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Wired Networks Thread, VLAN/DHCP/DNS issue in Technical; Wondering if anyone can help... I have recently upgrade our DC to some new 2012R2 VMs on hyper v and ...
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    VLAN/DHCP/DNS issue

    Wondering if anyone can help...

    I have recently upgrade our DC to some new 2012R2 VMs on hyper v and have migrated the roles and services across.

    Our clients are now getting all the right details from the DHCP server (Router for their VLAN, DNS servers etc) but aren't able to connect to the DNS servers thus not get logon servers or access the internet. The VLANs are configured with an IP and also with a helper ip address to get to the dhcp. They can ping external IP address, but not the DNS server. If you put in google's public fns, you can access the internet.

    Any one have any thoughts?

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    synaesthesia's Avatar
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    am I right in assuming the DNS servers are not the DHCP servers then?

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    nope the dns servers are the dhcp servers!

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    synaesthesia's Avatar
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    Ok - start simple, have you checked firewall? Even in place upgrade re-enabled the firewall when we moved up to 2012 R2.

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    nothing that simple I'm afraid
    Firewall off on the DCs and the hyper hosts

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    synaesthesia's Avatar
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    what networking gear are you using, so we can get an idea of the vlan and routing setup?

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    Force10 Core switch (3 Switches stacked)

    VLAN Config looks like this :

    interface Vlan 10
    name Retouch_VLAN_10
    ip address 10.101.10.1/24
    tagged GigabitEthernet 1/0,2
    tagged GigabitEthernet 2/1
    untagged GigabitEthernet 2/37-43
    ip directed-broadcast
    ip helper-address 10.101.60.11
    no shutdown

    It all worked ok before we moved over!

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    synaesthesia's Avatar
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    Seems odd, one can only assume that it's software level. The network drivers in the upgraded OS haven't managed to detect and set VLAN accordingly have they?

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    they were actually new VMs, I meant that I had upgraded the domain

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    ADMaster's Avatar
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    I’m not familiar with that gear, but can the two vlans route between each other. Your dhcp server is in a different subnet, but you do not provide that subnet / vlans configuration.
    Some switches you have to tag what vlans are allowed on the trunk port.

    If you go to vlan 60 or set yourself a static IP in the 10.101.60.0/24 range can you access dns then?
    With this being a new server install verify that the IP subnet is correct. When you enter an IP in the 10.x range it defaults it 255.0.0.0 or /8 you need 255.255.255.0 or /24 with the config you referenced above.

    Can other vlans access the dns server? If no other vlans can use dns see if the service is running or if there is any errors in event log.

    Also this is probably not the case with the no logon servers, but…
    Can your clients access the dns server but the dns server is not configured for forward the request? So effectively they do not have DNS.

    Nslookup is your friend,
    Cheers

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    DMcCoy's Avatar
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    Route issue, either the server or clients are not using the relevant switch IP for their gateway. DHCP requests are forwarded via the helper mechanism, the rest of the traffic is not.

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    Ok so after doing suggested things:

    I have put wireshark on the DNS server. I can see the packet come in with the request from the IP address of the device and then go out.
    When the device is on the same subnet (VLAN60), all is good.
    If I put device onto VLAN70 DNS receives and makes reply but not reaching the device. When DNS is set to 8.8.8.8 then connects to site.
    Send a ping to the DNS, can see it come in and leave the server, but never reaches device.
    What is odd is that some devices on the 10.101.60.X/24 network can be pinged/ give me a route, but servers cannot...

    In my head this would be that a route does not exist from the 10.101.60.0/24 network to the others.
    This is what is configured on the switch:
    Gateway of last resort is 10.101.2.2 to network 0.0.0.0

    Destination Gateway Dist/Metric Last Change
    ----------- ------- ----------- -----------
    *S 0.0.0.0/0 via 10.101.2.2, Vl 2 1/0 00:00:05
    C 10.101.2.0/24 Direct, Vl 2 0/0 2d19h
    C 10.101.10.0/24 Direct, Vl 10 0/0 8w6d
    C 10.101.20.0/24 Direct, Vl 20 0/0 8w6d
    C 10.101.25.0/24 Direct, Vl 25 0/0 8w6d
    C 10.101.30.0/24 Direct, Vl 30 0/0 8w6d
    C 10.101.40.0/24 Direct, Vl 40 0/0 8w6d
    C 10.101.41.0/24 Direct, Vl 41 0/0 8w6d
    C 10.101.50.0/24 Direct, Vl 50 0/0 8w6d
    C 10.101.60.0/24 Direct, Vl 60 0/0 8w6d
    C 10.101.70.0/24 Direct, Vl 70 0/0 8w6d

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    Duke5A's Avatar
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    You don't have multiple network adapters in the DNS server do you?

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