Why does traceroute -T add hops and intermediary asterisks?

Question

Behold, traceroute without any options:

$ traceroute google.com
traceroute to google.com (172.217.4.142), 30 hops max, 60 byte packets
 1  10.14.62.1 (10.14.62.1)  0.619 ms  0.685 ms  0.806 ms
 2  10.14.255.29 (10.14.255.29)  0.492 ms  0.508 ms  0.508 ms
 3  c2-dc-cs02_po81.microchip.com (10.10.255.54)  1.199 ms  1.210 ms  1.507 ms
 4  c2-dc-wr02_pc20.microchip.com (10.10.255.155)  0.489 ms  0.565 ms  0.565 ms
 5  c2-dc-cp02_int.microchip.com (10.10.202.62)  3.040 ms  3.394 ms  3.403 ms
 6  c2-dc-er01.microchip.com (198.175.253.66)  4.525 ms  4.141 ms  3.994 ms
 7  ge-10-2-9.mpr3.phx2.us.above.net (64.124.198.17)  5.893 ms  5.893 ms  5.089 ms
 8  ae28.cs1.lax112.us.eth.zayo.com (64.125.31.252)  12.306 ms  12.547 ms  12.220 ms
 9  * * *
10  64.125.13.109 (64.125.13.109)  12.742 ms  12.433 ms  12.782 ms
11  108.170.247.225 (108.170.247.225)  13.210 ms  12.447 ms  12.799 ms
12  72.14.239.121 (72.14.239.121)  13.587 ms 72.14.238.213 (72.14.238.213)  12.143 ms  12.546 ms
13  lax17s14-in-f14.1e100.net (172.217.4.142)  12.556 ms  10.660 ms  10.771 ms

But, if I add -T:

$ sudo traceroute -T google.com
traceroute to google.com (172.217.4.142), 30 hops max, 60 byte packets
 1  10.14.62.1 (10.14.62.1)  0.513 ms  0.660 ms  0.661 ms
 2  10.14.255.29 (10.14.255.29)  0.450 ms  0.449 ms  0.484 ms
 3  c2-dc-cs02_po81.microchip.com (10.10.255.54)  1.247 ms  1.246 ms  1.574 ms
 4  10.10.255.166 (10.10.255.166)  0.388 ms  0.424 ms  0.423 ms
 5  * * *
 6  * * *
 7  * * *
 8  * * *
 9  * * *
10  * * *
11  * * *
12  * * *
13  * * *
14  * * *
15  lax17s14-in-f142.1e100.net (172.217.4.142)  99.545 ms  99.616 ms  11.428 ms

score 1 · Answer 1 · answered Dec 06 '17 at 01:53

By default traceroute uses UDP packets. With the -T option it uses TCP packets. Active elements on the network between your computer and the server you try to reach may behave differently between UDP and TCP. In most cases UDP packets are more heavily filtered, and the TCP version of traceroute gives better information. You seem to be in an opposite case, but then your destination is kind of special as it is heavily anycasted with many other tricks.

Why does traceroute -T add hops and intermediary asterisks?

1 Answers1