VLANs unable to reach outside world

Question

I just purchased a Cisco 1941 ISR for my home lab and I'm running into a problem with getting all my devices behind it to get to the internet. Below is a layout of my network.
I have 7 VLANs on an SG300-20 layer 3 switch. The switch is connected to my 1941 ISR. I have cable and my ISP is Comcast and they provide a cable modem/router as well. Unfortunately I cannot get rid of this device and I cannot turn off the routing functionality, however I don't actually think that this devices itself is causing any problems with the way I have it setup. I have a block of 5 static IP's from my ISP. I've used one of them as the IP address of my WAN link (G0/1), while the other interface is connected to my LAN (G0/0).
I have interVLAN networking working just fine. I'm able to ping any VLAN gateway and/or host from any other device (this includes my switch and ISR). From my switch or any device behind it, I can ping the switch (10.1.8.1), I can ping my router (10.1.8.2), and I can even ping my router's WAN link (75.148.101.25). However, I cannot ping comcast's router (75.148.101.30). What is weird is that I can ssh into my ISR (which I can do from any device) and the Cisco router can ping the Comcast router and the outside world.
If I try to ping 75.138.101.30 (Comcast external IP) from my switch or any device behind it, I get no response. If I try to ping 75.138.101.30 (Comcast external IP) from the Cisco 1941 I get a response.
To me this looks like a problem with the Cisco router. It knows where to forward traffic but is refusing to do so for anything that does not originate from the router itself.
Very lost at this point and looking for help.
Thanks,
Joshua

Answer 1

Sure, no problem, happy to provide the full config. I'm very new to networking and just getting started, what command do I need to run to show the nat access list
raynor#show running-config
Building configuration...
Current configuration : 1827 bytes
! Last configuration change at 23:18:53 UTC Sat Aug 16 2014 by jschaeffer
! NVRAM config last updated at 23:20:33 UTC Sat Aug 16 2014 by jschaeffer
version 15.1
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
hostname raynor
boot-start-marker
boot-end-marker
enable secret 5 $6$t7$FHadfus1vHhykVc2QolPwTz/
no aaa new-model
no ipv6 cef
ip source-route
ip cef
ip domain name harmonywave.com
ip name-server 75.75.75.75
ip name-server 75.75.75.76
multilink bundle-name authenticated
crypto pki token default removal timeout 0
license udi pid CISCO1941/K9 sn FGL172610ZP
username jschaeffer secret 5 $1$IQxQ$DtfZuO78mBeiEbsVD95Afq1
username ckrupa one-time secret 5 $1$HAnq$$faaybor7t7wqewOqFLm9u0
ip ssh version 2
interface GigabitEthernet0/0
 description WAN link
 ip address 75.148.101.25 255.255.255.248
 ip nat outside
 ip virtual-reassembly in
 no ip route-cache cef
 no ip route-cache
 duplex auto
 speed auto
 no cdp enable
interface GigabitEthernet0/1
 description LAN link
 ip address 10.1.8.2 255.255.255.0
 ip nat inside
 ip virtual-reassembly in
 no ip route-cache cef
 no ip route-cache
 duplex auto
 speed auto
 no cdp enable
ip forward-protocol nd
no ip http server
no ip http secure-server
ip route 0.0.0.0 0.0.0.0 75.148.101.30
ip route 10.1.10.0 255.255.255.224 10.1.8.1
ip route 10.1.10.32 255.255.255.224 10.1.8.1
ip route 10.1.10.64 255.255.255.192 10.1.8.1
ip route 10.1.11.0 255.255.255.0 10.1.8.1
ip route 10.1.12.0 255.255.255.0 10.1.8.1
ip route 10.1.15.0 255.255.255.0 10.1.8.1
no cdp run
control-plane
line con 0
 logging synchronous
line aux 0
line vty 0 4
 login local
 transport input ssh
line vty 5 15
 login local
 transport input ssh
scheduler allocate 20000 1000
end