networking titbits: vlans and no vlans

durga ch

durga ch

@durga-TpX3gO • Oct 26, 2024
ok, here is the scenario

pc1<-->sw1<-->sw2<-->pc2
1)will ping from pc1 to pc2 work?? why?
2)i configure pc1<-->sw1 interface in vlan 100 and sw1's interface to sw2 interface in vlan 100, but not vice versa ie Sw2 to Sw1 interface has no associated vlan
i DONT configure sw2<-->pc2 interface in vlan 100, now will my ping work??
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  • Rahul Jamgade

    Rahul Jamgade

    @rahul-yHGH3D • Feb 19, 2012

    1. In non-vlan scenario it will work provided that the PC1 and PC2 have same ip address range i.e. network address (subnet) remains same. Reason is switch is layer 2 device and it will have same broadcast domain even if switches are interconnected.

    2. In the scenario the vlan is configured for PC1 that is be terminated on sw1 port that is part of vlan100 and the PC2 and its corresponding port is not part of any vlan , that means PC2 is part of vlan0. Generally if the port is not part of any vlan than it is supposed to be part of vlan0. Also the ip range of vlan100 will be different from other vlan and hence any traffic that has to travel between 2 vlans has to go through router and the traffic rules allowed on router.
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  • durga ch

    durga ch

    @durga-TpX3gO • Feb 19, 2012

    Hi Rahul,
    IN scenario 1, sinc everything are on same network the pings will happen.
    In second case, I have not menioned any presence of router. I am not talking about a scenario where the two PCs are in different LANs and you might want to implement router on stick, I am talking about the two PCs being in same network.
    This is more of L2 issue than of L3.
    As per my observation and tests, The pings will be just fine.
    VLAN is basically a broadcast domain local to a switch, SW1 though has its outgoing port to SW2 in vlan 100, any packet recieved for VLAN 100 will be sent to this interface, but unless and until the link between SW1 and SW2 is configured as a truck , this vlan ID holds no importance for the other siwtch.
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