The journey of an internet packet: Exploring networks with traceroute

Post by rudasn » Wed, Aug 28, 2024, 8:25 PM UTC

wang_li wrote: post #36

nullindividual wrote: post #28

This is a significantly better technical presentation on how traceroute works[0]; for example, unlike the illustrations in the linked article, traceroute does not necessarily take a symmetrical return path; the return path is hidden from the client -- the client only sees the forward path. [0] https://archive.nanog.org/sites/default/files/traceroute-201...

Traceroute doesn't even show you a path. It shows you a bunch of devices that happened to have a packet when its TTL expired. Every item listed in traceroute's output is a different packet and can take a different path towards the destination. On a different subject, why are people writing blogs about topics that are in the "literature" already?

Post by dkga » Wed, Aug 28, 2024, 8:38 PM UTC

Post by codethief » Wed, Aug 28, 2024, 9:24 PM UTC

archgoon wrote: post #60

myself248 wrote: post #51

Earlier quoted context omitted.

When everything's happy and packets are flowing as they should, there's absolutely nothing wrong with living at whatever layer of abstraction you wish. But when something is broken, troubleshooting is a different animal. When people make assumptions based on their abstractions, they can waste a lot of time chasing a problem that can't exist, because the abstraction hides several more layers of complexity. Their menta…

Sounds like fun :) You should write up a blog post where you had to debug some weird gnarly issues. A lot of us higher up the tech stack are pretty far removed from the signals level issues you're talking about but would love to hear about a low level debug session!

Post by remram » Wed, Aug 28, 2024, 9:44 PM UTC

RandomThoughts3 wrote: post #34

myself248 wrote: post #23

Traceroute doesn't see 90% of the machines your packet passes through. When your packet leaves a router at some-pop-some-port-wherever, that fiber isn't usually the same piece of glass that plugs into the next hop. There's a whole chain of amplifiers and possibly multiplexers that handle it between here and there. Some of those provide reliable transport service, giving you the illusion of a fiber that never breaks,…

The OSI model exists for a reason. You don't think about the life of the electrons going through your processors when you code. Traceroute is a view at a certain level of abstraction. It also doesn't tell you if your packet was delivered using ethernet, wifi or a token ring. It just doesn't matter.

Post by myself248 » Wed, Aug 28, 2024, 11:13 PM UTC

icehawk wrote: post #85

myself248 wrote: post #23

Traceroute doesn't see 90% of the machines your packet passes through. When your packet leaves a router at some-pop-some-port-wherever, that fiber isn't usually the same piece of glass that plugs into the next hop. There's a whole chain of amplifiers and possibly multiplexers that handle it between here and there. Some of those provide reliable transport service, giving you the illusion of a fiber that never breaks,…

The smart man knows all of these things exist. The wise man understands when these things matter. DWDM protected waves, MPLS, etc, are all out of scope when someone does a traceroute, finds their traffic is going to Europe asks me about it, and then I see a local upstream has picked up Cogent as a transit provider, and Cogent is preferring their customer routes over routes from their Tier 1 settlement free peers. But…