Fun with IP address parsing

Post by j1elo » Sun, Dec 27, 2020, 1:28 AM UTC

  # Get main local IP address from the default external route (Internet gateway)
  iplan() {
      # Note: "1" is shorthand for "1.0.0.0"
      case "$OSTYPE" in
          linux*) ip -4 -oneline route get 1 | grep -Po 'src \K([\d.]+)' ;;
          darwin*) ipconfig getifaddr "$(route -n get 1 | sed -n 's/.*interface: //p')" ;;
      esac
  }

Post by Dylan16807 » Sun, Dec 27, 2020, 1:39 AM UTC

proactivesvcs wrote: post #24

I'm not convinced these are "cursed". They may be the result of bygone networking conventions, implementation ideas that never came to mainstream fruition, flexibility for use-cases etc. Just because we don't understand something that looks strange, doesn't mean it's cursed, nor that one can simply turn one's nose up and say "I don't understand why these exist so I'll just ignore them when I implement x".

Post by anderskaseorg » Sun, Dec 27, 2020, 2:37 AM UTC

j1elo wrote: post #81

> It does not process Class A/B notation, or hex or octal notation. I got to find that notation useful once , to make a shorter one-liner... without even knowing that there were different classes of IPv4 address, and that I was looking at one of them. It's a tiny function that gives me the IP address of my machine in the LAN, for either Linux and Mac: # Get main local IP address from the default external route (Inter…

Post by icedchai » Sun, Dec 27, 2020, 3:10 AM UTC

the_mitsuhiko wrote: post #52

arkadiyt wrote: post #45

Earlier quoted context omitted.

IPv6 has internal ranges defined just like IPv4 does - anything in an internal range should be blocked, and anything in an external range is safe to pass through.

Since there is no NAT in an IPv6 deployment unsafe services you typically want to prevent access to look like non internal ranges. Whereas in your normal IPv4 deployment you might have your protected service on 192.168.4.111 with IPv6 it will just share the same prefix (potentially) as your host.

Post by cle » Sun, Dec 27, 2020, 4:18 AM UTC

icedchai wrote: post #87

the_mitsuhiko wrote: post #52

Earlier quoted context omitted.

Since there is no NAT in an IPv6 deployment unsafe services you typically want to prevent access to look like non internal ranges. Whereas in your normal IPv4 deployment you might have your protected service on 192.168.4.111 with IPv6 it will just share the same prefix (potentially) as your host.

NAT was meant to work around IP exhaustion issues, not act as a security layer. By accident, it often happens to provide some additional security. By keep in mind those "internal" IP addresses may be routable in some cases, due to either accidental or deliberate mis-configuration. IPv6, with end-to-end connectivity, is how the Internet is supposed to work. It's how it did work in the early 90's, even with IPv4. If yo…