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IP DHCP Helper-Address - Wrong Subnet

Chris Klimakhin
Occasional Visitor

IP DHCP Helper-Address - Wrong Subnet

Hello,

I am configuring a ProCurve 5406zl to provide DHCP relaying to several VLANS.

Here is the VLAN configuration:

===========================================

vlan 1
name "default"
untagged A10,A17,A22,A24-B12,B15-B24,Trk1
ip address 10.1.1.4 255.255.255.0
tagged A23,Trk2
no untagged A1-A9,A11-A12,A14-A15,A21,B13-B14
exit
vlan 2
name "Admin"
untagged A4-A6,A9
ip address 192.168.100.111 255.255.255.0
tagged A22-A23,B1-B10,B23-B24,Trk1
ip access-group "3" out
exit
vlan 3
name "Business"
untagged A1,A3
ip address 192.168.17.1 255.255.255.0
tagged A22-A23,B1-B10,B23-B24,Trk1
ip access-group "4" out
exit
vlan 4
name "Academic"
untagged A2,A7-A8,A11-A12,A15
ip address 172.16.0.1 255.255.0.0
tagged A22-A23,B1-B10,B23-B24,Trk1-Trk2
ip access-group "100" out
exit
vlan 5
name "Superintendent"
untagged A21
tagged A22-A23
no ip address
exit
vlan 10
name "AcademicWIFI"
ip helper-address 172.16.0.10
ip address 172.17.10.1 255.255.255.0
tagged A23
exit
vlan 11
name "GuestWIFI"
ip helper-address 172.16.0.10
ip address 172.17.11.1 255.255.255.0
tagged A23
exit
vlan 7
name "AcademicMain"
ip helper-address 172.16.0.10
ip address 172.20.8.1 255.255.248.0
tagged A14
exit
vlan 8
name "AcademicCH"
untagged B14
ip helper-address 172.16.0.10
ip address 172.20.16.1 255.255.255.0
exit
vlan 9
name "AcademicPNP"
untagged B13
ip helper-address 172.16.0.10
ip address 172.20.17.1 255.255.255.0
exit
dhcp-relay option 82 keep
ip route 0.0.0.0 0.0.0.0 10.1.1.1

===========================================

For some reason, not matter which VLAN I am on, I get the IP Addresses from the 172.16.8.0/21 scope. As you can see, B13 and B14 are configured for two different VLANs, but I am still getting IP Addresses from the "AcademicMAIN" subnet.

The DHCP server is configured correctly.

Also, IP Routing is enabled.
4 REPLIES
Pieter 't Hart
Honored Contributor

Re: IP DHCP Helper-Address - Wrong Subnet

>>> I get the IP Addresses from the 172.16.8.0/21 scope <<<

yes there is the problem /21.
Your Main and other subnets overlap
- you need multiple scopes /24
- you need to modify your main subnet so it's also /24

hth
Pieter
Chris Klimakhin
Occasional Visitor

Re: IP DHCP Helper-Address - Wrong Subnet

How so? 172.20.8.0/21 goes up to 172.20.15.255...
Chris Klimakhin
Occasional Visitor

Re: IP DHCP Helper-Address - Wrong Subnet

I can't use a /24 "Main" subnet because I have 1200+ hosts...
Marco Wessel
Valued Contributor

Re: IP DHCP Helper-Address - Wrong Subnet

Then you might need to change the two WiFi subnets. They currently overlap with your Main subnet, which can cause things like these to happen.