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How can i stop DHCP being served to a group of ports on one particular switch on a particular vlan?

How can i stop DHCP being served to a group of ports on one particular switch on a particular vlan?

How can i stop DHCP being served to a group of ports on one particular switch on a particular vlan?
How can i stop DHCP being served to a group of ports on one particular switch on a particular vlan?
2025-01-24 12:23:56

I have need to prevent devices with a specific VLAN tag from receiving DHCP on a group of ports on one particular switch - they instead must be set as statics.  I want to force this so the users must set a static on the device before it can work rather than relying on DHCP.  I need DHCP to continue to serve all the rest of the network as normal for that VLAN. 

 

Things I have tried:

 

Switch ACL to prevent "Network - Tech" > DHCP Server IP Ports 67-68 UDP applied to only that group of switch ports specifically

Switch ACL to prevent DHCP Server IP Ports 67-68 UDP > "Network - Tech" applied to only that group of switch ports specifically (reverse of above)

 

Switch ACL to prevent UDP Ports 67-68 > IPgroup_Any applied to only those ports

Switch ACL to prevent IPgroup_Any > UDP Ports 67-68 applied to only those ports (reverse of above)

 

I have tried the above 4 ACLs using the DHCP servers source switch port instead

 

I have tried using the DHCP servers MAC address in a MAC group, and used ACLs in both directions to and from it.

 

I still, always get DHCP served on those ports!

 

WHY ?????

 

The only way i can seem to block DHCP is a blanket UDP 67-68 > IP_Group_Any applied to all switch ports across entire network.

 

Can anyone assist?

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#1
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4 Reply
Re:How can i stop DHCP being served to a group of ports on one particular switch on a particular vlan?
2025-01-26 08:33:13

Hi @GRL 

Thanks for posting in our business forum.

Prevent the GW IP instead of any. Block the GW IP(DHCP server IP) in that broadcast range.

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#2
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Re:How can i stop DHCP being served to a group of ports on one particular switch on a particular vlan?
2025-01-26 08:38:36

  @Clive_A 

 

I have tried that

 

ACL

Block UDP 67-68 <> GW IP. those switch ports only

 

DHCP still passes!

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#3
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Re:How can i stop DHCP being served to a group of ports on one particular switch on a particular vlan?
2025-01-26 08:46:32

Hi @GRL 

Thanks for posting in our business forum.

GRL wrote

  @Clive_A 

 

I have tried that

 

ACL

Block UDP 67-68 <> GW IP. those switch ports only

 

DHCP still passes!

DHCP IP still got assigned to them the clients?

Rule 1 IP-Port subnet of this VLAN, port UDP 67 68

Rule 2 GW IP to VLAN, port 66 67. The GW IP means the IP in that VLAN. Not the default VLAN 192.168.0.1, for example.

VLAN 10.0.0.0/24, IP is 10.0.0.1/24 if you configure it.

Best Regards! If you are new to the forum, please read: Howto - A Guide to Use Forum Effectively. Read Before You Post. Look for a model? Search your model NOW Official and Beta firmware. NEW features! Subscribe for the latest update! ☛Download Beta Here☚ ☛ ★ Configuration Guide ★ ☚ ☛ ★ Knowledge Base ★ ☚ ☛ ★ Troubleshooting ★ ☚ ● Be kind and nice. ● Stay on the topic. ● Post details. ● Search first. ● Please don't take it for granted. ● No email confidentiality should be violated. ● S/N, MAC, and your true public IP should be mosaiced.
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#4
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Re:How can i stop DHCP being served to a group of ports on one particular switch on a particular vlan?
2025-01-26 08:50:33

  @GRL 

 

Yes this is exatly what i tried

 

VLAN 6 (not management

GW IP 192.168.6.254

 

Switch ACL

 

192.168.6.0/24 UDP port 67-68  ..........  192.168.6.254 UDP port 67-68     Applied to Switch 3 ports 1-8 only

 

I tried it the other way around as well, and also as one and the reverse in a seperate acl

 

DHCP always passed.

 

DHCP doesnt pass if i apply the rule to all switch ports.  It only not works if i apply to a selection of ports on any particular switch.

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#5
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