tree 003afaa7512c8686e3e2e155a120f7ef160765a7
parent b0f2f25fec90bf0a22fc54b88d20bddfa08fd85e
author David Crawshaw <crawshaw@google.com> 1491498796 -0400
committer David Crawshaw <crawshaw@golang.org> 1491512517 -0400

dhcp: handle multiple DHCP servers

The client was not being careful enough and could be confused by
multiple DHCP servers on a network.

After sending a DISCOVER, the client would recieve two OFFERs.
It would Read() the first, send a REQUEST, and then Read() again
waiting for an ACK. The first thing the second Read() got was a
second OFFER. This was being mis-interpreted as a bad ACK, and
the process started over. A successful DHCP connection required
everything to be negotiated with one server before the other
responded, which could take minutes.

This CL explicitly checks the incoming message types, so
subsequent OFFER messages can be ignored.

It also fixes a small server bug: an incoming REQUEST for a
different server should be ignored, not NAKed.

This deals with the first problem in NET-43.

Change-Id: I133b1183c2a019041cd47d9bfaf4e09eb97cfcd3