15 254 ms 266 ms 267 ms p14-0.core01.tpa01.atlas.cogentco.com [220.127.116.11
16 270 ms 229 ms 268 ms vl3509.na22.b001841-0.tpa01.atlas.cogentco.com [
17 270 ms 269 ms 264 ms ceridius.demarc.cogentco.com [18.104.22.168]
18 269 ms 264 ms 267 ms 22.214.171.124
19 * 269 ms * 66.232.100.XXX
20 263 ms 269 ms 281 ms 66.232.100.XXX
Traceroute works by sending out packets and step incrementing the Time To Live (TTL). This counter is decremented by each router that touches the packet, and the packet is discarded when the counter gets down to 0. This counter is used to prevent packets from being forwarded forever in the event of a routing loop. When the counter gets to 0, the router tosses the packet and sends an ICMP TTL Exceeded message back to the source IP so that the station knows packets are being discarded. Traceroute watches for those responses and uses it to build the list of hops it displays, with the 3 numbers you see being the return results from 3 test packets sent for each TTL interval.
So in your case, either some of your packets occasionally find a path with a shorter hop-count so that the destination is reached earlier than expected with the TTL discovery mechanism, or there is a firewall at that hop that is spoofing the TTL Exceeded returns.
Enterprise Network Engineer :: Hosting Hobbyist :: Master of Procrastination
"The really cool thing about facts is they remain true regardless of who states them."
MTR is a traceroute program that, once it determines the path via traceroute, starts to continuously ping each of the hops so you can find where your packet loss is starting. It's available in most of the distributions for linux ('apt-get install mtr' or 'yum install mtr'), but you can also get the Linux version here:
Most people make the mistake of blaming the hops 2 and 4, but that would just indicate those routers are throttling their ICMP responses. Since you have to route *through* hop 2 and hop 4 to get to hop 6, you can't be losing packets in the middle of the trace and have 0% packet loss at the end.