10-09-2008 10:37 AM - edited 03-03-2019 11:51 PM
An issue just crept up and I hoping to post here for some clarification.
We have multiple vlans but only two are being effected.
vlan 26 - 10.10.26.x
vlan 27 - 10.10.27.x
both configured with ip helper-address 10.10.16.45
Nobody currently can recieve dhcp addresses on the 26 but if I turn off the helper address on the 26 vlan they recieve 10.10.27.x addresses.
If I turn the helper back on the 26 and turn it off on the 27, 27 users get a 26 address.
Would this be an issue on the 6500 or is this a problem with a possible rogue dhcp server? Or for that matter a problem with our DHCP server? (10.10.16.45 is the only authorized dhcp server on 2k3 box)
10-09-2008 11:19 AM
Has anything changed in your network? Are these new vlans? Have DHCP servers changed? Do you run individual subnets for each?
--John
10-09-2008 11:23 AM
Nothing has changed and these are not new vlans. DHCP server has not changed either. Each are individual subnets.
-Jeff
10-09-2008 11:22 AM
If you turn off ip helper-address on Vlan 26, devices on that subnet shouldn't get any address as the initial DHCP request is a broadcast which remains within the same Vlan.
If they are getting an address, your assumption is correct, there is a DHCP server in the subnet. You can verify the DHCP server in Windows by using IPCONFIG /ALL. There is a DHCP Server entry listed under the interface that obtained the dynamic address.
HTH,
__
Edison.
10-09-2008 11:30 AM
LOL! There's a test question in there somewhere. :-)
10-09-2008 11:25 AM
are you running DHCP locally?
Is there another place that has the helper address?
When you turn the ip helper off on Vlan 26 is the command still on vlan 27 and do the people attached to that vlan get their IP's? Are both affected at the same time, and if you turn off the helper on vlan 27 do you get the IP address on Vlan 27?
10-09-2008 11:44 AM
Nowhere do I see ip helper addresses anywhere else. No other boxes using 10.10.16.45 (dhcp) out there. (When I disconnect the DHCP box I get no (ping) responses)
vlan 26 user>vlan 26 port>ip helper-address on = no address
vlan 27 user>vlan 27 port>ip helper-address on = 10.10.27.x address
vlan 26 user>vlan 26 port>ip helper-address off = 10.10.27.x address
vlan 27 user>vlan 27 port>ip helper-address on = 10.10.27.x address
vlan 26 user>vlan 26 port>ip helper-address on = 10.10.26.x address
vlan 27 user>vlan 27 port>ip helper-address off = 10.10.26.x address
10-09-2008 11:49 AM
Here is the config on the 6500 for the vlan interfaces:
interface Vlan27
ip address 10.10.27.1 255.255.255.0
ip helper-address 10.10.16.45
no ip unreachables
appletalk cable-range 27-27 27.1
appletalk zone Business
appletalk getzonelist-filter 602
mls ip directed-broadcast exclude-router
interface Vlan26
ip address 10.10.26.1 255.255.255.0
ip helper-address 10.10.16.45
no ip unreachables
appletalk cable-range 26-26 26.1
appletalk zone Business
appletalk getzonelist-filter 602
mls ip directed-broadcast exclude-router
(Yes we still use appletalk!) :)
10-09-2008 11:57 AM
Why do you need to forward directed-broadcasts?
mls ip directed-broadcast exclude-router
It's due to the AppleTalk network?
Remove that command and see if the DHCP issue get resolved.
HTH,
__
Edison.
10-09-2008 12:04 PM
Removed the command but still no go.
We have around 60 vlans all using the 10.10.16.45 as the helper with no problems. All are using appletalk zones as well.
These 2 vlans are the only ones with this problem.
These vlans are not new either. It just started yesterday with these vlans being well over three yrs old.
10-09-2008 12:10 PM
vlan 26 user>vlan 26 port>ip helper-address off = 10.10.27.x address
vlan 27 user>vlan 27 port>ip helper-address on = 10.10.27.x address
vlan 26 user>vlan 26 port>ip helper-address on = 10.10.26.x address
vlan 27 user>vlan 27 port>ip helper-address off = 10.10.26.x address
Both scenarios - ipconfig/all state the dhcp server as 10.10.16.45
10-09-2008 12:54 PM
The configs seems fine and I have no explanation other than a switch failure. Try reloading the switch with ip helper-address configured under each interface and report back with results.
HTH,
__
Edison.
10-09-2008 06:51 PM
try to re-create vlan.
may be it work
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