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tolsadus/networking.md

Last active July 8, 2016 09:24
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networking.md
  1. if you’re on (most modern distributions of) linux, forget that route(1) even exists (and throw ifconfig out in the same go) because it’s just absolutely frustrating. for probably 98% of what you need, ip(1) is the cool you care about

generally speaking, these will cover you: ip route, ip address, ip link

  1. when dealing with routing problems (​even if just two hosts next to each other​), mtr > traceroute > ping is an order that’s useful for a lot of what you need

mtr is nice because you can just let it keep running. press d in its display to get a running history breakdown of packets. fantastic for intermittent issues!

traceroute is generally known already, but depending on the complexity of your networks in question you may want traceroute-nanog or similar other ones. some of these are ASN-aware, which is useful.

in the same breath as traceroute, something else that’s useful to know about is tracepath

it’s a little bit nicer on finding asymm paths

lastly, ping ​is​ still useful in this, but if you need to start forcing specific kind of pings (pinning a specific source address, forcing a specific source interface, etc), sometimes fping can be slightly easier, so do be aware of it as well

oh and re tcpdump, a small gotcha to also be aware of: if you do something like tcpdump -nvi any -s 0 ….[filters here]…, you can get weird MAC stuff because of it capturing in promiscuous mode.

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the wisdom of @froztbyte

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