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Old 07-29-2011, 04:10 PM
Itamar Reis Peixoto
 
Default Fwd: Rapid DHCP

Interesting message in another list.

for me fedora is very slow to get dhcp address.


---------- Forwarded message ----------
From: Sridhar Dhanapalan <sridhar@laptop.org.au>
Date: Fri, Jul 29, 2011 at 12:51 PM
Subject: Rapid DHCP
To: OLPC Devel <devel@lists.laptop.org>, OLPC Australia list
<olpc-au@lists.laptop.org>


Here's an article that tries to explain why Mac OS is so much faster
at connecting to networks than Linux and Windows:

http://cafbit.com/entry/rapid_dhcp_or_how_do

Could such an implementation be considered for the OLPC OS? XOs go on
and off the network all the time, as power management kicks in and the
machines move in and out of AP range (or switch to a different AP).
This is a disruptive process, and speeding it up would be welcome.

Sridhar



Sridhar Dhanapalan
Engineering Manager
One Laptop per Child Australia
M: +61 425 239 701
E: sridhar@laptop.org.au
A: G.P.O. Box 731
** * Sydney, NSW 2001
W: www.laptop.org.au
_______________________________________________
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Old 07-30-2011, 08:48 AM
Ryan Rix
 
Default Fwd: Rapid DHCP

On Fri 29 July 2011 13:10:34 Itamar Reis Peixoto wrote:
> Interesting message in another list.
>
> for me fedora is very slow to get dhcp address.

Reading the hackernews comments on it makes me wonder if this is a very good
idea. It may work for people in certain usecases, but in the case of Fedora
probably not so much

http://news.ycombinator.com/item?id=2756952
http://news.ycombinator.com/item?id=2757785

for examples

r

>
> ---------- Forwarded message ----------
> From: Sridhar Dhanapalan <sridhar@laptop.org.au>
> Date: Fri, Jul 29, 2011 at 12:51 PM
> Subject: Rapid DHCP
> To: OLPC Devel <devel@lists.laptop.org>, OLPC Australia list
> <olpc-au@lists.laptop.org>
>
>
> Here's an article that tries to explain why Mac OS is so much faster
> at connecting to networks than Linux and Windows:
>
> http://cafbit.com/entry/rapid_dhcp_or_how_do
>
> Could such an implementation be considered for the OLPC OS? XOs go on
> and off the network all the time, as power management kicks in and the
> machines move in and out of AP range (or switch to a different AP).
> This is a disruptive process, and speeding it up would be welcome.
>
> Sridhar
>
>
>
> Sridhar Dhanapalan
> Engineering Manager
> One Laptop per Child Australia
> M: +61 425 239 701
> E: sridhar@laptop.org.au
> A: G.P.O. Box 731
> Sydney, NSW 2001
> W: www.laptop.org.au
> _______________________________________________
> Devel mailing list
> Devel@lists.laptop.org
> http://lists.laptop.org/listinfo/devel
--
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_
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/_/

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Old 07-30-2011, 02:31 PM
Genes MailLists
 
Default Fwd: Rapid DHCP

On 07/30/2011 04:48 AM, Ryan Rix wrote:

...

> Reading the hackernews comments on it makes me wonder if this is a very good
> idea. It may work for people in certain usecases, but in the case of Fedora
> probably not so much
>
> http://news.ycombinator.com/item?id=2756952
> http://news.ycombinator.com/item?id=2757785

>> ---------- Forwarded message ----------

...

>>
>> http://cafbit.com/entry/rapid_dhcp_or_how_do
>

Hmm ... the complaint of changing IP does not seem to make sense - as I
read the article - the MAC simply remembers server info and instead of a
blind dhcp (which causes delays if you are now on a new network as the
dhcp server will not NAK a network for which is not authoritative), it
ARP's the remembered server first which is very fast - hard to see how
this would cause problems (shy of bugs of course)...

gene/
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Sat Jul 30 17:30:01 2011
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Subject: Re: [gentoo-dev] Warn users not to do separate /usr partition without
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References: <4E33B25F.3050606@gentoo.org> <20110730114600.0f787296@googlemail.com> <4E340D4B.8040403@gentoo.org>
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Samuli Suominen schrieb:
>=20
> Someone mentioned NFS mount on /usr. Do we have other reasons? How
> many users that might be?

If you have / encrypted, then you can leave /usr unencrypted as it
contains no secrets. Also /usr can remain mounted read-only most of the
time, so there is a reduced chance of accidental corruption.
I don't know the number of users who might want this, and I imagine it
is difficult to count them.

> I dislike the idea of moving libglib-2.0, libdbus-1, libdbus-glib-1, an=
d
> couple of dozen more libs to /

If you say that /usr must be on the same filesystem as /, then there is
no real reason to not just make a symlink /usr -> .


