[Bug 1825649] [NEW] ISC DHCP client/Ubuntu fails to connect to commercial routers and code fix suggestion

[Glen Wetzel]

Public bug reported:

Linux systems (Ubuntu 16.04) fail to connect to various hotels with wifi
as a result of the DHCPDiscover message being sent by dhclient.  The
same laptop using MSWindows connects with the hotels without a problem.
This has been observed at multiple locations.

The problem was isolated by making the DHCPDiscover packet sent by
dhclient match the DHCPDiscover packet sent by MSWindows. It was found
that affecting difference was that dhclient generated a non-zero value
for the TOS UDP field.  Commenting out the setting of ip.ip_tos in
packet.c so that the field remained zero fixed the problem:

dhcp-4.4.1/common:

$ diff packet.c packet.c.orig
150c150
< //    ip.ip_tos = IPTOS_LOWDELAY;
---
>       ip.ip_tos = IPTOS_LOWDELAY;

The hotel's router may have been misconfigured to interpret the TOS
field.  However, the hotel connects to MSWindows/Apple devices.  As a
result, open source systems such as Ubuntu (Linux) gain a reputation of
being unreliable.  (My wife wants/needs to use MS/Apple systems as
result)

I would like to suggest that if the default DHCP message content
generated by MSWindows/Apple adheres to standards, then the default DHCP
message content from open source systems (linux) match bit for bit.
Sniff packets and compare to verify.  Such practice would assure that
open source connectivity (linux) is no less reliable than commercial
device connectivity.

** Affects: isc-dhcp (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1825649

Title:
  ISC DHCP client/Ubuntu fails to connect to commercial routers and code
  fix suggestion

Status in isc-dhcp package in Ubuntu:
  New

Bug description:
  Linux systems (Ubuntu 16.04) fail to connect to various hotels with
  wifi as a result of the DHCPDiscover message being sent by dhclient.
  The same laptop using MSWindows connects with the hotels without a
  problem.  This has been observed at multiple locations.

  The problem was isolated by making the DHCPDiscover packet sent by
  dhclient match the DHCPDiscover packet sent by MSWindows. It was found
  that affecting difference was that dhclient generated a non-zero value
  for the TOS UDP field.  Commenting out the setting of ip.ip_tos in
  packet.c so that the field remained zero fixed the problem:

  dhcp-4.4.1/common:

  $ diff packet.c packet.c.orig
  150c150
  < //    ip.ip_tos = IPTOS_LOWDELAY;
  ---
  >       ip.ip_tos = IPTOS_LOWDELAY;

  The hotel's router may have been misconfigured to interpret the TOS
  field.  However, the hotel connects to MSWindows/Apple devices.  As a
  result, open source systems such as Ubuntu (Linux) gain a reputation
  of being unreliable.  (My wife wants/needs to use MS/Apple systems as
  result)

  I would like to suggest that if the default DHCP message content
  generated by MSWindows/Apple adheres to standards, then the default
  DHCP message content from open source systems (linux) match bit for
  bit.  Sniff packets and compare to verify.  Such practice would assure
  that open source connectivity (linux) is no less reliable than
  commercial device connectivity.

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