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ip helper-address passing DHCP to server but not back?

Posted on 2007-12-01
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Last Modified: 2008-04-23
I have two 3750 switches in a stack configuration. The Gig Switch is the data vlan, the 100 mbps switch is voice. DHCP on the voice VLAN through a server on the LAN VLAN is non-functional. Requests are getting to the DC but not getting back. I can see the leases in the DHCP control panel but phones/PCs get nothing on the voice VLAN. The DC can ping the voice subnet. If I remove the helper command, clients on the voice VLAN ports get a LAN IP. I've pasted the config below. Any thoughts?
!
version 12.2
no service pad
service timestamps debug datetime
service timestamps log datetime
service password-encryption
!
hostname 10-42-1-250
!
logging buffered 32768 informational
no logging console
enable secret 5
enable password 7
!
username backup privilege 15 password 7 0
aaa new-model
aaa authentication login default group tacacs+ local
aaa authentication enable default group tacacs+
aaa authorization console
aaa authorization config-commands
aaa authorization exec default group tacacs+ local
aaa authorization commands 1 default group tacacs+ if-authenticated
aaa authorization commands 15 default group tacacs+ if-authenticated
!
aaa session-id common
switch 1 provision ws-c3750g-24ts-1u
switch 2 provision ws-c3750-24p
system mtu routing 1500
ip subnet-zero
ip routing
no ip domain-lookup
!
!
!
!
no file verify auto
!
spanning-tree mode rapid-pvst
spanning-tree portfast default
spanning-tree extend system-id
spanning-tree vlan 1 priority 16384
spanning-tree vlan 2 priority 24576
!
vlan internal allocation policy ascending
!
interface GigabitEthernet1/0/1
 description Uplink to ASA
 spanning-tree portfast disable
!
interface GigabitEthernet1/0/2
!
interface GigabitEthernet1/0/3
!
interface GigabitEthernet1/0/4
!
interface GigabitEthernet1/0/5
!
interface GigabitEthernet1/0/6
!
interface GigabitEthernet1/0/7
!
interface GigabitEthernet1/0/8
!
interface GigabitEthernet1/0/9
!
interface GigabitEthernet1/0/10
!
interface GigabitEthernet1/0/11
!
interface GigabitEthernet1/0/12
!
interface GigabitEthernet1/0/13
!
interface GigabitEthernet1/0/14
!
interface GigabitEthernet1/0/15
!
interface GigabitEthernet1/0/16
!
interface GigabitEthernet1/0/17
!
interface GigabitEthernet1/0/18
!
interface GigabitEthernet1/0/19
!
interface GigabitEthernet1/0/20
!
interface GigabitEthernet1/0/21
!
interface GigabitEthernet1/0/22
!
interface GigabitEthernet1/0/23
 description Voice Equipment
 switchport access vlan 2
!
interface GigabitEthernet1/0/24
!
interface GigabitEthernet1/0/25
!
interface GigabitEthernet1/0/26
!
interface GigabitEthernet1/0/27
!
interface GigabitEthernet1/0/28
!
interface FastEthernet2/0/1
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/2
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/3
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/4
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/5
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/6
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/7
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/8
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/9
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/10
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/11
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/12
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/13
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/14
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/15
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/16
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/17
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/18
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/19
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/20
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/21
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/22
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/23
 switchport access vlan 2
 speed 100
 duplex full
!
interface FastEthernet2/0/24
 switchport access vlan 2
 speed 100
 duplex full
!
interface GigabitEthernet2/0/1
!
interface GigabitEthernet2/0/2
!
interface Vlan1
 ip address 10.42.1.250 255.255.255.0
!
interface Vlan2
 ip address 10.42.5.250 255.255.255.0
 ip helper-address 10.42.1.10
!
ip classless
ip route 0.0.0.0 0.0.0.0 10.42.1.254
no ip http server
!
tacacs-server host xxxxxxxxx
tacacs-server host xxxxxxxxxxxxxx
tacacs-server directed-request
tacacs-server key 7
radius-server source-ports 1645-1646
!
control-plane
!
!
line con 0
 password 7 0
line vty 0 3
 password 7 1
line vty 4
 password 7 0
line vty 5 14
 password 7 0
line vty 15
 password 7 0
!
ntp clock-period 36028772
ntp server 198.123.30.132
end
0
Comment
Question by:mrpez1
2 Comments
 
LVL 50

Expert Comment

by:Don Johnston
Comment Utility
So the phones are connected to the second switch (2/0/x)?
And with no ip helper-address on the VLAN2 interface, the phones get an IP address on VLAN1?

What port is the DHCP server connected to and does it have a scope for the 10.42.5.0 network?
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LVL 5

Accepted Solution

by:
mrpez1 earned 0 total points
Comment Utility
Issue resolved. I unplugged a third, uplinked switch and DHCP magically started working again. Plugging that switch back in did not kill DHCP again so I guess this is a mystery for the ages. Thanks.
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