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Here's the scenario:

I replaced 2 core switches (3550 catalysts - 12G) on Wednesday. I have configured the VTP and added the VLANs to the database.

My core and ethernet switches can ping to the DHCP server. However, (most) of the end users are not receiving IP addresses. I have verified that the FastEthernet ports are correctly configured for the appropriate VLANs.

Thank you for your help!

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  • Perhaps no ip dhcp relay information check is needed?
    – Ricky
    May 20, 2014 at 20:39
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin ♦
    Aug 8, 2017 at 20:14

2 Answers 2

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Assuming your DHCP server is on a different VLAN than your users, check that you have your ip helper correctly configured. On the SVI (Vlan interface) of your user vlans you should have

ip helper-address a.b.c.d

where a.b.c.d is the IP address of your DHCP server

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  • Thank you for the comment! My ip helper-address(es) are set up to route to the DHCP server, and I have confirmed they have the correct IP Address.
    – user218699
    May 18, 2014 at 0:20
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Ensure dhcp snooping and dhcp snooping trust isn't interfering with the server answers. If the switch(es) are acting as the inter-vlan router, they also need to be handling dhcp relay duty -- which will add giaddr (gateway) to requests so the server knows how to answer.

Eg. from my lab switches:

ip dhcp snooping vlan ...
ip dhcp snooping
interface Port-channel1
 switchport trunk allowed vlan ...
 switchport mode trunk
 ip dhcp snooping trust

(upstream of this cisco is a nortel switch, then an hp switch, and the dhcp server)

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  • Neither my core nor ethernet switches have dhcp snooping/trust enabled.
    – user218699
    May 16, 2014 at 20:59

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