How come I can ping google but not a PC on a different subnet within my campus network?

Question

I am a newbie to the networking world. I know that one cannot ping two PCs connected to different subnets unless you have a router in between.

But, I was wondering how come I can ping www.google.com but not a PC on a different subnet within my campus? Obviously, the google server which I am pinging and my PC are not on the same subnet.

Can someone please help me clarify my concepts.

Thanks.

Answer 1

There's a couple of different reasons why this could be:

• The computer you are trying to ping doesn't respond to ping.
• If you are using a host-name, the target's host-name won't be in DNS.
• The router serving your target subnet isn't routing pings.
• There is a firewall blocking ICMP (ping protocol) traffic.

You will always have a (at least one) "router in between" and google's server is a "computer on another subnet", but both the 'router', and the 'computer' both have to opt-in to servicing ping requests.

Answer 2

Most of todays computers, that are connected to the Internet, are protected by a firewall. In many instances, this firewall is configured to "drop" (i.e. ignore) incoming pings (echo-request messages of the ICMP protocol). This ofcourse stops the target of your ping from answering.

In addition to that, some network administrators even go as far as discarding echo requests on the perimeter, i.e. at the router, where the Internet connection is fed into the site network.

Answer 3

Presuming you are using the correct terminology of subnet then this is because of NAT, it appears as though your network administrators have set the networks NAT to be able to communicate with the internet however not other subnet's within the LAN, quite common as to do so would mean an extra NAT rule.

Otherwise it may be the case of your friends computer's firewall is set to not reply to incoming pings (ICMP Protocol) or even the network administrator has set to discard ICMP packets on your network for security reasons.