical remote VLANs through switches
    so the ports that you have set to trunk mode will only be used for that router---switch or switch--switch
    if you want to be able to communicate with all the machines in all your VLANs, you'll need to connect a router in trunk mode as well, configure as many sub-interfaces as you have VLANs, and create routes to these different VLAN subnets
    and of course, put your machine in one of these VLANs
    3
  2. Fofolito Posted messages 38 Registration date   Status Member 8
     
    Hello,

    Well, I think we can't connect the computer to a port in trunk mode, because a computer can't belong to multiple VLANs at the same time. So, trunk links are only used between switches or between a switch and a router.
    But I'm not too sure, so if I could get a confirmation, I would be very grateful.
    Thanks in advance...
    3
    1. brupala Posted messages 111140 Registration date   Status Member Last intervention   14 441
       
      It's nearly that, yes.
      With the exception that certain servers (in fact, some network card drivers) can manage VLANs, just like some routers.
      --
      And... There you go!
      0
  3. brupala Posted messages 111140 Registration date   Status Member Last intervention   14 441
     
    The 802.1q (and 802.1p) protocol adds 4 bytes to carry the VLAN number in the Ethernet header of the frame.
    If the network interface doesn't know how to read these 4 bytes and acts as if they don't exist, the rest of the data in the frame is not understood and the frame is discarded.
    See:
    http://www.cisco.com/en/US/tech/tk389/tk390/technologies_tech_note09186a008009466...
    Moral:
    You need a network card with a driver capable of reading 802.1Q tags; otherwise, splash.
    And also a network card capable of receiving frames larger than the standard maximum size (1522 bytes instead of 1518).
    --
    And ... Here you go!
    3
    1. Mel
       
      Hello,

      Do you know if there is a tool to capture Ethernet frames with the IEEE 802.1P field?

      Does the router automatically remove this field on a port configured in access mode?

      With Ethereal, I can't capture this field, and I don't know if it's removed by the router or by the PC.

      Thank you in advance!
      0
    2. brupala Posted messages 111140 Registration date   Status Member Last intervention   14 441 > Mel
       
      router or switch?
      on an access port, for sure, the field is removed.
      otherwise,
      when it is present, on my end, it is very well recognized and decoded by ethereal or wireshark.
      The PC (or rather the ethernet driver) cannot remove this field, at least on reception: to remove it, you have to know it exists, so if you know it exists, it means you are managing it.
      -- 
      and ... Voili Voilou Voila !
      0
    3. Catalyst2960
       
      Is it possible for the network card of my server (DHCP under Windows 2003) to support the additional 4 bits in the frames called the tag, and to use this Tag to decide the 'scope' of the IP address that will be assigned to the client that sent the DHCP request?
      For example: The tag indicates that the request comes from VLAN 2, so assign an IP address from a specific scope.

      If yes, how do we configure this choice of scope based on the VLAN from which the DHCP request originates?

      PS: WITHOUT the ip helper command (the 2960 switch only does layer 2 and I only have 2 fa interfaces on my router: internet and my LAN network to my switch)
      0
    4. brupala Posted messages 111140 Registration date   Status Member Last intervention   14 441
       
      Hi,
      your question would have deserved a new discussion, it doesn't have much to do with the original topic.
      But, if your server has multiple connected VLANs, it has as many IP networks and the ranges are chosen based on the IP address of the interface that receives the DHCP request (the DHCP discover).
      0
    5. Catalyst2960
       
      The first question is the one that was closest to my dilemma, sorry.

      But the problem is that I have only one interface on my router that I can plug into my switch, my VLANs do not have an IP address, my goal would be to connect a single cable from my server to my switch and have that port access all my VLANs to distribute an IP address to them. So there is no source address for my DHCP server to know which scope to assign. That's where I wanted to configure a trunk from my switch to the network card of my DHCP server so that it can redistribute the IP addresses according to the VLAN with the "tag".
      I am limited in the configurations of my switch; it only operates at layer 2.

