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Top Forums UNIX for Beginners Questions & Answers Can ping out but cannot receive Post 303021955 by rbatte1 on Tuesday 21st of August 2018 12:28:33 PM
Old 08-21-2018
You are proving that you can lookup the DNS name to give you an IP address and indeed you may be sending packets and requests out from your server, but zero packets received means:-
  • The target IP is not active
  • There is no route to the target IP (you mention google.com but then a 172.x.x.x private address)
  • Your outbound IP tables may filter them out
  • Your network devices may filter them out
  • The target IP may ignore you
  • The target IP may try to respond but your public-facing proxy may filter them out
  • The target IP may try to respond but your internal network devices may filter them out
  • The target IP may try to respond but your inbound IP tables may filter them out

A ping is one type of packet, so it does not guarantee that you will actually be able to hold a conversation with the target address.


What is your eventual intention for which I presume that this is a step? Perhaps there is a better way to be monitoring what it is that you really need.



Kind regards,
Robin
 

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Firewall mark classifier in tc(8)				       Linux					 Firewall mark classifier in tc(8)

NAME
fw - fwmark traffic control filter SYNOPSIS
tc filter ... fw [ classid CLASSID ] [ action ACTION_SPEC ] DESCRIPTION
the fw filter allows to classify packets based on a previously set fwmark by iptables. If it is identical to the filter's handle, the fil- ter matches. iptables allows to mark single packets with the MARK target, or whole connections using CONNMARK. The benefit of using this filter instead of doing the heavy-lifting with tc itself is that on one hand it might be convenient to keep packet filtering and classifi- cation in one place, possibly having to match a packet just once, and on the other users familiar with iptables but not tc will have a less hard time adding QoS to their setups. OPTIONS
classid CLASSID Push matching packets to the class identified by CLASSID. action ACTION_SPEC Apply an action from the generic actions framework on matching packets. EXAMPLES
Take e.g. the following tc filter statement: tc filter add ... handle 6 fw classid 1:1 will match if the packet's fwmark value is 6. This is a sample iptables statement marking packets coming in on eth0: iptables -t mangle -A PREROUTING -i eth0 -j MARK --set-mark 6 SEE ALSO
tc(8), iptables(8), iptables-extensions(8) iproute2 21 Oct 2015 Firewall mark classifier in tc(8)
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