asked on 7/27/2021

Cisco router can reach internet but attached switch and PC can not.

We are trying to setup some lab kit in the office real physical kit i've used packet tracer to draw out it thought, we have a Cisco router Int 0/0 which is getting an IP address via DHCP from our internet router 192.168.1.81 this is set as the outside interface for NAT. Then Int 0/1 has a static IP on 192.168.10.254 this is set as the inside interface for NAT. If I ping 8.8.8.8 from the router using source address 192.168.10.254 (Inside interface) the ping works fine.

We thought at first it was a routing problem, but if that was the case how would the router be able to reach the internet.

The Nat is working as I can see the translations

PC & Int Vlan 1 on the switch can both ping 192.168.1.81 (Outside interface) but can not reach 8.8.8.8

interface FastEthernet0/0
  ip address dhcp
  ip nat outside
  duplex auto
  speed auto

interface FastEthernet0/1
  ip address 192.168.10.254 255.255.255.0
  ip nat inside
  duplex auto
  speed auto

ip nat inside source list 1 interface FastEthernet0/0 overload
!
access-list 1 permit 192.168.10.0 0.0.0.255

IT_Router#ping 8.8.8.8 source 192.168.10.254

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 8.8.8.8, timeout is 2 seconds:
Packet sent with a source address of 192.168.10.254
!!!!!

IT_Router#show ip nat translations
Pro Inside global Inside local Outside local Outside global
icmp 192.168.1.81:29 192.168.10.254:29 8.8.8.8:29 8.8.8.8:29
icmp 192.168.1.81:30 192.168.10.254:30 8.8.8.8:30 8.8.8.8:30

Cisco Networking PC

Last Comment

Benjamin Van Ditmars

7/27/2021

ASKER CERTIFIED SOLUTION

Benjamin Van Ditmars

7/27/2021

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Ian Price

7/27/2021

ASKER

Yep we've put a default route in
C 192.168.10.0/24 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
S* 0.0.0.0/0 [254/0] via 192.168.1.1

We've not checked the router back from 192.168.1.1 - We presumed it's fine becasue the router can get in and out.

Mohammad Rummaneh

7/27/2021

all configuration seems fine but you need to check router back from 192.168.1.1

try to ping192.168.1.1 from PC , if it is working or not

Benjamin Van Ditmars

7/27/2021

if you perform nat, the route back doesnt have to be there. i can remember something with the outside interface on dhcp and a static route. normaly he has to receive its static route with dhcp.

can you give the router a static ip on the fast 0/0 to test this

and what you can test is ip route 0.0.0.0 0.0.0.0 interface fast 0/0