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Layer 2 IP addressing and VLANS

Discussion in 'Routing & Switching' started by Pete01, Aug 15, 2005.

  1. Pete01

    Pete01 Kilobyte Poster

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    Having a bit of trouble getting my head around the concepts of VLANS, IP addressing and switches.

    According to my course materials layer 3 switches are not covered in the CCNA syllabus at this time.

    I will read the chapter a few more times but I could use a bit of help. As I understand it at the moment VLANS are created on switches as separate virtual LANs even though they are going through the same physical switch.

    As they are on different logical LANS they can not communicate with each other and access different VLANS, if you want to conenct the different VLANS as IP segments you will need a router to act as a default gateway.

    I'm having difficulty with understanding how layer 2 devices can use layer 3 addressing, I'm sure it's got something to do with protocols that function at the LLC sublayer or layer 2, can anyone point me in the direction of some reading on this?
     
    Certifications: MCP (NT4) CCNA
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  2. Phoenix
    Honorary Member

    Phoenix 53656e696f7220 4d6f64

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    the point is they are not

    the layer 2 device is not using layer 3 addresses, thats why you need a router to route between vlans (a layer 3 switch is a router and switch all in one, operating at wirespeed)

    a layer2 switch working with vlans is still purely operating with mac addresses, its just segmenting it up and preventing access amongst the seperate vlans, a layer 3 device is required to communicate between them, and thus work with layer 3 addresses
     
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  3. tripwire45
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    tripwire45 Zettabyte Poster

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  4. ffreeloader

    ffreeloader Terabyte Poster

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    I gotta agree. They are pretty cool stuff indeed.
     
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  5. Pete01

    Pete01 Kilobyte Poster

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    Thanks for the replies, I'm getting my head round the VLAN thing slowly but surely.

    What confused me initially was at the end of the chapter I'm reading on switching and VLANs it shows some switch configuration commands for setting up VLANs and assigning them IP addresses.

    I just saw IP configuration on a layer 2 device (on the assumption that layer 3 switches are not relevant here), assiging VLAN IP addresses, IP domain names and it threw me a bit.

    For example if you had a 24 port layer 2 switch and 3 VLANS, you don't want them to be able to see each other, no need for a router, just 1 'flat' broadcast domain, you can separate them off by assigning different VLANs using IP.

    The whole IP at layer 2 thing is still foxing me a bit :blink - I'll just go with it for the meantime I'm sure my understanding will click into place at a later stage.
     
    Certifications: MCP (NT4) CCNA
    WIP: 70-669, Learning MSI packaging
  6. Phoenix
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    Phoenix 53656e696f7220 4d6f64

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    you dont need to assign the vlan an ip address i believe
    but for management purposes this is useful, also often there is a dedicated management vlan for that kind of traffic

    justh elps you ping the 'vlan' interface to check its alive, as well as other such things (SNMP, etc)
     
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  7. simongrahamuk
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    simongrahamuk Hmmmmmmm?

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    I gotta agree there!

    I had a problem tyring to get my head around how VLANs worked, it wasn't until I actually installed a couple in a lab that I actually got my head around how they work.

    8)
     
  8. ffreeloader

    ffreeloader Terabyte Poster

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    It appears to me that you're confusing some basic issues so let's start at basics here.

    What do you mean by "IP domain name"?

    What is a broadcast domain?

    What do you mean by "assigning VLAN IP addresses"?

    How does a switch keep track of what computer is attached to which of it's ports?
     
    Certifications: MCSE, MCDBA, CCNA, A+
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  9. Pete01

    Pete01 Kilobyte Poster

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    I know that switches keep track of connected devices by MAC addresses, hence my confusion over the whole leyer 2-layer 3 thing. By domain name I meant VTP domain, a broadcast domain I've learnt is a single subnet.

    I've decided to stop chasing my tail over this and move on and save the questions for the lab, I think it's taking up more of my study time than it should be.

    I'm in a 2950 switch now hosted in Sweden. I just followed an excercise to create a vlan, give it an IP and assign it to a port on the switch. Here's some of the output from the session complete with mistakes :p :

    The 2950 doesn't have the IP menu that the 1900 does which is what initially threw me into such confusion.

    I've spent 2 days of annual leave on switching now so I think I'm going to switch (haha!) to something else and come back to it later.

    Thanks for all the help with this, I do have a weekend lab bootcamp next month to do all this under instruction. :D
     
    Certifications: MCP (NT4) CCNA
    WIP: 70-669, Learning MSI packaging
  10. Jonathan

    Jonathan Nibble Poster

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    where abouts is your bootcamp?
     
    Certifications: CCNA
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  11. Pete01

    Pete01 Kilobyte Poster

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    Milton keynes.

    Send me a PM if you'd like the link.
     
    Certifications: MCP (NT4) CCNA
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  12. Jonathan

    Jonathan Nibble Poster

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    I went on that course you should find it useful
     
    Certifications: CCNA
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