ICMP, Ping, and Traceroute – What I wish I was taught (2020)

Post by nickstinemates » Thu, Jul 28, 2022, 3:25 PM UTC

csydas wrote: post #30

Hikikomori wrote: post #18

Earlier quoted context omitted.

I wouldn't call the details he goes into with traceroute "just basics", its common even for network engineers to come to the wrong conclusion based on traceroute output, or not realising that they need more information to truly know what is going on (traceroute from both sides).

I would second this. I handle a lot of meetings and screenings for technical positions and quite a few Senior Network Administrators don't know or remember the basics for a lot of networking items and are completely lost when it comes to items like this. It is very much so a prevalent problem that many IT persons don't realize it's not only possible, but common to block ICMP entirely. For me, this has rendered ping u…

Post by neilv » Thu, Jul 28, 2022, 4:17 PM UTC

tedd4u wrote: post #8

Tip for tracerouters ... use mtr instead brew install mtr Try tapping 'd' twice to enable a stripchart ? for help My traceroute [v0.95] xxxxxxxx.local (172.16.0.2) -> news.ycombinator.com (50.1122022-07-27T23:37 Keys: Help Display mode Restart statistics Order of fields quit Packets Pings Host Loss% Snt Last Avg Best Wrst StDev 1. 172.16.0.1 0.0% 14 15.4 17.6 14.1 20.5 2.2 2. (waiting for reply) 3. 162.158.164.5 14.3…

    sudo apt install mtr-tiny

Post by Bluecobra » Thu, Jul 28, 2022, 5:17 PM UTC

  >ping 0x08080808
  
  Pinging 8.8.8.8 with 32 bytes of data:
  Reply from 8.8.8.8: bytes=32 time=4ms TTL=58
  Reply from 8.8.8.8: bytes=32 time=4ms TTL=58
  Reply from 8.8.8.8: bytes=32 time=4ms TTL=58
  Reply from 8.8.8.8: bytes=32 time=4ms TTL=58

Post by JackGreyhat » Thu, Jul 28, 2022, 8:53 PM UTC

psim1 wrote: post #32

ping and traceroute used to be very useful tools. Then for a period of time -- maybe still ongoing -- sysadmins and some network security folks decided that by blocking ALL ICMP at their network edge, they were increasing security. (Wrong!) As a result, you get hanging traceroutes with one or two hops left and you can't use ping to verify a host is online. Worse, blocking all ICMP breaks things like MTU discovery alo…

Post by tedd4u » Sat, Jul 30, 2022, 2:47 AM UTC

sim7c00 wrote: post #34

tedd4u wrote: post #8

Tip for tracerouters ... use mtr instead brew install mtr Try tapping 'd' twice to enable a stripchart ? for help My traceroute [v0.95] xxxxxxxx.local (172.16.0.2) -> news.ycombinator.com (50.1122022-07-27T23:37 Keys: Help Display mode Restart statistics Order of fields quit Packets Pings Host Loss% Snt Last Avg Best Wrst StDev 1. 172.16.0.1 0.0% 14 15.4 17.6 14.1 20.5 2.2 2. (waiting for reply) 3. 162.158.164.5 14.3…

why?

  • See the whole path fast - don't wait on one unresponsive hop to see "deeper" hosts
  • Run ongoing traces to get path quality (per-hop packet drop & latency min/max/avg)
  • Optional jitter statistics
  • Color "strip chart" view (press 'd' twice)
  • Drawback: need sudo, unlike trace route