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265 points night-rider | 2 comments | | HN request time: 0.411s | source
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commandersaki ◴[] No.38590611[source]
Copying the per-hop loss indicator from mtr is a bad decision in my opinion. It's always been a source of incorrect diagnosis of network issues. The only loss that matters is end to end.
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lathiat ◴[] No.38591120[source]
That is not entirely true. Sure it’s not a 100% reliable signal as routing is asymmetric but it also often isn’t and also gives you an idea of which point to ask first at least.

If the packet loss starts at your wifi router, or your ISPs router. Or the next hop after you ISP. That all gives you a bit of an idea where the problem likely is. I solve problems like that all the time.

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commandersaki ◴[] No.38591827[source]
I was a network engineer for over a decade in hosting datacenter environments and would get false reports of packet loss to various destinations because people would use MTR and say they see loss on the path. If a packet takes the path A -> B -> C and pings to B have 50% loss but pings to C have 0% loss, then the path is perfectly fine.

The only way to reliably isolate packet loss to a hop on the path is to have a destination for testing where packets pass through that hop and is in its bailiwick which doesn't perform rate limiting or policing of ICMP traffic.

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FujiApple ◴[] No.38591945[source]
Something I intend to add to Trippy, but have not got around to it yet; is to codify the "If a packet takes the path A -> B -> C and pings to B have 50% loss but pings to C have 0% loss, then the path is perfectly fine" idea and use that to produce more meaningful headline status information to the user. How would you codify this?
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1. linsomniac ◴[] No.38592597[source]
It's probably tricky but if there's loss at D, maybe only then materialize the display of the loss backwards until there is no loss: C? B? A? It gets tricky though where maybe there is a small loss at D, but say that C and B have chronic loss because of throttling in the slow path responses.

If D has 1% loss and B and C have 50%, is it fair to say A=0, B=1%, C=1%, D=1%?

MTR display of loss is indeed confusing, but when weird things are going on it can be helpful just stare at it a while to see what's going on. Trippy looks fantastic, and I need to play with it, but there are cases where I just want to stare at the path loss for a while.

There's no way to influence the TTL on TTL timed-out responses, is there? That'd be pretty cool if there were some way to get the return path of the intermediaries to reply.

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2. FujiApple ◴[] No.38596571[source]
Thanks for that, I'll give this some thought and write a proposal in this [0] placeholder issue.

[0] https://github.com/fujiapple852/trippy/issues/860