DHCP Multiple IP Scope

Muhammad Zahid · ‎06-02-2016

We have multiple data and voice VLANs and accordingly separate DHCP scopes are defined in Microsoft based DHCP server. On core switch, for each vlan interface (svi) ip helper-address command is configured with correct DHCP server. Now randomly user machine are receiving incorrect IPs for example sales teams are receiving IPs from marketing IP Pool however user machine are configured in correct vlans as access ports, any help

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Mark Malone · ‎06-02-2016

If it was my issue I would take an effected user as an example and capture the wireshark on both sides at the MS server and at the client side or try and debug ip dhcp detail , make sure the requester is sending the correct information in the packet when he looks for the ip and then check exactly what's coming in the packet from the MS side , this should tell you which side is not working correctly. The only way to see whats going on is to check at the packet level whats happening

I would first confirm the scopes are correct on the MS server , nothing irregular and make sure correct gateway etc set

Muhammad Zahid · ‎06-05-2016

Hi Mark,

Thank you for our response, scope on MS Server are correctly configured even i tried by setting up DHCP Server on Cisco switch but the results are same; now i will capture packets and will share the analysis.

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Muhammad Zahid · ‎06-06-2016

Packet capture shown that it’s another DHCP that is creating problem so I need your expert advice to implement IP snooping.

We have 2 core switches that run HSRP and under access layer my DHCP server is connected, DHCP is running on VM that is part of a cluster so I have to identify what ports from that switch need to be put as trusted ports so I am going to do following.

enable IP dhcp snooping on all switches including cores and access layer.
add required vlans in dhcp snooping
declare all switches trunk ports as trusted ports.
add DHCP server ports (VM Host) as trusted ports.

Command that I need to run on each switch global mode.

ip dhcp snooping
ip dhcp snooping vlan 10,20,30
no ip dhcp snooping information option

For Trusted ports.
ip dhcp snooping trust

On our Microsoft base DHCP server we enable MAC filtering so for guest and few other test VLANs we setup DHCP server on Core switch so do I need to perform any additional task to make cisco base dhcp scope make working.

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paul driver · ‎06-02-2016

Hello

Do the dhcp server scopes match the SVI l3 Subnets, or do they overlap?

Do you have secondary addressing?

res

Paul

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Paul

Muhammad Zahid · ‎06-05-2016

Yes Paul, SVI sublets are exactly matching with DHCP scopes, what you mean by secondary addressing please elaborate.

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