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I'm wondering if anyone has ideas on this one, since it's a first for me. I can access the internet just fine with a browser, but using PING or TRACERT from a command prompt just shows requests timing out once they leave my network.

To take some variables out of the equation, I tried reducing my network infrastructure down to just the Comcast cable line coming out of the wall connected to a Linksys BEFCMU10 v4 cable modem which went directly to my Windows 7 laptop with no software firewall, and the issue was still present.

Again, I'm browsing the internet (like posting this question) just fine, but can't ping anything (including this site right now) without all the packets getting lost.

I'm not blocking ICMP on my side, and I don't suspect Comcast is systematically blocking it all the sudden. What am I overlooking?

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The backstory for this is that I was having some VPN issues, so I started by seeing if I could ping the VPN server, but then found out I couldn't ping anything and get results. –  sXe Sep 30 '11 at 21:09

3 Answers 3

A lot of sites may choose to turn off ping response for security reasons, but are still accessible through the limited number of ports that are opened (like 80 for http and 443 for https). Here's some documentation for Linux: http://www.linuxhowtos.org/Security/disable_ping.htm

So in summary, being unable to ping something doesn't mean that you have network issues.

Hope this helps!

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I was thinking that at first, but in this case I can't ping any site, including yahoo.com and google.com as well as domains that I own and know I've pinged in the past and haven't changed settings since. They resolve to their IP address correctly but the requests timeout regardless of buffer size and setting a longer timeout window--even though accessing them through a browser works lightning fast. I'm still stumped, but I don't think it's related to any specific site. I'm not sure whether or not it's indicative of a network issue, but ultimately it's something I'd like to understand better. –  sXe Sep 30 '11 at 21:40
    
@sXe, can you ping your router/gateway? At minimum, you should be able to do that. With other machines/servers, "pingablility" is outside of a user's control. This SU post might also be handy: superuser.com/questions/217285/… –  JW8 Sep 30 '11 at 22:37
    
there's no problem pinging inside my network. I can ping my modem directly, and when I'm in my normal network configuration (ie, a router between me and the modem) I can ping that too. When I do a tracert out to a website, it will resolve to my router just fine and everything times out after it leaves the network. So no problem with the ping utility itself or connectivity within the network--I can reach the other devices on my network just fine, and like I said I can connect browse the internet no problem. –  sXe Oct 1 '11 at 0:16
up vote 2 down vote accepted

It turned out to be the cable modem at fault, and a hard reset of that component seems to have straightened it out. In retrospect, since I removed every component of my network except the cable modem and a single laptop to simplify the test, it probably should have been more obvious at the time that it was the culprit.

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Your router can filter ICMP-packets from external world. If you can login to router and try to ping from it's shell it can give you some hints

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Yeah, that was my first thought which is why I took the router out of the loop and confirmed that I was getting the same behavior without having it between my workstation and my internet connection. But for thoroughness sake, I did the ping test straight from my router's diagnostic interface and still got 100% packet loss... –  sXe Oct 2 '11 at 1:06
    
If you can ping modem (different from router device) it means what it also in router, not bridge mode. So- my idea is applicable to it also –  Lazy Badger Oct 2 '11 at 1:15

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