Hi all

I have a seirra 4g mobile hotspot which I use to access the internet at home. I have it tethered to my pc via USB. It works fine, I can bring the interface (named wwan0) up manually no dramas. But for some reason it wont come up at boot properly. I say properly becuase when I boot, I cant access the internet but when I sudo ifup wwan0 it says the interface is already configured, so I have to ifdown wwan0 && ifup wwan0 Its not a huge problem but still annoying, but more annoying that I cant figure out why its doing it!

Details:

I have uninstalled network manager. Network Manager failed to recognise wwan0 and Im more comfortable just configuring /etc/network/interfaces
Im using Ubuntu 13.04. I was using Ubuntu Quantal Server(or maybe it might have been Precise... Think it quantal) on the same PC with the same setup and wwan0 always started properly on boot...
My /etc/network/interfaces reads:
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
address 192.168.1.2
netmask 255.255.255.0

auto wwan0
iface wwan0 inet dhcp
pre-up /etc/network/firewall
dns-nameservers 8.8.8.8 8.8.4.4

My firewall reads:
#load modules
modprobe ip_tables
modprobe iptable_nat
modprobe iptable_filter
#clear Rules
iptables -F
iptables -X
#Defualt filter chain actions:
iptables -P INPUT DROP
iptables -P OUTPUT ACCEPT
iptables -P FORWARD DROP
# Input Rules
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -i wwan0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -s 192.168.1.0/24 -j ACCEPT
#Forward rules
iptables -A FORWARD -i wwan0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth0 -o wwan0 -j ACCEPT
# clear NAT rules
iptables -t nat -F
iptables -t nat -X
# NAT
iptables -t nat -A POSTROUTING -o wwan0 -j MASQUERADE

(I use the PC as a gateway for my other devices)
Let me know if theres any other info I should give.

Thanks