We are still on the same LAB scenario. We are going to work into different cases to do troubleshooting. Let’s start with case 1.
You got an issue that PCs in your LAN aren’t able to go to the internet.
Let’s login to the router and see what the issue is.
I will ping 1st from my Router to the ISP router interface which is my gateway. In my case, the ISP router’s interface which is connected to me is: 192.168.23.1/24 (normally the ISP should tell you what your gateway IP address)
I can see that I can reach that IP. Let’s try now to ping after that gateway IP, that means an IP on the internet. I will ping to 22.214.171.124:
Aha!!!! I see “no route to host” from the ping to 126.96.36.199
This clearly tells me that the problem is on the route. Let’s check if my router has still the default route on his routing table:
Ooopssss!!! The default route is missing. Looks like some engineer has played with the config. To get the default route back, I have to go to the DHCP client again and enable it from there. The other way is to add it manually, but for this LAB I will enable it from the DHCP client.
Let’s first check if it is disabled on the DHCP client:
Indeed. It is disabled. I will enable it now.
Let’s check if I have received the default route again on the router:
Here it is.
Now the problem should be solved. I will ping from my router again to 188.8.131.52:
Now the ping is working, and the LAN PCs are able to go to the internet.
A Junior engineer has contact you saying that the Router can ping to 184.108.40.206 but cannot ping to google.com. He is asking for your assistance on this.
If the router is able to ping to 220.127.116.11 that means the connectivity to the internet is working. The problem is only when pinging to the domain names like google.com. For me, this means that the DNS is not functioning on the router.
Let’s check if the router has a DNS set on it:
Here I can see clearly that the router didn’t receive DNS addresses automatically from the ISP, also there is no any DNS address set manually on the router.
In this case, we can solve the problem by setting up DNS address(es) manually on the router, or we enable it from the DHCP client. I will use the 2nd method. But 1st let me check if the “Use Peer DNS” is disabled on the DHCP client:
Indeed. Someone has disabled it.
I will enable it now then check if I have received the DNS addresses automatically.
This has been enabled. Let’s check if I have received the DNS addresses on the router.
Indeed, they have been received.
I will ping now to google.com from my router and see the result.
It is working now. So, we have solved the problem of this case.
You have received a call from one of your colleagues saying that his PC can ping to the gateway 192.168.88.1 but not to the internet. You have checked the configuration on the router, and everything looks working well. So, you have concluded that the problem is on the PC itself.
If he is able to ping to his gateway, that means the Layer 3 connectivity is working. So here you assume that the problem could be from the gateway which is set to his PC.
Let’s check his TCP/IP settings on his PC:
Look at that. His gateway has a wrong IP, that’s why he cannot go to the internet. The gateway IP should be 192.168.88.1
Let’s change it and see if the internet will work on his PC.
The Gateway has been successfully changed. Let’s ping to google.com now from the PC:
Here we go!!! We solved the problem, and we asked our colleague to never play with the TCP/IP settings anymore ????
You have received a call from one of your colleagues saying that his PC can ping to 18.104.22.168 but not able to open any website. As the PC is able to reach 22.214.171.124, that means all configuration on the router is correct and the PC is also connected to the internet, but the problem is to reach to domain names. So, you have concluded that the problem is on the DNS address of the PC.
Let’s check if we can ping to 126.96.36.199:
It is working.
Let’s try to ping google.com:
It is not working.
The problem is surely the DNS addresses that are set on the PC. Let’s check that:
Look at this. Someone has changed the DNS addresses to wrong ones. Those addresses are not DNS addresses. I will change them to 188.8.131.52 and 184.108.40.206:
Let’s try now to ping google.com to see if the DNS would make the mapping between the domain name and IP address:
Now it is working ????
That’s all what I wanted to show you in this chapter, I hope you have enjoyed it and see you in the upcoming one.