quick question on Vlans
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Thread: quick question on Vlans

  1. #1
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    quick question on Vlans

    Can you have multiple subnets on one vlan?

    Ex.
    subnet 192.168.1.0 and subnet 192.168.2.0 on VLAN 1

  2. #2
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    yeap, but it is odd, inst it? why on same (virtual) lan you want 2 diferent ip networks?
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  3. #3
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    Yes it is odd, I was just wondering because if two subnets are on one vlan and since it is possible, that would mean you would see broadcasts from both subnets which seems really weird to me. I have never seen that before.

  4. #4
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    Its the same of putting 2 diferent sets of ip (diferent networks) on same lan segment. you can do it. but you can have "weird" effects....
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  5. #5
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    Am I missing something here? A VLAN is a broadcast domain; how can it have more than one subnet, thereby implying more than one broadcast domain? Wouldn't this screw everything up, not just have "weird" effects?
    And how do you put several different ip networks on the same lan without dividing them into vlans?

  6. #6
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    Ok now i'm more confused? Can you have two subnets on the same vlan or not?
    the reason i asked in the first place is because I saw on example on a webpage where
    ip address 192.168.1.0 was on VLAN 40 and 192.168.2.0 was also on VLAN 40 and then one of them got moved to a different VLAN.

    SO i would love to know for sure if this is possible or not?

  7. #7
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    Look at the definition. http://www.webopedia.com/TERM/V/VLAN.html

    VLANs can be subnets or supernets (http://www.webopedia.com/TERM/C/CIDR.html). So technically you could have 192.168.1.0 - 192.168.15.0 on the same VLAN. Kind of a big broadcast domain, but it'd work. If you split the network up due to growth and the fact that someone didn't think about it too much then you could have a scenario where you need to move hosts to a different VLAN. Seems to me to be bad planning.
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  8. #8
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    Great thanks!

  9. #9
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    Originally posted here by KeyserSoze
    Am I missing something here? A VLAN is a broadcast domain; how can it have more than one subnet, thereby implying more than one broadcast domain? Wouldn't this screw everything up, not just have "weird" effects?
    And how do you put several different ip networks on the same lan without dividing them into vlans?
    No, it would still be a single broadcast domain: a broadcast domain only represents the "area" in which a broadcast will propagate. There's nothing to say that these broadcasts must concern a single subnet. In fact, broadcast domains are layer 2 entities while subnets are layer 3 entities so they have no real interdependencies...

    As to having multiple subnets on the same lan segment, it wouldn't be any diffrent than a lan segment that connects two routers that route multiple subnets. What would happen is that all hosts on the lan would receive every subnet's packets but the routing software of every hosts would drop packets that aren't destined to the subnet it is a "member" of since there wouldn't be any local routes for them (or, supposing ipforwarding is enabled, it would send them to the default gateway).


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  10. #10
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    Originally posted here by thekit
    ip address 192.168.1.0 was on VLAN 40 and 192.168.2.0 was also on VLAN 40 and then one of them got moved to a different VLAN.
    What are the subnetmasks? There's no way to tell if these are 2 subnets or just 1.

    If the subnetmask is 255.255.255.0 it's 2 subnets but if it's 255.255.252.0 it's 1 subnet.
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