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July 27th, 2021 13:00
How to disable DHCP server on management VLAN on Dell PowerConnect 5524
Hi there,
Maybe somebody can help me with this what seems to be quite simple but not with Dell
I have configured 2 DHCP pools on Dell PowerConnect 5524:
ip dhcp server
ip dhcp pool network 203
address low 10.203.0.10 high 10.203.0.20 255.255.255.0
default-router 10.203.0.1
dns-server 1.1.1.1
exit
ip dhcp pool network 204
address low 10.204.0.20 high 10.204.0.30 255.255.255.0
default-router 10.204.0.1
dns-server 1.1.1.1
exit
I use vlan 1 for management and it has a static ip address (I specifically want to keep it static) and NO pool created for it. Vlan 1 has it's own dhcp server running on the router (10.10.10.1)
!
interface vlan 1
name Management
ip address 10.10.10.16 255.255.255.0
!
However what I'm seeing is that if anything connects to vlan 1 and requests DHCP Address, switch is also getting involved sending NAK messages, resulting in host not being able to obtain an ip address from real dhcp server which is 10.10.10.1 Dump of WireShark:
wireshark dhcp dump
What am I doing wrong? Why is switch getting involved if it's not configured to serve IPs for this subnet? My question is how do I enable dhcp server on the switch for specific vlans only?
So far what I found is if I disable dhcp server on the switch. It will stop doing that. Would be good if I could disable dhcp server only on vlan1 for example.
no ip dhcp server
Teymur
teymur88
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11 Posts
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July 27th, 2021 14:00
Tried playing with DHCP Relay agent on the switch - but there is no joy. It's either DHCP Server or Relay will be working, not both of them
Teymur
DELL-Young E
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July 27th, 2021 22:00
Hi,
It seems like you need to configure extended ACL for subnet of VLAN 1 and block DHCP request
from their router
no ip dhcp server --> if the customer configure this commands , rest of dhcp pool will not work any more
teymur88
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July 28th, 2021 04:00
Hi there,
Thanks for your reply,
What I'm actually trying to do is to prevent switch acting as DHCP server for Subnet ov VLAN 1 only. And have it acting as DHCP for the VLANs I define.
Teymur
DiegoLopez
6 Operator
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2.7K Posts
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July 28th, 2021 07:00
Hello @teymur88,
As far as I know The DHCP client built into the PowerConnect has some limitations and can only provides service to the default VLAN.
If you need more advanced options you will need a DHCP server with scopes for each VLAN, and a switch with DHCP relay/ IP helper enabled on it.
Regards.
teymur88
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July 28th, 2021 08:00
Hello @DiegoLopez
The switch properly works as a DHCP server for multiple subnets - I have personally tested that. My problem is that the dhcp server function is only being enabled or disabled globally - meaning that it will either serve addresses for all vlans (which have ip addresses) or it won’t at all. I can’t find a way to disable or enable dhcp server function per vlan.
Teymur
DELL-Young E
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July 28th, 2021 20:00
Hi, also attaching a video for you just in case
Configure DHCP for each VLAN in DELL N-Series switches
teymur88
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August 2nd, 2021 01:00
Hi @DELL-Young E
Thanks for the video! I'm sorry, but I can't understand what's the point of it if that has nothing to do with the question I asked. I'll repeat my question again:
If I have a VLAN with ip address configured statically, and no dhcp pool configured for it, why the switch is getting involved into the DHCP traffic on that vlan if it's "got nothing to say" there.
In my case, as far as I know and understand there is no way on PowerConnect 5524 at least, to disable or enable DHCP server per vlan. It's either ENABLED GLOBALLY or DISABLED GLOBALLY. Reason to ask it here is to learn an expert opinion on this.
It seems like I ask something and get completely different thing in response.
Teymur.
DELL-Young E
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August 3rd, 2021 23:00
Hello, Teymur88. Sorry I have misunderstood your questions. My sincere apologies. Let us go back to what you said to doublecheck:
"However what I'm seeing is that if anything connects to vlan 1 and requests DHCP Address, switch is also getting involved sending NAK messages, resulting in host not being able to obtain an ip addressfrom real dhcp server which is 10.10.10.1 Dump of WireShark" ---> Can you please confirm that you don't want to connect any device on vlan 1 ?