kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

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kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Patrick O'Callaghan-2
I installed the above kernel this morning and immediately experienced
very noticeable delays in accessing websites (2 or 3 seconds each
time), apparently caused by slow DNS lookups. The same happened when
running a 'ping' from the Shell, so I don't think the browser (Chrome)
is to blame.

Rebooting with 4.13.4-200.fc26.x86_64 fixed the problem immediately.

Anyone else notice this?

poc
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Re: kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Ed Greshko
On 10/11/17 20:26, Patrick O'Callaghan wrote:
> I installed the above kernel this morning and immediately experienced
> very noticeable delays in accessing websites (2 or 3 seconds each
> time), apparently caused by slow DNS lookups. The same happened when
> running a 'ping' from the Shell, so I don't think the browser (Chrome)
> is to blame.
>
> Rebooting with 4.13.4-200.fc26.x86_64 fixed the problem immediately.
>
> Anyone else notice this?

Examples of the sites you've tried?  Whose DNS server are you using?   If your ISP,
can you change to 8.8.8.8 (google's servers)?

I'm not having any problem.

[egreshko@meimei ~]$ uname -r
4.13.5-200.fc26.x86_64

[egreshko@meimei ~]$ time host bbc.co.uk
bbc.co.uk has address 212.58.246.79
bbc.co.uk has address 212.58.244.23
bbc.co.uk has address 212.58.244.22
bbc.co.uk has address 212.58.246.78
bbc.co.uk has IPv6 address 2001:41c1:4008::bbc:1
bbc.co.uk has IPv6 address 2001:41c1:400c::bbc:1
bbc.co.uk has IPv6 address 2001:41c1:4008::bbc:2
bbc.co.uk has IPv6 address 2001:41c1:400c::bbc:2
bbc.co.uk has IPv6 address 2001:41c1:4008::bbc:3
bbc.co.uk has IPv6 address 2001:41c1:4008::bbc:4
bbc.co.uk has IPv6 address 2001:41c1:400c::bbc:4
bbc.co.uk has IPv6 address 2001:41c1:400c::bbc:3
bbc.co.uk mail is handled by 10 cluster1.eu.messagelabs.com.
bbc.co.uk mail is handled by 20 cluster1a.eu.messagelabs.com.

real    0m0.155s
user    0m0.008s
sys     0m0.002s

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Re: kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Patrick O'Callaghan-2
On Wed, 2017-10-11 at 21:24 +0800, Ed Greshko wrote:

> On 10/11/17 20:26, Patrick O'Callaghan wrote:
> > I installed the above kernel this morning and immediately experienced
> > very noticeable delays in accessing websites (2 or 3 seconds each
> > time), apparently caused by slow DNS lookups. The same happened when
> > running a 'ping' from the Shell, so I don't think the browser (Chrome)
> > is to blame.
> >
> > Rebooting with 4.13.4-200.fc26.x86_64 fixed the problem immediately.
> >
> > Anyone else notice this?
>
> Examples of the sites you've tried?  Whose DNS server are you using?   If your ISP,
> can you change to 8.8.8.8 (google's servers)?

Popular sites such as www.nytimes.com and www.theguardian.com. I took a
look at my router's config and saw that its DNS setting was set to
"dynamic". I assume that means uPnP or DHCP but I don't know where it
was pointing at. I changed it to 8.8.8.8 and 8.8.4.4 and rebooted the
new kernel. It seems to have improved but I'll keep an eye on it.

I don't see how a change of kernel could have affected this, unless
there's some subtlety in uPnP (or DHCP), but we'll see.

poc
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Re: kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Ed Greshko-2
On 10/12/17 00:48, Patrick O'Callaghan wrote:

