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network reference v2: questions about allow-hotplug


I have been looking at the wiki version of the network reference
[ http://wiki.debian.org/DebianReference/Network ]

I have a few questions about the description of "allow-hotplug", which
I think could be improved further. I have always found the documentation
for this stanza difficult to understand, both in the Reference and in

Question 1.
In the table of stanzas, you have this line
| "allow-hotplug <interface_name>" |
  To start interface <interface_name> upon hotplug event of the system. |

I take this to mean that there is hotplug support in the ifupdown
programs, so that they can respond to hotplug events from the kernel.
Is that correct?
Would it be better to say it this way?
| "allow-hotplug <interface_name>" |
  Start interface <interface_name> when the kernel detects a hotplug event
   from the interface. |

Question 2.
Under "The network interface served by the DHCP" is the sentence:
   The following configuration entry in the /e/n/i file brings up the
   primary network interface eth0 upon the Linux kernel finding up the
   physical interface eth0 (via allow-hotplug stanza) while configuring
   it with DHCP.

Would it be better to say this?
   The following configuration entry in the /e/n/i file is the typical
   way to set up a network interface in such an environment. When the
   Linux kernel detects the physical interface eth0, the allow-hotplug
   stanza will cause ifup to bring up the interface and the iface stanza
   will cause ifup to use DHCP to configure the interface.

Question 3.

If I understand correctly the "hotplug events" referred to here are
relating to the network hardware being hotplugged into a running system,
eg a PCMCIA card being inserted or a USB ethernet device being plugged in.

When a system with a built-in ethernet card is powered up, is a hotplug
event generated when the kernel detects it, during the boot sequence?

Question 4.
If I power up a system with a built-in ethernet interface, but with
no ethernet cable plugged into it, does plugging in an ethernet cable
also generate a hotplug event that is noticed by allow-hotplug?

This last part is the piece I find most confusing. The section on the
wiki page about "The caution for operations" helped quite a bit,
explaining that if one is using ifplugd then "auto" and "allow-hotplug"
should not be used. I think that is the first time I have seen that
written down clearly.

The section "auto-switchable network configuration" hints that the
answer here is yes, plugging in an ethernet cable generates a hotplug
event that allow-hotplug will act upon.
If so, does that mean ifplugd is no longer needed?

Question 5.
At the top of the page it explains:
  This section will address network setup for the mobile PC which moves
  around different networks. (For the non-mobile PC, the debian-installer
  should have taken care your network setup and there are almost nothing
  for us to play with.)
I think that it would be worth including a short subsection describing
how a non-mobile PC is normally set up. What do others think?
For example:

  == Non-mobile PCs ==
  Systems that are normally permanently attached to a single network
  should have been correctly configured by the debian-installer.
  Typically the /e/n/i file looks like this:
  auto lo
  iface lo inet loopback
  auto eth0
  iface etho inet dhcp
  In some cases the host may have a static IP configuration for eth0,
  like that shown in "The network interface with static IP".

  Non-mobile systems typically do not need the {{{resolvconf}}} package;
  their name resolution can be set up via DHCP or by manual editing of

Yes, this is a bit redundant but I think it might help readers looking
for authoritative information on setting up their LAN machines.

Kind regards
Vincent McIntyre                                vmcintyr@atnf.csiro.au
Australia Telescope National Facility, CSIRO     voice:+61-2-9372-4643
PO Box 76, Epping, NSW 1710, AUSTRALIA             fax:+61-2-9372-4442

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