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Vlan Ip addresses

Discussion in 'General Cisco Certifications' started by wrathyimp, Sep 22, 2011.

  1. wrathyimp

    wrathyimp New Member

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    How can i know a VLAN has what ip range?

    Can any one give the command for it.

    Thanks
     
  2. cisco lab rat

    cisco lab rat Megabyte Poster

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    What equipment are you working on?

    Have you tried looking at the equipment makers web site?

    if you are working on cisco kit you can try the command

    switch#show ip int br

    Also it is polite to introduce yourself prior to making requests
     
    Certifications: Yes I pretty much am!!
    WIP: Fizzicks Degree
  3. wrathyimp

    wrathyimp New Member

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    Sorry,

    Totally new to cisco, just finished my studies, and trying out some placements, and got a temporary job, (little cash for experience) kinda stuff.

    Anyways, I have assigned a task to documenting all Network port Nos, ip address etc, so I need to check VLANs in the cisco switch, its catalyst 3550, are assigned what Ip address.

    I tried the mentioned command, but it only list the following:

    Interface IP-Address OK? Method Status Protocol
    Vlan1 192.168.0.3 YES NVRAM up up
    FastEthernet0/1 unassigned YES unset down down
    FastEthernet0/2 unassigned YES unset up up
    FastEthernet0/3 unassigned YES unset up up
    .
    ..

    so it not showing any ip address of the vlans, butwen i gve cmmand like show vlan, get list of vlans.
     
  4. cisco lab rat

    cisco lab rat Megabyte Poster

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    Right, first of all the 3550 is a Layer 3 device along with being a Layer 2 switch. Which means that the device will route along with switching.

    By the looks of it I don't think this device is routing unless there is a static default route. Not that you have been asked to find out. (Show ip route)

    I see that this box has one IP address on Interface Vlan 1, notice that I emphasise the Interface, this is called an SVI, "Switched Virtual Interface", in normal "no routing on the switch" setup this interface has an IP address so that you may remote to it using Telnet, SSH etc.


    You don't put IP addresses onto VLAN's, these VLAN's are layer 2 only

    Notice that there are two terms there, one is VLAN the other is INTERFACE VLAN, the first is Layer 2 the second is L3, on a 3550 switch the Layer 3 INTERFACE VLAN's with IP addresses can be used to route between VLAN's

    You have been asked to document the IP addresses, then simply write down what you see under "Interface Vlan 1", the output can be misleading as the INTERFACE VLAN 1, is listed as just VLAN, But it is listed under the Interface column. In your case this switch has the IP Addresss of 192.168.0.3 on INTERFACE VLAN 1

    If you want to list the layer 2 vlans then type the following

    switch#show vlan bri

    If you want to see what other cisco devices are connected to this switch type in:

    switch#show cdp neigbors

    If you want to see the state of your interfaces, up / down / speed / duplex type in:

    switch#show ip int status
     
    Last edited: Sep 22, 2011
    Certifications: Yes I pretty much am!!
    WIP: Fizzicks Degree
  5. Simonvm

    Simonvm Kilobyte Poster

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    That's your ip right there.
    Check the running-config for the VLAN1 interface and you're set, shouldn't be that hard to derive
     
    Certifications: MCITP: EST, MCDST, MCTS, A+, N+, CCNP, CCNA Wireless
  6. cisco lab rat

    cisco lab rat Megabyte Poster

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    Da ting is the whole concept of VLAN's verses INTERFACE VLAN can be a little confusing

    I see it all the time in the classroom. Create a L2 VLAN on a switch and it is assumed that the L3 INTERFACE VLAN must also be created, this will lead to various issues.

    On a L2 switch like my favourites the 2950 if you already have INTERFACE VLAN 1 in the up/up state with an IP address assigned, by creating say INTERFACE VLAN 3 (because you have created VLAN 3) and typing "no shut", the switch will believe that you wish to change the management VLAN from INTERFACE VLAN 1 to INTERFACE VLAN 3 and shutdown INTERFACE VLAN 1 along with stealing it's address. There can be only one L3 SVI on a L2 switch like a 2950 and that is only for maangement.

    On a L3 switch you only create the L3 INTERFACE VLAN's if you want those interfaces to be the GATEWAYS for the devices out of the. If you start creating L3 INTERFACE VLAN's all over the place it can lead to blackholing traffic.
     
    Certifications: Yes I pretty much am!!
    WIP: Fizzicks Degree
  7. wrathyimp

    wrathyimp New Member

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    What i understand, that this switch has the default vlan1, and the out vlans its showing are from the core switchs ie L2.

    They have two 4503 switches as core, and 3550 switches on different floors connecting via fiber optic.

    So i need to get the ip range from the core switch.
     
  8. cisco lab rat

    cisco lab rat Megabyte Poster

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    That is correct from what I see from your output the 3550 has an IP address of 192.168.0.3 on the INTERFACE VLAN 1

    You will have to run the same commands on the two 4503 switches at the core and note any IP addresses, same as you did on the 3550

    Yeap, just run the "show ip int brief"
     
    Last edited: Sep 22, 2011
    Certifications: Yes I pretty much am!!
    WIP: Fizzicks Degree
  9. Straylight

    Straylight Bit Poster

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    Ha, so true. I've not used layer 3 switches yet. But in my lab at home, that creating interface VLAN 2, interface VLAN 3 etc, when just wanting to add VLANS, on 2950s, caused me much puzzlement.
     
    Certifications: CCENT
    WIP: CCNA MS 70-680

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