> On Wed, 2017-10-11 at 21:24 +0800, Ed Greshko wrote:
>> On 10/11/17 20:26, Patrick O'Callaghan wrote:
>>> I installed the above kernel this morning and immediately experienced
>>> very noticeable delays in accessing websites (2 or 3 seconds each
>>> time), apparently caused by slow DNS lookups. The same happened when
>>> running a 'ping' from the Shell, so I don't think the browser (Chrome)
>>> is to blame.
>>>
>>> Rebooting with 4.13.4-200.fc26.x86_64 fixed the problem immediately.
>>>
>>> Anyone else notice this?
>> Examples of the sites you've tried?  Whose DNS server are you using?   If your ISP,
>> can you change to 8.8.8.8 (google's servers)?
> Popular sites such as www.nytimes.com and www.theguardian.com. I took a
> look at my router's config and saw that its DNS setting was set to
> "dynamic". I assume that means uPnP or DHCP but I don't know where it
> was pointing at. I changed it to 8.8.8.8 and 8.8.4.4 and rebooted the
> new kernel. It seems to have improved but I'll keep an eye on it.
Unless your router uses odd terminology Dynamic DNS, or DDNS, isn't what you think it is.

DDNS  is a way to register your router's IP address in the DNS if it changes. 
Meaning if your router gets its IP address via DHCP from your ISP DDNS will update
the DNS to reflect the change.  This way if you are outside your LAN you can always
use a name to get the IP address of your router and connect to it or (via port
forwarding) devices on your LAN even if the IP address of your router changes.

So, in your configuration it sounds like your Fedora system is getting all the
network configuration from your router.  So, if you look in /etc/resolv.conf you see
the IP address of your router?  Yes?

>
> I don't see how a change of kernel could have affected this, unless
> there's some subtlety in uPnP (or DHCP), but we'll see.
>
>
I don't think you're seeing any kernel issues.

Anyway, in my network I have various DNS configurations for different reasons.

I have a caching nameserver running on one system.  I have another system configured
to point to my router which uses a proxy DNS provided by my VPN service.  And another
system which is configured to directly contact Google's servers.

All are running just fine and queries all happen in milliseconds. 

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Re: kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Patrick O'Callaghan-2
On Thu, 2017-10-12 at 05:55 +0800, Ed Greshko wrote:

> On 10/12/17 00:48, Patrick O'Callaghan wrote:
> > On Wed, 2017-10-11 at 21:24 +0800, Ed Greshko wrote:
> > > On 10/11/17 20:26, Patrick O'Callaghan wrote:
> > > > I installed the above kernel this morning and immediately experienced
> > > > very noticeable delays in accessing websites (2 or 3 seconds each
> > > > time), apparently caused by slow DNS lookups. The same happened when
> > > > running a 'ping' from the Shell, so I don't think the browser (Chrome)
> > > > is to blame.
> > > >
> > > > Rebooting with 4.13.4-200.fc26.x86_64 fixed the problem immediately.
> > > >
> > > > Anyone else notice this?
> > >
> > > Examples of the sites you've tried?  Whose DNS server are you using?   If your ISP,
> > > can you change to 8.8.8.8 (google's servers)?
> >
> > Popular sites such as www.nytimes.com and www.theguardian.com. I took a
> > look at my router's config and saw that its DNS setting was set to
> > "dynamic". I assume that means uPnP or DHCP but I don't know where it
> > was pointing at. I changed it to 8.8.8.8 and 8.8.4.4 and rebooted the
> > new kernel. It seems to have improved but I'll keep an eye on it.
>
> Unless your router uses odd terminology Dynamic DNS, or DDNS, isn't what you think it is.
>
> DDNS  is a way to register your router's IP address in the DNS if it changes.
> Meaning if your router gets its IP address via DHCP from your ISP DDNS will update
> the DNS to reflect the change.  This way if you are outside your LAN you can always
> use a name to get the IP address of your router and connect to it or (via port
> forwarding) devices on your LAN even if the IP address of your router changes.

I know what DDNS is. That's not what I'm talking about. I'm not using
DDNS at present though I have done in the past. The router has a
control panel for configuring *its own* DNS resolver, i.e. where it
forwards queries to upstream. It was set to "dynamic", which I
interpret to mean "get the configuration from the ISP". (The broadband
connection is PPPoE so it presumably behaves like an Ethernet).
Changing it to explicitly point at Google is what had the desired
effect. It now seems likely that the kernel version was mere
coincidence, at least I hope so.

> So, in your configuration it sounds like your Fedora system is getting all the
> network configuration from your router.  So, if you look in /etc/resolv.conf you see
> the IP address of your router?  Yes?

Correct.

> >
> > I don't see how a change of kernel could have affected this, unless
> > there's some subtlety in uPnP (or DHCP), but we'll see.
> >
> >
>
> I don't think you're seeing any kernel issues.

