Significance of the VLAN IP address

Posted on 2012-09-19
Last Modified: 2012-09-22
Hi, Please advise

We are having odd problems on 1 floor. We have VLANS for each floor - Cisco 2960's. We have Cisco 3750 Core Switch's. Setup by Cisco engineer. On that core are all the floor VLAN IP's.(data vlan) On the troubled floor - its (VLAN ID is 213(data vlan)) - This has the VLAN IP in the core as such

The 1 difference with this floor (3) is that on the floor switch stack it (unlike the other floor stacks) has the VLAN IP listed as for vlan 213. - so core .99 and floor stack .98 for the same vlan?

So I guess im asking - what is the significance of the VLAN IP - or is this just significant for management (eg to telnet to the VLAN) ? - The odd behavior on this floor - is ping timeouts - a voip phone not getting dhcp address (vlan issue) - some general network type issues. - So with this mismatch in IP VLAN for 213 - is this a possible cause - maybe just a typo by Cisco engineer. - None of the other switches on the other floors have 2 different vlan IP's

I'm waiting to hear back from engineer - just need clarification please
Question by:philb19
    LVL 50

    Expert Comment

    by:Don Johnston
    All devices in the same VLAN will need to be on the same IP network.

    Author Comment

    Thanks donjohnston - so im right in saying that the IP network is defined by the IP address assigned to the VLAN - therefore the mismatch is the likely cause of strangeness? - the subnet/network - 192.168.3 is the same - but the .99 and .98 difference is a problem?
    LVL 50

    Accepted Solution

    It's hard for me to determine from your post. But unless there are discontiguous VLANs (which would be unusual and confusing), every device in a specific VLAN should have an IP address consistent with the other devices on that VLAN.

    And devices on other VLANs should have IP addresses that are on different IP networks.
    LVL 21

    Expert Comment

    It is not necessary for every switch to have an IP address in every VLAN, but it comes in handy for using the ping command to troubleshoot connectivity issues.  Since this one switch, that is having problems, has an IP in VLAN 213, it sounds like the previous tech was trying to troubleshoot a problem.  Maybe the one you're dealing with now.  Do you have an network diagram and a listing of all IP subnets/VLAN's?
    LVL 1

    Expert Comment

    How about a cleaned config from the core and the trouble floor, maybe throw a working floor's config in there for good measure.

    I think one of two things is going on with this post, either you're confused with IP or we're all confused by your post.  Not to sound condescending, if it's the first maybe you should hit up a NET+ class at minimum.  It could be beneficial.

    Author Closing Comment

    The problem was layer 3 routing (dhcp switch was not pingable)- not vlan -

    i thought it was vlan as a POE phone was getting power but not IP address from dhcp/broadcast - phone was in fact on same vlan as voip dhcp switch - so could have got a an ip despite the switch it was on not being able to ping dhcp switch. - the reason phone not working turned out to be the patch lead - power ok over some copper pair - but data pair failing hence no ip address from dhcp

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