Cisco 1841: Can ping ip addresses but cannot connect to the Internet

[davidkagimba]

Hi,

I have recently changed ISP and had to configure my router to accomodate the new ISP. But for some reason I cannot seem to connect to the Internet.

My setup consists of the ISP's modem, my router and then a bunch of switches for the LAN.

With the old ISP, the config was as follows:

Interface FastEthernet 0/0

Description LAN Interface

ip address 192.168.5.1 255.255.255.0

ip nat inside

Interface Serial 0/0/0

Description ISP INTERNET LINK

ip address 10.88.96.212 255.255.255.252

ip nat outside

ip name-server 123.108.252.50

ip name-server 123.108.252.51

ip route 0.0.0.0 0.0.0.0 10.88.96.212

ip nat inside source list 1 interface serial 0/0/0 overload

access-list 1 permit 192.168.0.0 0.0.0.255

access-list 1 permit 192.168.5.0 0.0.0.255

Everything worked fine. With the new ISP, the cable modem they provided has one ethernet port which I connect to one of my FastEthernet ports.

I setup the router for the new ISP like so:

Interface FastEthernet 0/0

Description CRS LAN Interface

ip address 192.168.5.1 255.255.255.0

ip nat inside

Interface FastEthernet 0/1

Description ISP INTERNET LINK

ip address 192.167.18.222 255.255.255.252

ip nat outside

ip name-server 51.202.229.132

ip name-server 51.202.229.130

ip route 0.0.0.0 0.0.0.0 192.167.18.221

ip nat inside source list 1 interface FastEthernet 0/1 overload

access-list 1 permit 192.168.0.0 0.0.0.255

access-list 1 permit 192.168.5.0 0.0.0.255

From my router, I can ping the gateway 192.167.18.221. I can ping all devices in my LAN but I cannot connect to the Internet.

If I connect the ISP modem via ethernet cable directly to my laptop, the Internet works so there seems to be a problem with my config.

Would like some assistance. Thanks in advance

[aftabsiddiqui]

have you checked the NAT translation if its working?

[davidkagimba]

Will do when I get a chance. I have a feeling I messed up the NAT config

[prajithtr_2]

What is subnet mask you gave to the laptop's ip address?

[davidkagimba]

Computers in the LAN are all on 255.255.255.0. I am using dhcp via windows server

If you mean for a direct connection from modem to laptop then:

255.255.255.252 (the isp's mask)

[mfurnival]

Turn on NAT debugging "debug ip nat" and ping as follows:

ping 8.8.8.8 source fa0/0

and post the results. Don't forget to turn on "term mon" is you are not connected via console.

[Richard Burts]

When you connect your laptop to the provider modem is the laptop using DHCP or did you manually set the address?

You tell us that the router is able to ping the next hop gateway. I wonder if the router is able to ping anything beyond that? And are you pinging using names for the destination or using IP addresses of the destination?

HTH

Rick

[davidkagimba]

I set the address manually when connected from laptop to modem.

I am pinging using IP addresses

[John Blakley]

David,

Rick asked a good question that I didn't see an answer for. Can you ping anything outside of their modem? You have said that you can ping the default gateway from your router, which would be the ISP's router, but can you, from your Cisco, ping 8.8.8.8 or 8.8.4.4? If you can, try removing "ip nat outside" and "ip nat inside" from the router and then put them back on. I'm wondering if the nat translation table wasn't automatically rebuilt after changing the address on the router.

HTH,
John

*** Please rate all useful posts ***

[davidkagimba]

Yes I can ping 8.8.8.8 and 8.8.4.4 from my router.

I have removed ip nat outside and ip nat inside from the rotuer and put them back in but nothing changed. Still unable to connect to the internet.

Unless I did it wrong. To remove, I entered the specific interface and typed 'no ip nat inside'

i.e

int fa0/0

no ip nat inside

exit

int fa0/1

no ip nat outside

exit

[John Blakley]

Okay, let's do this. Can you run "debug ip nat" and then "ping 8.8.8.8 source fa0/0" and then post the results? Also post "sh ip nat trans".

