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My laptop is connected to a network where we have routers with filters. I can use nmap to scan alive hosts and I can see open ports (mostly port 80). But then, when I try to ping those hosts, I dont receive any data. Can anyone point out what the problem is?

Thanks in advance!

[edit]

BTW, I can ping my own computer (localhost/my IP address).

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closed as off topic by Jenny D, pauska, mulaz, Ward, petrus Apr 16 '13 at 11:40

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Welcome to ServerFault! This is a site for professional sysadmins/network admins. With all due respect, since you don't know the difference between ping/ICMP and TCP, and you're not the person in charge of those routers/filters, this question does not seem to match that specification. –  Jenny D Apr 16 '13 at 9:46

2 Answers 2

up vote 5 down vote accepted

Just because a server or computer has a port open, does not mean it will respond to ICMP packets. Many in fact are specifically configured to not do so.

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Those are not servers, those are just computers just like mine! I can ping my own computer and it's working! –  kevin Apr 16 '13 at 8:43
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Computers have firewalls also nowadays. –  NickW Apr 16 '13 at 8:44
    
Windows 8 for example will not respond to pings by default: sysprobs.com/… –  NickW Apr 16 '13 at 8:45
    
I can see the webpage hosted by my friend (using Ubuntu) in my network from my computer, but I can't ping him. In that case, firewall allows me to send request to his port 80, right? (Please, correct me if im wrong) –  kevin Apr 16 '13 at 8:48
    
That's correct. His firewall drops ICMP packets, but allows TCP packets to port 80. –  NickW Apr 16 '13 at 8:50

Those hosts can have Windows Firewall service up and running.

You should check firewall rules on those host and verify if they allow icmp protocol.

You can read about icmp protocol here

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