[TriLUG] New CentOS 7 system headaches (ping & dnsmasq)

[Matt Flyer via TriLUG]

First thing I would do is try to nail it down to being a firewall
issue.
You said that firewalld is disabled.  Be sure to look at the active
process list to confirm.  Then set IPtables to accept by default and
flush it - to clear out everything and make it permissive and then see
if you can ping.

If you still can't ping, try running a traceroute, though it should be
one hop on the LAN segment, just to see if it is somehow trying to
route to the gateway.  

Also, double check your interfaces by pulling up an ifconfig in a
terminal prompt and verify that it didn't do anything odd like create
multiple gateways (I am assuming here you're running multiple LAN
segments on the same machine from your description) because sometimes
the auto configuration tools assume you have a simple setup. 

On Mon, 2016-12-19 at 16:22 -0500, Brian via TriLUG wrote:
>   Here's some salient info:
> 
> SELinux is disabled
> firewalld is disabled in favor of iptables-services (for the time
> being)
> 
> There is a rule to ACCEPT all inbound traffic from the private 
> (10.55.46.0/24) interface.  From iptables-save output:
> 
> 	-A INPUT -j my_firewall
> 	-A my_firewall -i enp7s0 -j ACCEPT
> 
> dnsmasq is running and listening.  From netstat output:
> 
> 	tcp 0 0 0.0.0.0:53 0.0.0.0:* LISTEN 3624/dnsmasq
>          udp 0 0 0.0.0.0:53 0.0.0.0:* 3624/dnsmasq
> 	udp 0 0 0.0.0.0:67 0.0.0.0:* 3624/dnsmasq
> 
> There is also a firewall rule allowing all ICMP packets.
> 
> 	-A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type any -j
> ACCEPT
> 
> Here are the symptoms:
> - I can't ping in or out on the internal interface:
> blueman$ ping 10.55.46.80
> PING 10.55.46.80 (10.55.46.80) 56(84) bytes of data.
> ^C
> --- 10.55.46.80 ping statistics ---
> 3 packets transmitted, 0 received, 100% packet loss, time 1999ms
> 
> undecidedgames$ ping 10.55.46.125
> PING 10.55.46.125 (10.55.46.125) 56(84) bytes of data.
> ^C
> --- 10.55.46.125 ping statistics ---
> 2 packets transmitted, 0 received, 100% packet loss, time 999ms
>