tree 3b5d45127c17948735d5877ec0071ff1d74b6527
parent 37b237bfbed17a0d1026defd1d15150fcd92095d
author Denton Gentry <dgentry@google.com> 1449337149 -0800
committer Denton Gentry <dgentry@google.com> 1457359716 -0800

dhcp-rogue: use raw socket and output on one line.

1. Socket usage
  Using a UDP socket sends the packet with a source IP address
  of our own IP, like 192.168.1.1. Other GFiber Network Boxes
  on the LAN will respond because we set the "dhcp-authoritative"
  config option in dnsmasq, but many DHCP servers will ignore
  these DHCP Discover frames. Therefore we are not reliably
  detecting other nearby DHCP servers.

  Fix this by using a PF_PACKET socket, and filling out the
  IP and UDP headers ourself. We set the source IP to 0.0.0.0.

  PF_PACKET goes straight out on the wire, so the local dnsmasq
  (if any) does not see it. So additionally send a DHCP Discover
  on a PF_INET socket, to be able to monitor the local dnsmasq.

2. Print on one line
  Printing each response as it arrives is really only useful
  for humans looking at the result. Gather all responses and
  print them on one line, so monitoring can look for cases where
  >1 server responded.

3. Increase timeout to 15 seconds
  Noticed that Comcast's DHCP servers routinely take about 5
  seconds to respond, so a 5 second timeout isn't reliable.
  Make the timeout longer.

b/27441248

Change-Id: Iaa690ec21ce6069b3b5d37e6b455845e9b00e37b