Best regards,
Ch=C3=AD-Thanh Christopher Nguy=E1=BB=85n
 
Old 07-30-2011, 02:37 PM
Lennart Poettering
 
Default Fwd: Rapid DHCP

On Sat, 30.07.11 10:31, Genes MailLists (lists@sapience.com) wrote:

> >> http://cafbit.com/entry/rapid_dhcp_or_how_do
> >
>
> Hmm ... the complaint of changing IP does not seem to make sense - as I
> read the article - the MAC simply remembers server info and instead of a
> blind dhcp (which causes delays if you are now on a new network as the
> dhcp server will not NAK a network for which is not authoritative), it
> ARP's the remembered server first which is very fast - hard to see how
> this would cause problems (shy of bugs of course)...

IIRC connman (i.e. NM's competition) can do the ARP magic, too.

Lennart

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Old 07-30-2011, 03:46 PM
Genes MailLists
 
Default Fwd: Rapid DHCP

On 07/30/2011 10:37 AM, Lennart Poettering wrote:
> On Sat, 30.07.11 10:31, Genes MailLists (lists@sapience.com) wrote:
>
>>>> http://cafbit.com/entry/rapid_dhcp_or_how_do
>>>

>
> IIRC connman (i.e. NM's competition) can do the ARP magic, too.
>
> Lennart
>


Seems like a pretty reasonable thing to do - surely better than just
waiting for a timeout to decide if the server is not there ... are you
aware of any gotcha's ?
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Old 07-30-2011, 10:49 PM
Dan Williams
 
Default Fwd: Rapid DHCP

On Sat, 2011-07-30 at 11:46 -0400, Genes MailLists wrote:
> On 07/30/2011 10:37 AM, Lennart Poettering wrote:
> > On Sat, 30.07.11 10:31, Genes MailLists (lists@sapience.com) wrote:
> >
> >>>> http://cafbit.com/entry/rapid_dhcp_or_how_do
> >>>
>
> >
> > IIRC connman (i.e. NM's competition) can do the ARP magic, too.
> >
> > Lennart
> >
>
>
> Seems like a pretty reasonable thing to do - surely better than just
> waiting for a timeout to decide if the server is not there ... are you
> aware of any gotcha's ?

NM already keeps DHCP information around based on the network you're
connecting to, so we don't need to ARP a bunch of servers just to
determine whether the DHCP server we wanted is still there. dhclient is
smart enough to attempt to reclaim the lease if it's not already
expired. Note that the Mac attempts to ARP a number of different DHCP
servers (192.168.2.1, 192.168.4.1, 192.168.1.1) which would be pointless
with NetworkManager, because it's extremely unlikely that the DHCP
server on your wifi network has changed; NM would simply know that the
last DHCP server used *on that wifi network* was 192.168.1.1 and not
bother to try talking to other ones like Mac OS X appears to do.

NM could use the same method of ARPing multiple DHCP servers that Mac OS
X does, but it wouldn't provide much additional benefit, if any, at
least on WiFi networks. It could be used on wired networks to (a)
determine which wired network you're connected to, and (b) do rapid
DHCP. Again, NM already knows what DHCP server and what lease was last
used on the specific wifi network you just connected to, and it won't
bother doing a DISCOVER, it'll just jump to RENEW if your lease is still
valid.

What's unique about the method described there is that the Mac
configures the interface with the same IP address it previously had if
the lease is still valid, while NetworkManager waits for the DHCP server
confirm the lease. So we could presumptuously configure the interface
with the previous address from the lease and then only tear it down if
the DHCP server fails or rejects the renewal.

Of course, none of this helps if your DHCP leases are short, but it
certainly helps if you put your laptop to sleep a lot and wake it up in
the same location.

Dan

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Old 07-30-2011, 11:41 PM
Nathaniel McCallum
 
Default Fwd: Rapid DHCP

Dan, that works on wireless networks. On wired networks the ARP technique determines *which* of the valid leases you should attempt to restore. So on a wired network you:

1. ARP the known DHCP server IPs to discover the subnet.

2. ARP the IP from the valid lease on that subnet to avoid collision.

3. Restore the ifconfig from the still valid lease.

4. Renew the lease.


This should be pretty sane and gives large speedups to resuming on wired (which people with docks do a lot).


Nathaniel

On Jul 30, 2011 6:45 PM, "Dan Williams" <dcbw@redhat.com> wrote:> On Sat, 2011-07-30 at 11:46 -0400, Genes MailLists wrote:

>> On 07/30/2011 10:37 AM, Lennart Poettering wrote:
>> > On Sat, 30.07.11 10:31, Genes MailLists (lists@sapience.com) wrote:
>> >
>> >>>> http://cafbit.com/entry/rapid_dhcp_or_how_do

>> >>>
>>
>> >
>> > IIRC connman (i.e. NM's competition) can do the ARP magic, too.
>> >
>> > Lennart
>> >
>>
>>

>> Seems like a pretty reasonable thing to do - surely better than just
>> waiting for a timeout to decide if the server is not there ... are you
>> aware of any gotcha's ?
>
> NM already keeps DHCP information around based on the network you're

> connecting to, so we don't need to ARP a bunch of servers just to
> determine whether the DHCP server we wanted is still there. dhclient is
> smart enough to attempt to reclaim the lease if it's not already

> expired. Note that the Mac attempts to ARP a number of different DHCP
> servers (192.168.2.1, 192.168.4.1, 192.168.1.1) which would be pointless
> with NetworkManager, because it's extremely unlikely that the DHCP

> server on your wifi network has changed; NM would simply know that the
> last DHCP server used *on that wifi network* was 192.168.1.1 and not
> bother to try talking to other ones like Mac OS X appears to do.

