44076fbd42
Proof-reading much easier when Markdown is rendered in the browser. Change-Id: Ia173dea817866d214547546bc3428ac6fe6782bf Reviewed-on: https://cl.tvl.fyi/c/depot/+/7305 Tested-by: BuildkiteCI Reviewed-by: wpcarro <wpcarro@gmail.com> Autosubmit: wpcarro <wpcarro@gmail.com>
63 lines
1.6 KiB
Markdown
63 lines
1.6 KiB
Markdown
## Background
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Let's say we'd like to debug a remote machine but use some of the debugging
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tools we have on our local machine like wireshark.
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You *can* run `tcpdump` on the remote and then `scp` the file to your local
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machine to analyze the traffic, but after doing that a few times you may want a
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workflow with a tighter feedback loop. For this we'll forward traffic from a
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remote machine to our local machine.
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**Note:** There's also `termshark`, which is a `wireshark` TUI that you can run
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on the remote. It's quite cool!
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## Local
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Run the following on your local machine to forward your remote's traffic:
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```shell
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λ ssh -R 4317:127.0.0.1:4317 -N -f user@remote
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```
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Here is an abridged explanation of the flags we're passing from `man ssh`:
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```
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-N Do not execute a remote command. This is useful for just forwarding ports.
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-f Requests ssh to go to background just before command execution.
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```
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**Note:** I couldn't find a good explanation for the `-R` option, so I tried
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removing it and re-running the command, but that results in a resolution error:
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```
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ssh: Could not resolve hostname 4317:127.0.0.1:4317: Name or service not known
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```
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The remote should now be forwarding traffic from port `4317` to our
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machine.
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## Testing
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Let's generate some traffic on the remote:
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```shell
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λ telnet localhost 4317
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Trying ::1...
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Connected to localhost.
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Escape character is '^]'.
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hello
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world
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```
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Locally you should see:
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```shell
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λ nc -l 4317 -k # run this *before* running the above command
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hello
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world
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```
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You should now be able to `tcpdump -i lo port 4317` or just use `wireshark`
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locally.
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Happy debugging!
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