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DHCP relay on 3Com 5500G

Posted on 2009-12-30
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Last Modified: 2012-05-08
Please I need a step by step guide to configure two 3com 5500g for DHCP relay (ip helper).

I have a W2008 DHCP server that have 2 scope (ScopeVLAN100 and ScopeVLAN200)

ScopeVLAN100 is 10.10.100.0/24
ScopeVLAN200 is 10.10.200.0/24

DHCP server is connect on SWITCH2 in VLAN 1000
Clients(1) are connect on SWITCH1 in VLAN 100
Clients(2 are connect on SWITCH1 in VLAN 200

All SWITCH1 VLANs are routed to SWITCH2 VLAN 1000 (dhcp)

I have to assign a correct DHCP address to DHCP supplicant.

Thanks in advance.
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Question by:marcokrecic
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by:Donald Stewart
ID: 26151652
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JanSc earned 2000 total points
ID: 26152614
Simple:
Copy-paste, after xxx have been changed into needed IP adresses:


dhcp-server 1 ip  xxx.xxx.xxx.xxx (ip adress dhcp server in vlan 1000

interface Vlan-interface100
 ip address 10.10.100.xxx 255.255.255.0
 dhcp-server 1

interface Vlan-interface200
 ip address 10.10.200.xxx 255.255.255.0
 dhcp-server 1

That's all
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by:marcokrecic
ID: 26214158
I have configure the switch:

dhcp-server 1 ip 10.10.0.100

interface vlan-interface 100
    ip address 10.10.100.1
    dhcp-server 1

interface vlan-interface 200
    ip address 10.10.200.1
    dhcp-server 1

interface vlan-interface 1000
    ip address 10.10.0.1

on the dhcp server (w2k8) :

a superscope with
   scope 100   (10.10.100.2---> 10.10.100.254)
   scope 200   (10.10.200.2---> 10.10.200.254)
     

the first time the dhcp assign a correct ip address (in correct network)
but next time when i connect the same client to a different vlan (200) the dhcp server assign an ip address in Vlan 100

I don't understand

Please help me
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Expert Comment

by:Rick_O_Shay
ID: 26223631
Did the server maybe register what the mac of that PC was from when it was on the other network and something needs to be flushed to allow it to show up on the other subnet now?
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Author Comment

by:marcokrecic
ID: 26224016
I manually delete the previous lease from dhcp server but after the ipconfig /renew on the client the dhcp server lease the old ip in the wrong vlan.

is possible to disable the cache of mac address?
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by:Rick_O_Shay
ID: 26228541
Sorry, I don't know.
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by:JanSc
ID: 26272455
Only thing i can suggest is to check gateway of DHCP server, and/or vlan port settings of PC's on the switch. Normally this setup should work, and on 5500 its no need for flushing ARP table to make it work.

Ie if your DHCP server is still directly attached in vlan 100 or 200 (untagged) it will lease a vlan 1000 ip adress.
It's the 5500 who must transfer the dhcp broadcast of the PC (give me an IP) towards the DHCP server (UDP-Helper process). So the 5500 needs a direct connection in vlan 1000 to reach the DHCP server, and ask for ip adresses in vl100 an 200, which it will then broadcast to de PC's
 
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by:JanSc
ID: 26272459
Extra comment: Which firmware version of 5500 are you using? I recommend 03_03_01s56, as many previous problems have been eliminated.
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