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Switches, Hubs, and Modems
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DHCP across VLAN

Ramon Beringer
Occasional Advisor

DHCP across VLAN

Hi,
i am in big trouble here getting DHCP Responses across my 3500yl. I am now in the situation that i have 1 PC in VLAN 101 (10.101.1.0 255.255.255.0) discovering for an DHCP Address via Broadcast. Then the 3500yl forward that packet via Unicast to my DHCP Server in my Default VLAN 1 (10.1.0.0 255.255.0.0). Thats the good thing.

Then my DHCP Server is sending an DHCP Offer via BROADCAST but the 3500yl don't catch that Packet and move it into my VLAN 101.

Should the DHCP Server not response with an Unicast to my Switch?

Any "sh dhcp-relay" on my 3500 shows 0 0 0 0

LHG-HUB283# sh run

Running configuration:

; J8693A Configuration Editor; Created on release #K.12.57

hostname "LHG-HUB283"
web-management management-url ""
time timezone 60
time daylight-time-rule Middle-Europe-and-Portugal
module 1 type J86yyA
module 2 type J86xxA
module 3 type J8694A
ip routing
vlan 1
name "DEFAULT_VLAN"
untagged 1-A4
ip address 10.1.12.2 255.255.0.0
exit
vlan 101
name "WLAN-IM"
ip helper-address 10.1.110.59
ip address 10.101.1.1 255.255.255.0
tagged 1,A1-A2
exit
ip route 0.0.0.0 0.0.0.0 10.1.17.1
router ospf
area backbone
exit
spanning-tree
spanning-tree priority 5 force-version RSTP-operation
vlan 1
ip ospf 10.1.12.2 area backbone
exit
vlan 205
ip ospf 10.200.5.1 area backbone
exit

LHG-HUB283#

Thank you for any help,
Best Regards,
Ramon
2 REPLIES
Ramon Beringer
Occasional Advisor

Re: DHCP across VLAN

Hi,
I found the Error, it seems that Configuration don't work with Tiny DHCP Server V1.3. I take another DHCP (Linux) and now it works perfect.

Thanks,
Ramon
cenk sasmaztin
Honored Contributor

Re: DHCP across VLAN

hi Ramon

so you dhcp server in vlan 1 must be
ip address 10.1.12.3
subnet musk:255.255.0.0
default gateway :10.1.12.2
and connect switch on vlan 1 untag port

and you create on dhcp scobe for vlan 101
scobe name vlan 101
ip range 10.101.1.10......10.101.1.250
subnet mask:255.255.255.0
default gateway:10.101.1.1

and you write ip helper address on vlan 101
ip helper-address 10.1.12.3(dhcp nic address)
and ip routing enable on switch .

cenk...........

cenk