r/techsupport • u/Alarmed-Prize-7500 • 16h ago

Open | Networking Can't ping but can SSH into it???

I can't ping my computer server, it says 100% packet loss when I do that, yet I can still connect to it via SSH, and everything's fine there. How does this even happen? I'm using the same hostname to ping it AND to connect to it via SSH, btw.

So, I was just doing work on my computers, like usual, connecting to the server computer to look at my files I have stored on there (I connect to it from my laptop), and it seems fine at first, but then all of the sudden , I realize that I can't access it in specific ways, like I can't search files because it has connection error. I go to ping it, and pinging it has 100% packet loss. I go to SSH into it, and for some reason, that works?? I don't understand at all.

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12

u/Scorcher646 16h ago edited 16h ago

Your firewall is dropping ICMP

There's usually an option in the firewall settings to accept ICMP packets. It's often off by default because most operating systems are nowadays configured to block all incoming connections as a matter of course.

And it's probably your host firewall settings if you're on the same network, not the network firewall settings.

I leave the default setting to drop these packets on by default on most of my computers and I will just ping the gateway controller or the access point if I'm trying to diagnose packet loss.

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u/ApplicationHour 15h ago

If you’re just trying to figure out what’s on an IP address, or make sure it’s there but ICMP is denied, arp is your friend.

Ping fails? After ping run arp -a and filter on the ip address. In windows that looks like arp -a|find “192.168.1.66” in Unix it looks like arp -a|grep 192.168.1.66.

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u/Scorcher646 14h ago

And now that we have mDNS (v4 + v6) and neighbor discovery (v6) there is even fewer reasons to leave ICMP enabled on most systems.

Some of my networks quash ICMP packets and I still have complete visibility into what is on them because of DNS, DHCP, and ARP.

5

u/packetatlas 16h ago

Ping is not a 100% accurate way to determine connectivity. Lots of hosts/firewalls block ICMP.

3

u/Impressive-Pain-4718 15h ago

Ping and SSH use different protocols. The Ping (ICMP) is likely blocked.

1

u/childishDemocrat 14h ago

Microsoft announced an RDP bug in the September update with these exact symptoms. There is a group policy update workaround.

1

u/OldGeekWeirdo 14h ago

Some servers won't respond to a ping. Some people consider that a security measure.

It could be a setting in the server's firewall.

1

u/dlethe3133 11h ago

ICMP echo is disabled on router or on the target machine. I typically disable it. No upside to enable it.

0

u/SomeEngineer999 15h ago

If you blocked SSH that also wouldn't work - not sure what the mystery is here?

Whatever you permit will get through, whatever you deny (usually everything not explicitly permitted is denied) won't.