Lab 4, Exercise 4.1, disrepancy of the result

fliker09

In the solution (2) it is said, I quote:

"You should see all the requests being sent, but a smaller number of responses."

Actually, both requests and replies are getting dropped:

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode

listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes

11:15:38.737856 IP localhost > localhost: ICMP echo request, id 5064, seq 1, length 64

11:15:38.737921 IP localhost > localhost: ICMP echo reply, id 5064, seq 1, length 64

11:15:41.807252 IP localhost > localhost: ICMP echo request, id 5064, seq 4, length 64

11:15:43.855203 IP localhost > localhost: ICMP echo request, id 5064, seq 6, length 64

11:15:43.855264 IP localhost > localhost: ICMP echo reply, id 5064, seq 6, length 64

11:15:45.903180 IP localhost > localhost: ICMP echo request, id 5064, seq 8, length 64

11:15:46.927181 IP localhost > localhost: ICMP echo request, id 5064, seq 9, length 64

11:15:47.951122 IP localhost > localhost: ICMP echo request, id 5064, seq 10, length 64

11:15:47.951166 IP localhost > localhost: ICMP echo reply, id 5064, seq 10, length 64

11:15:48.978638 IP localhost > localhost: ICMP echo request, id 5064, seq 11, length 64

11:15:48.978658 IP localhost > localhost: ICMP echo reply, id 5064, seq 11, length 64

11:15:49.999221 IP localhost > localhost: ICMP echo request, id 5064, seq 12, length 64

11:15:49.999283 IP localhost > localhost: ICMP echo reply, id 5064, seq 12, length 64

11:15:51.023158 IP localhost > localhost: ICMP echo request, id 5064, seq 13, length 64

11:15:51.023220 IP localhost > localhost: ICMP echo reply, id 5064, seq 13, length 64

11:15:56.143139 IP localhost > localhost: ICMP echo request, id 5064, seq 18, length 64

11:15:58.191097 IP localhost > localhost: ICMP echo request, id 5064, seq 20, length 64

11:15:58.191161 IP localhost > localhost: ICMP echo reply, id 5064, seq 20, length 64

11:16:00.239144 IP localhost > localhost: ICMP echo request, id 5064, seq 22, length 64

11:16:00.239206 IP localhost > localhost: ICMP echo reply, id 5064, seq 22, length 64

11:16:02.287209 IP localhost > localhost: ICMP echo request, id 5064, seq 24, length 64

11:16:02.287274 IP localhost > localhost: ICMP echo reply, id 5064, seq 24, length 64

11:16:03.311171 IP localhost > localhost: ICMP echo request, id 5064, seq 25, length 64

11:16:03.311235 IP localhost > localhost: ICMP echo reply, id 5064, seq 25, length 64

11:16:04.335163 IP localhost > localhost: ICMP echo request, id 5064, seq 26, length 64

11:16:04.335226 IP localhost > localhost: ICMP echo reply, id 5064, seq 26, length 64

11:16:05.359164 IP localhost > localhost: ICMP echo request, id 5064, seq 27, length 64

11:16:05.359226 IP localhost > localhost: ICMP echo reply, id 5064, seq 27, length 64

11:16:07.407226 IP localhost > localhost: ICMP echo request, id 5064, seq 29, length 64

11:16:07.407292 IP localhost > localhost: ICMP echo reply, id 5064, seq 29, length 64

11:16:11.503163 IP localhost > localhost: ICMP echo request, id 5064, seq 33, length 64

11:16:11.503228 IP localhost > localhost: ICMP echo reply, id 5064, seq 33, length 64

 

Am I doing something wrong?

lee42x

Thank you for the input.  

Yes, netem is dropping output packets. We can see from your ping response that only some of the packes recieved successful replys. What we cannot see is the application "ping" sending the requests that are getting dropped by netem.

Perhaps a better method is to use: 

iptables -A INPUT -m statistic --mode random --probability .4 -i lo -j DROP 

However if you have existing iptables or firewalld rules set this could cause a problem. 

This will be corrected in the next version of the class, thank you for the input.