Can't get DHCP to work..

[snootalope]

Hello

I'm trying to get my Cisco 1751-v router to assign DHCP address to 7940 phones. I can't for the life of me get this to work.

The phones are plugged into a PoIE 3500 Cisco Switch. The router is plugged into port 24 of the switch.

Switch IP: 172.16.3.254
Router sub IP: 172.16.3.1

The switches VLAN1 is configured with the 172.16.3.254.

From the switch I can ping 172.16.3.1 just fine. And vice versa.

On the router I've setup a DHCP pool with the network address 172.16.3.0 255.255.255.0

I turned on DHCP debugging on the router and can see this message:

Jun 21 05:00:27.999: DHCPD: DHCPDISCOVER received from client 0100.1b53.5c7a.d6 on interface FastEthernet0/0.3.
Jun 21 05:00:27.999: DHCPD: subnet [172.16.3.1,172.16.3.254] in address pool AZ is empty.

The MAC there is the single phone I'm testing... so the request is getting to the router but it's saying the pool is empty.

What am I missing here??

 

[burtsbees]

Post a config from the 1751.

Burt

 

[snootalope]

!
memory-size iomem 15
clock timezone PST -7
ip subnet-zero
!
!
no ip domain lookup
ip dhcp conflict logging
ip dhcp excluded-address 172.16.3.1 255.255.255.0
!
ip dhcp pool AZ
network 172.16.3.0 255.255.255.0
option 150 ip 172.16.3.1
!
ip cef
!
!
interface FastEthernet0/0
no ip address
speed auto
!
interface FastEthernet0/0.1
encapsulation dot1Q 1 native
ip address 10.10.3.1 255.255.255.0
ip helper-address 10.10.1.5
!
interface FastEthernet0/0.3
encapsulation dot1Q 3
ip address 172.16.3.1 255.255.255.0
!
interface Serial0/0
no ip address
encapsulation frame-relay
no ip mroute-cache
load-interval 30
shutdown
no fair-queue
frame-relay traffic-shaping
frame-relay ip rtp header-compression
h323-gateway voip interface
!
interface Serial0/0.16 point-to-point
description phoenix
ip address 172.1.1.4 255.255.255.252
no ip mroute-cache
frame-relay interface-dlci 16 CISCO
class qos-1536k
frame-relay ip tcp header-compression
frame-relay ip rtp header-compression
!
router bgp 19007
no synchronization
bgp log-neighbor-changes
no auto-summary
!
ip classless
no ip forward-protocol udp netbios-dgm
ip route 0.0.0.0 0.0.0.0 172.1.1.10
no ip http server
!
!
!
!
map-class frame-relay qos-1536k
frame-relay cir 1505280
frame-relay bc 188160
frame-relay be 0
frame-relay mincir 1505280
service-policy output qos
!
map-class frame-relay voip_768
frame-relay cir 768000
frame-relay bc 7680
frame-relay be 0
frame-relay mincir 768000
frame-relay fair-queue
frame-relay fragment 960
access-list 102 permit ip any host 172.16.1.1
access-list 102 permit ip any host 172.16.1.2
access-list 105 permit ip any 172.16.0.0 0.0.255.255 precedence critical
access-list 105 permit udp any 172.16.0.0 0.0.255.255 range 16384 32767
access-list 105 permit ip any 172.16.0.0 0.0.255.255 dscp ef
access-list 150 permit udp any eq 1719 any
access-list 150 permit udp any any eq 1719
access-list 150 permit tcp any eq 1720 any
access-list 150 permit tcp any any eq 1720
!
snmp-server community az RO
snmp-server enable traps tty
call rsvp-sync
!
voice-port 1/0
input gain -1
echo-cancel coverage 32
echo-cancel suppressor
no vad
no comfort-noise
timeouts interdigit 2
!
voice-port 1/1
input gain -1
echo-cancel coverage 32
echo-cancel suppressor
no vad
no comfort-noise
timeouts interdigit 2
!
!
mgcp profile default
!
dial-peer cor custom
!
!
!
dial-peer voice 91 pots
preference 1
destination-pattern 6T
!
dial-peer voice 92 pots
preference 2
destination-pattern 6T
!

 

[3wsparky]

wheres the dhcp server live if its the one on that config above then you need to remove the ip helper address as its pointing to another dhcp server

 

[burtsbees]

Remove this...
ip helper-address 10.10.1.5
Then you will see the phones get IP addresses in the 172.16.3.0/24 range. I know that it seems the IP phones would see the config in the router to get a dhcp address before the dhcp requests get to the helper address and that subnet, but the router processes all dhcp server info, and it won't know what to do with the requests..."Do I give it an IP address from my pool, or do I forward the dhcp request to the dhcp server at 10.10.1.5???
This is especially true since the fa0/0 interface has both the routers dhcp scope and the helper address configured on it, being a trunking interface for the VLANs.
The thing with dhcp and phones is that you first attach a laptop to the subnet where dhcp is configured...if it gets an IP address, but the phone does not, you know that the problem lies in the phone. If neither would get an IP address, you know the problem would be in the dhcp server.

Burt

 

[snootalope]

Thanks for the replies guys.

The problem was the subnet mask on the ip address in the dhcp pool.

ip address 172.16.3.1 255.255.255.0

changed to:

ip address 172.16.3.1

and that did the trick...

 

[burtsbees]

So you needed a /16 then?

Burt

 

[snootalope]

Sorry, I was wrong on my last reply.

The problem was the ip dhcp excluded-address! I had to remove the subnet mask from that.

ip dhcp excluded-address 172.16.3.1 255.255.255.0

Changed to:

ip dhcp excluded-address 172.16.3.1