>
> NM could use the same method of ARPing multiple DHCP servers that Mac OS
> X does, but it wouldn't provide much additional benefit, if any, at
> least on WiFi networks. It could be used on wired networks to (a)

> determine which wired network you're connected to, and (b) do rapid
> DHCP. Again, NM already knows what DHCP server and what lease was last
> used on the specific wifi network you just connected to, and it won't

> bother doing a DISCOVER, it'll just jump to RENEW if your lease is still
> valid.
>
> What's unique about the method described there is that the Mac
> configures the interface with the same IP address it previously had if

> the lease is still valid, while NetworkManager waits for the DHCP server
> confirm the lease. So we could presumptuously configure the interface
> with the previous address from the lease and then only tear it down if

> the DHCP server fails or rejects the renewal.
>
> Of course, none of this helps if your DHCP leases are short, but it
> certainly helps if you put your laptop to sleep a lot and wake it up in
> the same location.

>
> Dan
>
> --
> devel mailing list
> devel@lists.fedoraproject.org
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Old 07-31-2011, 03:30 AM
Genes MailLists
 
Default Fwd: Rapid DHCP

On 07/30/2011 06:49 PM, Dan Williams wrote:

>
> NM already keeps DHCP information around based on the network you're
> connecting to, so we don't need to ARP a bunch of servers just to
> determine whether the DHCP server we wanted is still there. dhclient is

Cool - so is NM already pretty optimal for the case when one sleeps a
laptop - and wakes it up in a new wireless domain?

How does it know the dhcp server is still there when the laptop has
moved on?

> What's unique about the method described there is that the Mac
> configures the interface with the same IP address it previously had if
> the lease is still valid, while NetworkManager waits for the DHCP server
> confirm the lease. So we could presumptuously configure the interface
> with the previous address from the lease and then only tear it down if
> the DHCP server fails or rejects the renewal.

Probably best not to do this - as it can lead to duplicate IP's on the
network - even if briefly - wasn't something like this an issue with
some smartphones and princeton univ wifi - and led to them banning
android for whatever version had the problem ?

http://code.google.com/p/android/issues/detail?id=11236

>
> Of course, none of this helps if your DHCP leases are short, but it
> certainly helps if you put your laptop to sleep a lot and wake it up in
> the same location.
>

I tend to wake mine up in new locations a lot ... NM doesn't seem to
take very long to latch onto the new one.

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Old 07-31-2011, 04:35 AM
Chuck Anderson
 
Default Fwd: Rapid DHCP

On Sat, Jul 30, 2011 at 11:30:30PM -0400, Genes MailLists wrote:
> On 07/30/2011 06:49 PM, Dan Williams wrote:
> > What's unique about the method described there is that the Mac
> > configures the interface with the same IP address it previously had if
> > the lease is still valid, while NetworkManager waits for the DHCP server
> > confirm the lease. So we could presumptuously configure the interface
> > with the previous address from the lease and then only tear it down if
> > the DHCP server fails or rejects the renewal.
>
> Probably best not to do this - as it can lead to duplicate IP's on the
> network - even if briefly - wasn't something like this an issue with
> some smartphones and princeton univ wifi - and led to them banning
> android for whatever version had the problem ?

No, it cannot lead to duplicate IPs *if the lease is still valid*. If
the client has a cached lease, and the lease has not yet reached
expiry, then the promise that the DHCP server has made to that client
for it to use that IP address for that period of time is still valid
and the client is free to continue use that IP address.

> http://code.google.com/p/android/issues/detail?id=11236

This was a case of a client continuing to use an IP address /after it
had expired/. This is clearly broken behavior.

> > Of course, none of this helps if your DHCP leases are short, but it
> > certainly helps if you put your laptop to sleep a lot and wake it up in
> > the same location.
> >
>
> I tend to wake mine up in new locations a lot ... NM doesn't seem to
> take very long to latch onto the new one.

Most of the problems I have after resume are with flakey wireless
drivers and/or wpa_supplicant making a solid association to an AP
before even getting to the DHCP stage.
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Old 07-31-2011, 09:50 AM
David Woodhouse
 
Default Fwd: Rapid DHCP

On Sat, 2011-07-30 at 17:49 -0500, Dan Williams wrote:
> NM already keeps DHCP information around based on the network you're
> connecting to, so we don't need to ARP a bunch of servers just to
> determine whether the DHCP server we wanted is still there.

That's fine on wireless, but not so useful on wired.

But who cares? RA works nice and fast; it's only Legacy IP that's
slow...

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