Wendell Odom's ICND1 book query.

hassantalal785hassantalal785 Member Posts: 47 ■■□□□□□□□□
in CCNA & CCENT
I didn't understand something i read in ODOM's CCNA book . It was written in the book :


"For example, if a network had 30 access layer switches, and the network
engineer decided that each access layer switch should be cabled directly to every other
access layer switch, the LAN would need 435 cables between switches! "

Why 435 cables would be used ? If there are 30 switches to be interconnected then 30 cables should be needed.
Kindly explain .
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Comments

  • IristheangelIristheangel Mod Posts: 4,133 Mod
    Interconnected = mesh network. He's talking about a fully mesh network where EVERY switch is directly connected to the remaining 29 switches. The formula to determine this is (N x (N-1))/2

    (30 x 29)/2 = 435
    BS, MS, and CCIE #50931
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  • hassantalal785hassantalal785 Member Posts: 47 ■■□□□□□□□□
    Oh yes . Now i understand thanks a lot
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  • hassantalal785hassantalal785 Member Posts: 47 ■■□□□□□□□□
    I have another query if you m mind. Suppose i have a switch with only layer 2 functionality and not a layer 3 switch .Its port 1 is configured as vlan 1 and its port 2 as vlan 2 . If port1's PC send a packet to Port 2's PC , would a Router have to be involved as both ports are on separate Vlans or not ?
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  • DiggsDiggs Member Posts: 97 ■■□□□□□□□□
    Yes, if a PC connected to a switchport which is assigned to vlan 1 wanted to send a packet to a PC assigned to a different vlan it would need to send the packet to its default gateway (router). The PC in a different vlan would be in a separate subnet
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  • IvanjamIvanjam Member Posts: 978 ■■■■□□□□□□
    Diggs wrote: »
    Yes, if a PC connected to a switchport which is assigned to vlan 1 wanted to send a packet to a PC assigned to a different vlan it would need to send the packet to its default gateway (router). The PC in a different vlan would be in a separate subnet

    Someone correct me here if I am wrong but, offhand, from my limited perusal of the CCENT material, the two PC's can very well be in the same subnet and still not be able to communicate, as vlan segregation occurs at layer 2 of the OSI model.
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  • MrXpertMrXpert Member Posts: 586 ■■■□□□□□□□
    Ivanjam wrote: »
    Someone correct me here if I am wrong but, offhand, from my limited perusal of the CCENT material, the two PC's can very well be on the same subnet and still not be able to communicate, as vlan segregation occurs at layer 2 of the OSI model.

    Yes VLANS are verymuch a layer 2 implementation.A VLAN=a subnet=broadcast domain
    I'm an Xpert at nothing apart from remembering useless information that nobody else cares about.
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  • IvanjamIvanjam Member Posts: 978 ■■■■□□□□□□
    MrXpert wrote: »
    Yes VLANS are verymuch a layer 2 implementation.A VLAN=a subnet=broadcast domain

    So, I take it that you must first create the vlans that you need, then assign different subnets to each vlan?
    Fall 2014: Start MA in Mathematics [X]
    Fall 2016: Start PhD in Mathematics [X]
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  • MrXpertMrXpert Member Posts: 586 ■■■□□□□□□□
    Yes this is how I have done it.
    I'm an Xpert at nothing apart from remembering useless information that nobody else cares about.
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