About VLAN

MatroMatro Member Posts: 38 ■■□□□□□□□□
I've a question about VLANs....

When hosts transmit frames inside the vlan, are these tagged (by 802.1q protocol) or not?

I think that tag are only used in trunks, for recognize the different destination VLAN; frames are untagged when flows on the access port of the vlan.
If this vere true (frames inside a VLAN are untagged), connecting two VLAN together with a crossover cable (on access ports, not by a trunk) should connect two different hosts and be able to ping each other, if they are in the same subnet.

HOST A (192.168.1.1/24, VLAN 1) -->cross cable--> HOST B (192.168.1.2/24, VLAN 2)

I did this test, but it doesn't work.


What's wrong?

Thanks guys ;)
Actually: CCNA - Palo Alto ACE

Comments

  • MatroMatro Member Posts: 38 ■■□□□□□□□□
    https://learningnetwork.cisco.com/thread/21665

    As I thought, in this thread they confirm that on a trunk port frames are tagged, otherwise on access port are untagged.. Why my test did not work? icon_sad.gif
    Actually: CCNA - Palo Alto ACE
  • xnxxnx Do they matter? UKMember Posts: 464 ■■■□□□□□□□
    Get Wireshark and check out the frames...?
    Getting There ...

    Lab Equipment: Using Cisco CSRs and 4 Switches currently
  • Adam BAdam B Member Posts: 108 ■■□□□□□□□□
    Regardless of the fact that they're in the same subnet, theyre in a different vlan, which means trunking is necessary. Also, do you have a router connected? You will need one unless youre doing layer 3 switching, in which case, the pings will not work. Correct me if I'm wrong and if you have any questions just reply. I'm currently studying for my CCENT still so any question I can answer to the best of my knowledge will hopefully reinforce it. "Routers in VLAN topologies provide broadcast filtering, security, address summarization, and traffic flow management. None of the switches within the defined group will bridge any frames, not even broadcast frames, between two VLANs. Several key issues described in the following sections need to be considered when designing and building switched LAN internetworks: "<--- Reason why Routers are needed in VLAN topologies, if you are using Layer 2 Switches.
    2015 Goals: CCNP SWITCH [] SEC+ [ ] CCNP ROUTE [ ] CCNP TSHOOT [ ]

  • RouteMyPacketRouteMyPacket Member Posts: 1,104
    You have made it more complicated than it is, why use 192.168.1.1/24 for VLAN 1 and 192.168.1.2/24 for VLAN 2? These IP's belong to the same network so why would you ever use another VLAN? You wouldn't...ok so do this

    VLAN 1 - 192.168.1.0/24
    VLAN 2 - 192.168.2.0/24

    Ok, now how can a client on VLAN 1 communicate with a client on VLAN 2? What is needed to allow this communication to take place? You could make it even easier and use one L3 switch for this test but again, what do we need for this to take place?
    Modularity and Design Simplicity:

    Think of the 2:00 a.m. test—if you were awakened in the
    middle of the night because of a network problem and had to figure out the
    traffic flows in your network while you were half asleep, could you do it?
  • d4nz1gd4nz1g Member Posts: 464
    That's because you created a broadcast limitation, that way arp broadcasts won't be heard from vlan 1 on vlan 2
  • Adam BAdam B Member Posts: 108 ■■□□□□□□□□
    You have made it more complicated than it is, why use 192.168.1.1/24 for VLAN 1 and 192.168.1.2/24 for VLAN 2? These IP's belong to the same network so why would you ever use another VLAN? You wouldn't...ok so do this

    VLAN 1 - 192.168.1.0/24
    VLAN 2 - 192.168.2.0/24

    Ok, now how can a client on VLAN 1 communicate with a client on VLAN 2? What is needed to allow this communication to take place? You could make it even easier and use one L3 switch for this test but again, what do we need for this to take place?
    Good Point about the IP addresses, didnt catch that.
    2015 Goals: CCNP SWITCH [] SEC+ [ ] CCNP ROUTE [ ] CCNP TSHOOT [ ]

  • MatroMatro Member Posts: 38 ■■□□□□□□□□
    It's not an error, i know that i should use different subnet on different VLAN.
    It's only for learning reason, i want to understand why frame that go out from and go into ACCESS ports, so untagged frame, can't reach another VLAN!
    I will never use this configutation, it's only to better understand how it works :)
    Actually: CCNA - Palo Alto ACE
  • MatroMatro Member Posts: 38 ■■□□□□□□□□
    It works!!! :D Now I'm happy.

    I made a mistake, I thought switch ports were in access mode, but all were dynamic desiderable. So, connecting the two dynamic desiderable ports made a trunk connection. Clearly hosts can't ping, due to the tag.
    Modified ports to access mode... ping ok 100%!

    Sorry for the stupid scenario, but i like to understand well what bits do inside the cables icon_study.gif
    Actually: CCNA - Palo Alto ACE
  • no!all!no!all! Member Posts: 245 ■■■□□□□□□□
    You have made it more complicated than it is, why use 192.168.1.1/24 for VLAN 1 and 192.168.1.2/24 for VLAN 2? These IP's belong to the same network so why would you ever use another VLAN? You wouldn't...ok so do this

    VLAN 1 - 192.168.1.0/24
    VLAN 2 - 192.168.2.0/24

    Ok, now how can a client on VLAN 1 communicate with a client on VLAN 2? What is needed to allow this communication to take place? You could make it even easier and use one L3 switch for this test but again, what do we need for this to take place?


    ^This is what I was thinking, too...
    A+, N+, S+, CCNA:RS, CCNA:Sec

    "In high society TCP is more welcome than UDP. At least it knows a proper handshake" - Ben Franklin

    2019 Goals: CCNP:RS & relocate to St. Pete, FL!
  • networker050184networker050184 Mod Posts: 11,962 Mod
    As your test has shown (when you do it right :)) tags are only carried on trunks. So you can bridge two VLANs together by doing this. Probably not the best thing to do in a production environment, but it will work.
    An expert is a man who has made all the mistakes which can be made.
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