mtr misses last packet in report mode for high latency hops

[Ted]

mtr always misses the last packet in report mode for high latency last hops and reports that as packet loss.

For example if you are in Europe or USA this can be always reproduced running mtr to host "auspost.com.au" in report mode. If running in non report mode there would be no packet loss reported.

Please see examples below. Note that loss of 50% for the last few hops if the cycle count for mtr is set to 2. If set to 3, the packet loss would always be 33% for those hops, if count is set to 10 - 10% loss and so on.

user@myhostname:~$ mtr --report -n -c 2 auspost.com.au
HOST: myhostname Loss% Snt Last Avg Best Wrst StDev
  1.|-- 192.168.0.1 0.0% 2 0.3 0.3 0.3 0.4 0.1
  2.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
  3.|-- 213.190.41.21 0.0% 2 0.6 0.7 0.6 0.7 0.1
  4.|-- 82.135.182.1 0.0% 2 0.7 0.7 0.7 0.7 0.0
  5.|-- 213.248.85.89 0.0% 2 11.5 11.5 11.5 11.5 0.0
  6.|-- 80.91.251.35 0.0% 2 26.2 25.8 25.5 26.2 0.5
  7.|-- 213.155.131.247 0.0% 2 120.1 120.1 120.1 120.1 0.0
    | `|-- 213.155.131.245
  8.|-- 213.155.135.157 0.0% 2 197.6 196.0 194.5 197.6 2.2
  9.|-- 80.239.167.182 0.0% 2 201.4 200.2 198.9 201.4 1.8
 10.|-- 203.208.148.90 50.0% 2 357.5 357.5 357.5 357.5 0.0
 11.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
 12.|-- 119.225.138.30 50.0% 2 376.0 376.0 376.0 376.0 0.0
 13.|-- 172.16.16.186 50.0% 2 378.9 378.9 378.9 378.9 0.0
 14.|-- 172.16.16.92 50.0% 2 384.5 384.5 384.5 384.5 0.0
 15.|-- 202.58.62.160 50.0% 2 383.7 383.7 383.7 383.7 0.0

user@myhostname:~$ mtr --report -n -c 3 auspost.com.au
HOST: myhostname Loss% Snt Last Avg Best Wrst StDev
  1.|-- 192.168.0.1 0.0% 3 0.3 0.3 0.2 0.5 0.1
  2.|-- ??? 100.0 3 0.0 0.0 0.0 0.0 0.0
  3.|-- 213.190.41.21 66.7% 3 20.8 20.8 20.8 20.8 0.0
  4.|-- 82.135.182.1 0.0% 3 0.6 0.7 0.6 0.8 0.1
  5.|-- 213.248.85.89 0.0% 3 11.5 11.5 11.5 11.5 0.0
  6.|-- 80.91.251.35 0.0% 3 25.4 39.7 25.4 68.2 24.7
  7.|-- 213.155.131.247 0.0% 3 199.6 181.0 120.1 223.3 54.1
  8.|-- 80.91.248.188 0.0% 3 194.4 194.0 193.0 194.5 0.9
    | `|-- 213.155.135.157
  9.|-- 195.12.255.234 0.0% 3 198.9 197.2 193.9 198.9 2.9
    | `|-- 80.239.167.182
 10.|-- 203.208.148.90 0.0% 3 358.2 358.0 357.6 358.3 0.4
 11.|-- ??? 100.0 3 0.0 0.0 0.0 0.0 0.0
 12.|-- 119.225.138.30 33.3% 3 377.2 376.6 376.0 377.2 0.9
 13.|-- 172.16.16.186 33.3% 3 378.2 380.1 378.2 382.0 2.7
 14.|-- 172.16.16.92 33.3% 3 384.2 384.2 384.2 384.3 0.0
 15.|-- 202.58.62.160 33.3% 3 384.5 383.1 381.7 384.5 2.0

user@myhostname:~$ mtr --report -n -c 10 auspost.com.au
HOST: myhostname Loss% Snt Last Avg Best Wrst StDev
  1.|-- 192.168.0.1 0.0% 10 0.3 0.3 0.2 0.4 0.0
  2.|-- ??? 100.0 10 0.0 0.0 0.0 0.0 0.0
  3.|-- 213.190.41.21 20.0% 10 0.6 4.6 0.6 29.2 10.0
  4.|-- 82.135.182.1 0.0% 10 0.7 1.8 0.6 11.8 3.5
  5.|-- 213.248.85.89 0.0% 10 11.4 15.5 11.4 48.0 11.5
  6.|-- 80.91.251.35 0.0% 10 25.4 37.4 25.3 111.9 27.7
  7.|-- 213.155.131.245 0.0% 10 165.0 131.9 120.0 165.0 19.2
    | `|-- 213.155.131.247
  8.|-- 213.155.135.157 0.0% 10 194.4 197.0 192.9 223.7 9.4
    | `|-- 80.91.248.188
  9.|-- 80.239.167.182 0.0% 10 193.9 206.1 193.9 278.6 25.7
    | `|-- 195.12.255.234
 10.|-- 203.208.148.90 0.0% 10 358.0 357.7 357.5 358.1 0.2
 11.|-- ??? 100.0 10 0.0 0.0 0.0 0.0 0.0
 12.|-- 119.225.138.30 10.0% 10 375.9 376.5 375.9 379.1 1.0
 13.|-- 172.16.16.186 10.0% 10 378.8 378.6 378.2 379.1 0.4
 14.|-- 172.16.16.92 10.0% 10 384.3 384.6 384.2 385.2 0.4
 15.|-- 202.58.62.160 10.0% 10 383.5 381.4 378.4 383.5 2.1

