Cisco UBr and DHCP Prob

Hello, everyone.
I'm wondering if the subject is possible. I have a cisco router and a linux server with dhcpd several hops away. Cisco is relaying dhcp requests from the devices to a linux server through a GRE tunnel. I'm getting the REQUEST dhcp packets on a tunnel interface (checked with tcpdump). However the dhcp log is empty. UBR config is as follows. I can ping the Cable1/0 interface(s) from the dhcp server (Centos). I can not ping the public ip address of the dhcp server from the Cable1/0 interface though.

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Current configuration : 4492 bytes
!
! Last configuration change at 19:49:00 EST Thu Dec 24 2009
! NVRAM config last updated at 17:05:35 EST Wed Dec 23 2009
!
version 12.3
service timestamps debug datetime
service timestamps log datetime
service password-encryption
!
hostname Merrillville.Lakes
!
boot-start-marker
boot-end-marker
!
enable secret 5
!
clock timezone EST -5
clock summer-time EDT recurring
cable admission-control preempt priority-voice
cable modem remote-query 120 public
no cable qos permission create
no cable qos permission update
cable qos permission modems
no aaa new-model
ip subnet-zero
!
!
ip cef
no ip domain lookup
ip dhcp relay information option
!
!
!
!
!
!
!
!
interface Tunnel0
description DHCP
ip address 16.16.16.2 255.255.255.252
tunnel source 76.77.XXX.XX
tunnel destination 69.3.XXX.XX
!
interface Tunnel1
description TFTP
ip address 17.17.17.5 255.255.255.252
tunnel source 76.77.XXX.XX
tunnel destination 69.3.XXX.XX
!
interface Tunnel2
description --== Mario ==-
ip address 18.18.18.1 255.255.255.252
tunnel source 76.77.XXX.XX
tunnel destination 69.3.XXX.XX
!
interface FastEthernet0/0
ip address 76.77.XXX.XX 255.255.255.252
duplex full
speed auto
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Cable1/0
ip address 10.0.50.1 255.255.254.0 secondary
ip address 10.0.10.1 255.255.254.0
ip access-group 150 in
ip access-group 150 out
ip nat inside
no cable packet-cache
cable downstream channel-id 0
cable downstream annex B
cable downstream modulation 64qam
cable downstream interleave-depth 32
cable downstream frequency 561000000
no cable downstream rf-shutdown
cable downstream rf-power 51
cable upstream 0 frequency 38000000
cable upstream 0 docsis-mode tdma
cable upstream 0 channel-width 1600000
cable upstream 0 minislot-size 4
cable upstream 0 power-level 0
cable upstream 0 modulation-profile 1
no cable upstream 0 shutdown
cable arp filter request-send 3 2
cable arp filter reply-accept 3 2
no cable arp
cable dhcp-giaddr policy
cable helper-address 69.3.XXX.XX
no keepalive
!
ip nat translation timeout 300
ip nat translation tcp-timeout 300
ip nat translation udp-timeout 20
ip nat translation syn-timeout 300
ip nat translation dns-timeout 20
ip nat translation icmp-timeout 20
ip nat translation max-entries 6500
ip nat pool Merrillville.Lakes_CPE 76.77.XXX.XX 76.77.XXX.XX netmask 255.255.255.248
ip nat inside source list 105 pool