      Do you have a solution? Thanks ^^
      0
  4. sasuke
     

    Hi, thanks for your response, but if I'm not being too demanding, I would like a definition of what trunk mode means and how to use it. Also, the design I need to create consists of a router, a switch, and 3 VLANs. And please, one last thing, I would like the user manual for Packet Tracer. Thank you very much!
    1
    1. brupala Posted messages 111140 Registration date   Status Member Last intervention   14 441
       
      Well,
      if you want to ask how to make this model with 802.1q VLANs, you'll need to specify in a new discussion what exactly you want to do and with which equipment because we're not very good at guessing.
      --
      And ... There you go!
      0
  6. kurtil Posted messages 10 Status Member 1
     
    If it's at the packet tracert level that you're talking about, then you must use Cisco:
    To declare a trunk at the port level with 802.1Q encapsulation, do it like this:
    enter privileged mode: command: "enable"
    Type the password
    Enter the run config command: "configure terminal"
    go to the desired interface, for example fastethernet 0/24 command: "interface fa0/24"
    Set the encapsulation 802.1Q: "switchport trunk encapsulation dot1Q"
    then set the port to trunk mode: "switchport mode trunk"
    It should be noted that on some Cisco switches it is not necessary to specify the encapsulation type (on the 2950 for example, but it is necessary on the 2960, so I suppose that on the 2970 it is necessary to declare the encapsulation type).
    There you go
    1
  7. sasuke
     
    Thank you, I finally got what I wanted, but it remains theoretical. I'm still having problems with the simulator, and I don't know how to explain my issue, but I will try:

    You know, when we start Packet Tracer, for example, we choose a router + a switch + two PCs. Normally, and as far as I know, the switch will be connected to the router, and the two PCs will be connected to the switch. My first problem is that I don't know what type of cabling to choose. It’s true that the main rule is: between two different machines we use a straight cable, and between two machines of the same type we use a crossover cable, but how to differentiate between these two cables among all the cables that exist in Packet Tracer? Then, when we finish the connections, we click on the router, for example, to configure it, and the same for the switch; I don't know how to do that. I swear it pains me not to know how to do it, but it's a bit hard, and I'm sorry, this will be my last question.
    1
  8. sasuke
     

    Could you please provide me with a course on trunk mode or where I can find its user manual, how to configure it? Thank you in advance.

    0
    1. brupala Posted messages 111140 Registration date   Status Member Last intervention   14 441
       
      The trunk mode can refer to two different things depending on the manufacturers, these two things can converge and work together.
      Either the transport of VLAN information between the switches: 802.1q
      Or using multiple lines in parallel between two switches but managing them as one: 802.3ad
      It's up to you to specify what you want to do.
      --
      And ... There you go!
      0
  9. kurtil Posted messages 10 Status Member 1
     
    The trunk mode allows the transmission of different VLANs declared within the switch. It is primarily used for inter-switch links. For example, VLANs are declared in the "VTP database" of a level 3 switch in server mode, and all additional switches are declared in client mode. When interconnecting the switches with the level 3 switch, you set the ports to "trunk" with an encapsulation of 802.1Q. This allows you to retrieve all VLANs on the other switches without needing to declare them one by one.
    Basically, trunk port = a port that carries all VLANs or specified ones
    and access port = a port tagged in a specific or native VLAN.
    I hope I’ve clarified your ideas.
    0
  10. sasuke
     
    Hello again;

    "You declare the ports in 'trunk' with 802.1Q encapsulation." How do you declare them, and if it's at the level of a simulator, how do you do it?

    I don't think you have a course; I think it would be simpler because I'm afraid of being a bother.

    Thank you immensely.
    0
    1. brupala Posted messages 111140 Registration date   Status Member Last intervention   14 441
       
      yes:
      http://www.cisco.com/univercd/home/home.htm
      --
      and ... There you go!
      0
  11. ciscowarrior Posted messages 810 Status Member 100
     
    Hi,

    NO.

    If you want to communicate between VLANs, you need to do routing, and since the 2970 is an L2 switch, you have to go through a router configured in Router On A Stick, or connect as many router interfaces as you have VLANs.
    Then from any machine, you will be able to access all the machines.
    Do you have a Cisco router available?

    Alain
    0