Able to Ping Pc to ISP, but can't connect to internet. Help needed!

[Lechanna]

Hi all, 

I'm doing a lab for my networking class and I'm having trouble connecting to the ISP through PC1. The configuration is very basic. I have PC1 connected to Router1 which is then connected to the ISP. I do not have physical access to the ISP but I can at the very least connect to it with a cable. With the current running-config, R1 is able to ping the ISP and PC1. PC1 is also able to ping DNS, R1, and the ISP. I checked and the firewall is also disabled. Despite this, I am unable to connect to the internet. I have attached my running config as well as NAT translations for any sort of help!

Additionally, here is the information provided for me regarding the ISP's default gateway and DNS: 

Subnet Mask: 255.255.240.0

Default Gateway: 172.16.160.1

DNS1: 172.16.160.102

My Assigned “ISP” Internet Address Range: 172.16.161.10-255

[balaji.bandi]

just want to small tweak and test it :

remove below lines with no

no ip nat pool Test 172.16.161.10 172.16.161.255 netmask 255.255.240.0
ip nat inside source list 35 interface GigabitEthernet0/0/0 overload
ip route 172.16.160.0 255.255.240.0 172.16.160.1
!
!
access-list 35 permit 10.35.5.0 0.0.0.255 ( as per the interface config you using 255.255.255.128 , here you using /24) either change at Interface config to :

interface GigabitEthernet0/0/1
description R1 to PC1
ip address 10.35.5.1 255.255.255.0
ip nat inside
negotiation auto

or 

no access-list 35 permit 10.35.5.0 0.0.0.255

access-list 35 permit 10.35.5.0 0.0.0.127

try ping from PC to 8.8.8.8 and make sure PC has DNS lookup to work internet

still having issue post show run, show IP route

[Lechanna]

Hi, I tried what you recommended and it still does not work unfortunately. Here is the new running config and show route:

Router#show run

Building configuration...

Current configuration : 912 bytes

!

version 16.6.4

no service timestamps log datetime msec

no service timestamps debug datetime msec

no service password-encryption

!

hostname Router

!

!

!

!

!

!

!

!

ip cef

no ipv6 cef

!

!

!

!

!

!

!

!

!

!

!

!

spanning-tree mode pvst

!

!

!

!

!

!

interface GigabitEthernet0/0/0

description R1 to ISP

ip address 172.16.161.10 255.255.240.0

ip nat outside

duplex auto

speed auto

!

interface GigabitEthernet0/0/1

description R1 to PC1

ip address 10.35.5.1 255.255.255.128

ip nat inside

duplex auto

speed auto

!

interface GigabitEthernet0/0/2

no ip address

duplex auto

speed auto

shutdown

!

interface Vlan1

no ip address

shutdown

!

ip nat inside source list 35 interface GigabitEthernet0/0/0 overload

ip classless

ip route 172.16.160.0 255.255.240.0 172.16.160.1

!

ip flow-export version 9

!

!

access-list 35 permit 10.35.5.0 0.0.0.127

!

!

!

!

!

line con 0

!

line aux 0

!

line vty 0 4

login

!

!

!

end

Router# show ip route

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR

P - periodic downloaded static route

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C 10.35.5.0/25 is directly connected, GigabitEthernet0/0/1

L 10.35.5.1/32 is directly connected, GigabitEthernet0/0/1

172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

C 172.16.160.0/20 is directly connected, GigabitEthernet0/0/0

L 172.16.161.10/32 is directly connected, GigabitEthernet0/0/0

[Georg Pauwen]

Hello,

make these changes to your configuration. You currently have no routing:

--> no ip route 172.16.160.0 255.255.240.0 172.16.160.1
--> ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/0/0

[Lechanna]

Hi. I implemented the change you recommended. I tried to ping 8.8.8.8 from my pc and instead of a "destination host unreachable" error before implementing your change, I am now getting a "Request timed out" error.

[Richard Burts · Accepted solution]

I agree with Georg that not having a default route was a major issue. One consideration about his suggested default route is that if you configure a static route which specifies the outbound interface but not a next hop is that it requires your router to arp for every remote destination. And for that to work the upstream ISP device must support proxy arp. I wonder if your ISP does support proxy arp. As a test you can try this:

- from the PC attempt to ping 8.8.8.8

- after you get the error message on the router do show arp and post the output

It might be helpful to see the results of tracert (or other appropriate command depending on OS) to 8.8.8.8.

You might change the default route to this and see if it works any better

ip route 0.0.0.0 0.0.0.0 172.16.160.1

[Lechanna]

Hi Richard, I ended up changing the ip route to what you recommended and it ended up working! I am now able to connect to the internet. In summary, I ended up using the following commands to help me connect to the internet: 
no ip nat pool Test 172.16.161.10 172.16.161.255 netmask 255.255.240.0

no ip route 172.16.160.0 255.255.240.0 172.16.160.1
ip route 0.0.0.0 0.0.0.0 172.16.160.1 

Thank you all for the help!

[Richard Burts]

Thanks for the update. Glad to know that you have it working now. I am glad that our suggestions have been helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

[balaji.bandi]

Gateway of last resort is not set <<-- you do not have any route to go out.

My Assigned “ISP” Internet Address Range: 172.16.161.10-255   <---this need clarification, if the ISP give this range, then should be /24 not /20 i am in guess (this required some clarification).

on your orginal post - R1 is able to ping the ISP and PC1. PC1 is also able to ping DNS, R1, and the ISP.  <-- this mean from the begining you are not able to ping 8.8.8.8 from router it self.

Lets start with small tweak here  on your config.

interface GigabitEthernet0/0/0
description R1 to ISP
ip address 172.16.161.10 255.255.255.0  < this required some clarity
ip nat outside
duplex auto
speed auto

!
no ip route 172.16.160.0 255.255.240.0 172.16.160.1
ip route 0.0.0.0 0.0.0.0 172.16.161.1   ( i am thinking this is the correct gateway ) - but you need to confirm

Once you made this config, From Router do the below test and post here .

ping  172.16.161.1  (is this works ?)

ping 8.8.8.8 (is this works ? then do test from PC)

show ip arp

show ip route

show nat trans

from PC

ping 172.16.161.10 (is this works ?)

ping 172.16.161.1 (is this works ?)

ping 8.8.8.8 (is this works ?)

post from pc ipconfig /all (output text not screenshot)