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How to track down external network issue? (lemmy.world)

submitted 4 months ago by atfergs@lemmy.world to c/homelab@lemmy.ml

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I've got a homelab running a number of services in Docker. Everything works beautifully internally, but access from outside the network is very slow. I'm using nginx proxy manager and cloudflare ddns for the external access. It's not a speed issue. I'm on fiber with a very solid upload.

Jellyfin and Overseerr are the main services that I'm having trouble with. Oddly, once you manage to get a video going in Jellyfin, it works fine.

I could use some guidance in what to look for, what tools I can use, or any other advice on how to track down the issue. Thanks!

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[–] hatedbad@lemmy.sdf.org 2 points 4 months ago (2 children)

start with basics:

install iperf on every device you can between an external device and your internal host(s) and use it to find any bottlenecks
use tools like tcpdump to analyze packets flowing over the network. you can often find surprising results this way
start with a simple test best (again, iperf) with the most simple config (no nginx etc) and add the complexity of your config bit by bit until the issue returns

[–] litchralee@sh.itjust.works 3 points 4 months ago* (last edited 4 months ago)

Regarding tcpdump, you can use it directly from the command line to print out packets, or you can have it record traffic to a file. That file can later be opened in Wireshark for analysis, with filters, color, ~~blackjack and hookers~~, and protocol decoding.

Things like TCP retries or MTU issues/fragmentation will be very apparent when presented in Wireshark.

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