[Ted (ainisb)]

It seems that this bug was already fixed in version 0.81 of mtr (see link below), but the fix was not integrated into ubuntu package. I tested mtr on 3 different machines running Ubuntu Oneiric and Natty and in all cases this problem was present. Also it seems this will be affecting Ubuntu 12.04 Precise Pangolin

https://bugs.launchpad.net/mtr/+bug/776211

[Sven Schmidt (svenne-svenne)]

I can see the same issue on 12.04-1. It seems mtr 0.80(included in precise 12.04) and also 0.82(included in 12.10) are having this bug. Running the mtr without report switch won't show lost packets. So it seems some bug in the reporting code.

sven@Ubuntu1204-1:~$ mtr -nrc 2 webmail.optuszoo.com.au
HOST: Ubuntu1204-1 Loss% Snt Last Avg Best Wrst StDev
  1.|-- 192.168.178.1 0.0% 2 0.7 0.9 0.7 1.1 0.2
  2.|-- 62.214.64.79 0.0% 2 39.5 39.6 39.5 39.7 0.2
  3.|-- 62.214.109.13 0.0% 2 41.3 41.1 40.8 41.3 0.4
  4.|-- 62.214.110.245 0.0% 2 39.6 39.9 39.6 40.2 0.4
  5.|-- 62.214.110.241 0.0% 2 41.0 40.9 40.8 41.0 0.1
  6.|-- 62.214.111.29 0.0% 2 39.8 40.4 39.8 41.1 0.9
  7.|-- 62.214.110.237 0.0% 2 113.4 77.1 40.7 113.4 51.4
  8.|-- 149.6.138.205 0.0% 2 45.7 43.0 40.3 45.7 3.9
  9.|-- 130.117.0.121 0.0% 2 43.0 43.9 43.0 44.8 1.3
 10.|-- 154.54.37.114 0.0% 2 54.2 54.6 54.2 55.1 0.6
 11.|-- 154.54.44.209 0.0% 2 124.6 124.9 124.6 125.3 0.5
 12.|-- 154.54.44.102 0.0% 2 132.4 131.5 130.6 132.4 1.3
 13.|-- 154.54.6.154 0.0% 2 146.9 146.0 145.1 146.9 1.3
 14.|-- 154.54.84.73 0.0% 2 158.7 158.4 158.1 158.7 0.4
 15.|-- 154.54.45.66 0.0% 2 196.4 196.2 196.1 196.4 0.2
 16.|-- 154.54.7.174 0.0% 2 195.3 195.4 195.3 195.5 0.2
 17.|-- 154.54.10.170 0.0% 2 195.6 195.3 194.9 195.6 0.6
 18.|-- 203.208.148.82 50.0% 2 345.0 345.0 345.0 345.0 0.0
 19.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
 20.|-- 210.49.105.6 50.0% 2 343.7 343.7 343.7 343.7 0.0
 21.|-- 211.29.129.38 50.0% 2 348.0 348.0 348.0 348.0 0.0
 22.|-- 211.29.129.213 50.0% 2 344.6 344.6 344.6 344.6 0.0
 23.|-- 211.29.129.202 50.0% 2 397.5 397.5 397.5 397.5 0.0
 24.|-- 211.29.132.83 50.0% 2 345.5 345.5 345.5 345.5 0.0

                            My traceroute [v0.82]
Ubuntu1204-1 (0.0.0.0) Fri Dec 14 11:54:42 2012
Keys: Help Display mode Restart statistics Order of fields quit
                                      Packets Pings
 Host Loss% Snt Last Avg Best Wrst StDev
 1. 192.168.178.1 0.0% 3 0.9 0.9 0.9 0.9 0.0
 2. 62.214.64.79 0.0% 3 38.1 51.0 38.1 72.7 18.9
 3. 62.214.109.13 0.0% 3 39.4 40.0 39.0 41.6 1.4
 4. 62.214.110.245 0.0% 2 195.7 117.2 38.6 195.7 111.1
 5. 62.214.110.241 0.0% 2 40.0 39.3 38.6 40.0 1.0
 6. 62.214.111.29 0.0% 2 39.9 54.2 39.9 68.6 20.3
 7. 62.214.110.237 0.0% 2 39.8 54.6 39.8 69.4 20.9
 8. 149.6.138.205 0.0% 2 41.5 53.8 41.5 66....

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Matt Nordhoff (mnordhoff)]

This has been fixed upstream -- again -- and ought to be in 0.86 when that gets released.

https://github.com/traviscross/mtr/commit/6ce1601b27fdd95b44ed65d7fd83604860276d63