Add more notes

networking.md

@@ -21,4 +21,32 @@ ip link set dev eth5 up
 ip link set dev eth6 up
 ip link set dev eth7 up
 ip link set dev bond0 up
-```
+```
+
+## Troubleshooting
+
+### Packetloss
+
+* This kind of fast ping need to be applied only on ethernet links with MTU 1500. No packetloss should be present.
+```
+ping -c 1000 -i 0.01 -s1472 127.0.0.1
+ping -c 1000 -i 0.01 -s1472 nearby.ip
+```
+
+* Check if any dropped counter are increasing
+```
+tc -s -d qdisc show
+```
+
+* Check SFP signal level (if SFP supports DDM/DOM)
+```
+ethtool -m eth4
+```
+
+You might need to tune icmp rate limit if too many people ping this host:
+```
+net.ipv4.icmp_msgs_per_sec = 10000
+net.ipv4.icmp_ratelimit = 100000
+net.ipv4.icmp_msgs_burst=1000
+```
+