HTH,
John

*** Please rate all useful posts ***

[davidkagimba]

debug ip nat

-------

*Feb 1 07:12:46.959: NAT: expiring 10.88.96.212 (192.168.5.8) udp 6100 (6100)

*Feb  1 07:12:51.055: NAT: expiring 10.88.96.212 (192.168.5.8) udp 6101 (6101)

*Feb  1 07:12:46.959: NAT: expiring 10.88.96.212 (192.168.5.8) udp 6102 (6102)

*Feb  1 07:12:58.735: NAT: expiring 10.88.96.212 (192.168.5.8) udp 6103 (6103)

*Feb  1 07:13:02.831: NAT: expiring 10.88.96.212 (192.168.5.8) udp 6104 (6104)

*Feb  1 07:13:06.927: NAT: expiring 10.88.96.212 (192.168.5.8) udp 6105 (6105

*Feb  1 07:13:24.847: NAT: expiring 10.88.96.212 (192.168.5.8) udp 6106 (6106)

*Feb  1 07:15:59.831: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [23311]

*Feb  1 07:16:00.307: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [590]

*Feb  1 07:16:39.915: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [23516]

*Feb  1 07:16:39.915: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [23517]

*Feb  1 07:16:39.919: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [23518]

*Feb  1 07:16:39.919: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [23519]

*Feb  1 07:16:40.183: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [15730]

*Feb  1 07:16:40.191: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [15735]

*Feb  1 07:16:40.911: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [16027]

*Feb  1 07:16:40.911: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [16028]

*Feb  1 07:16:40.915: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [23527]

*Feb  1 07:16:40.915: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [16029]

*Feb  1 07:16:40.919: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [16030]

*Feb  1 07:16:40.923: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [23528]

*Feb  1 07:20:00.951: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [24439]

*Feb  1 07:20:01.415: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [21093]

*Feb  1 07:20:36.331: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [7563]

*Feb  1 07:20:36.335: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [7564]

*Feb  1 07:20:36.335: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [24598]

*Feb  1 07:20:36.335: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [24599]

*Feb  1 07:20:36.799: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [8363]

*Feb  1 07:21:39.979: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [25017]

*Feb  1 07:21:39.979: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [25018]

*Feb  1 07:21:40.247: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [34]

*Feb  1 07:21:40.251: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [35]

*Feb  1 07:21:40.727: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [25023]

*Feb  1 07:21:40.995: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [257]

*Feb  1 07:21:40.995: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [25026]

*Feb  1 07:21:41.263: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [322]

*Feb  1 07:21:41.691: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [482]

*Feb  1 07:21:41.691: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [483]

*Feb  1 07:21:41.691: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [484]

*Feb  1 07:21:41.691: NAT*: s=132.245.1.25, d=10.88.96.212->192.168.5.10 [485]

*Feb  1 07:21:41.695: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [25028]

*Feb  1 07:21:41.695: NAT*: s=192.168.5.10->10.88.96.212, d=132.245.1.25 [25029]

ping 8.8.8.8 source fa0/0

-------

Sending 5, 100-byte ICMP Echos to 8.8.8.8, timeout is 2 seconds:

Packet sent with a source address of 192.168.5.1

!!!!!

Success rate is 0 percent (0/5)

--------

sh ip nat trans

-------

Pro Inside global          Inside local               Outside local          Outside global

tcp 192.167.18.222:2020          192.168.5.10:2020          132.245.1.25          132.245.1.24:443

-------

sh ip route

-------

Gateway of last resort is 192.167.18.221 to network 0.0.0.0

C          192.168.5.0/24 is directly connected, FastEthernet0/0

                192.167.18.0/30 is subnetted, 1 subnets

C          192.167.18.220 is directly connected, FastEthernet 0/1

S*         0.0.0.0/0 [1/0] via 192.167.18.221

-------

sh run | s nat

-------

ip nat inside

ip nat outside

ip nat outside

ip nat inside

ip nat inside source list 1 interface FastEthernet0/1 overload

Edit: typo in the debug part... 10.88.96.212 should be 192.167.18.222

[John Blakley · Accepted solution]

David,

Can you ping 8.8.8.8 from a workstation? If so, it's dns related. You can test this by taking out the two name servers in your router and adding 8.8.8.8. After that, try to ping www.google.com sourcing from fa0/0. If you get a response, your natting/internet is working. Then put the same config (dns entries) on a workstation. Try to ping google from there. If that works, you're good.

HTH,
John

*** Please rate all useful posts ***

[davidkagimba]

Oh man, turns out it was a dns issue like you and satya said.

I changed the name-servers in the router (to 8.8.8.8 and 4.4.4.4) and on my Laptop and the Internet WORKS!!!!

Which made me realise that I hadn't changed the forwarders on my DNS Servers in my LAN. So I changed the forwarders (on my DNS Server) to the ISP DNS IPs and now I can use the ISP name-servers in the router.

You guys have all been so awesome. In just these few days I have learnt so much. Everyone has been so helpful. Great community here

Thanks a lot

[cadet alain]

Hi,

in addition to John request could you also post sh ip route output as well as sh run | s nat

Regards

Alain

Don't forget to rate helpful posts.