As I say, that may well be the case (I hope it is). The router config
change seems to have corrected the problem for now.

poc
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Re: kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Ed Greshko
On 10/12/17 06:08, Patrick O'Callaghan wrote:
> I know what DDNS is. That's not what I'm talking about. I'm not using
> DDNS at present though I have done in the past. The router has a
> control panel for configuring *its own* DNS resolver, i.e. where it
> forwards queries to upstream. It was set to "dynamic", which I
> interpret to mean "get the configuration from the ISP". (The broadband
> connection is PPPoE so it presumably behaves like an Ethernet).
> Changing it to explicitly point at Google is what had the desired
> effect. It now seems likely that the kernel version was mere
> coincidence, at least I hope so.

It was 05:45 and still dark out.  Forgot who I was talking with.  Sorry about that.

>
>> So, in your configuration it sounds like your Fedora system is getting all the
>> network configuration from your router.  So, if you look in /etc/resolv.conf you see
>> the IP address of your router?  Yes?
> Correct.
>
>>> I don't see how a change of kernel could have affected this, unless
>>> there's some subtlety in uPnP (or DHCP), but we'll see.
>>>
>>>
>> I don't think you're seeing any kernel issues.
> As I say, that may well be the case (I hope it is). The router config
> change seems to have corrected the problem for now.

Would have been nice know what resolver the router was using when set to Dynamic.....


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Re: kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Patrick O'Callaghan-2
On Thu, 2017-10-12 at 07:08 +0800, Ed Greshko wrote:

> On 10/12/17 06:08, Patrick O'Callaghan wrote:
> > I know what DDNS is. That's not what I'm talking about. I'm not using
> > DDNS at present though I have done in the past. The router has a
> > control panel for configuring *its own* DNS resolver, i.e. where it
> > forwards queries to upstream. It was set to "dynamic", which I
> > interpret to mean "get the configuration from the ISP". (The broadband
> > connection is PPPoE so it presumably behaves like an Ethernet).
> > Changing it to explicitly point at Google is what had the desired
> > effect. It now seems likely that the kernel version was mere
> > coincidence, at least I hope so.
>
> It was 05:45 and still dark out.  Forgot who I was talking with.  Sorry about that.

No worries. Hope I didn't sound snappy, which wasn't my intention.

> > > So, in your configuration it sounds like your Fedora system is getting all the
> > > network configuration from your router.  So, if you look in /etc/resolv.conf you see
> > > the IP address of your router?  Yes?
> >
> > Correct.
> >
> > > > I don't see how a change of kernel could have affected this, unless
> > > > there's some subtlety in uPnP (or DHCP), but we'll see.
> > > >
> > > >
> > >
> > > I don't think you're seeing any kernel issues.
> >
> > As I say, that may well be the case (I hope it is). The router config
> > change seems to have corrected the problem for now.
>
>
> Would have been nice know what resolver the router was using when set to Dynamic.....

Probably the ISPs own server, but there's no easy way to know and by
this time they've probably corrected any problem they may have had.

poc
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Re: kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Ed Greshko-2
On 10/12/17 18:01, Patrick O'Callaghan wrote:

> On Thu, 2017-10-12 at 07:08 +0800, Ed Greshko wrote:
>> On 10/12/17 06:08, Patrick O'Callaghan wrote:
>>> I know what DDNS is. That's not what I'm talking about. I'm not using
>>> DDNS at present though I have done in the past. The router has a
>>> control panel for configuring *its own* DNS resolver, i.e. where it
>>> forwards queries to upstream. It was set to "dynamic", which I
>>> interpret to mean "get the configuration from the ISP". (The broadband
>>> connection is PPPoE so it presumably behaves like an Ethernet).
>>> Changing it to explicitly point at Google is what had the desired
>>> effect. It now seems likely that the kernel version was mere
>>> coincidence, at least I hope so.
>> It was 05:45 and still dark out.  Forgot who I was talking with.  Sorry about that.
> No worries. Hope I didn't sound snappy, which wasn't my intention.
Hah, hah.   I was more worried about my sounding condescending. 
 
>
> Probably the ISPs own server, but there's no easy way to know and by
> this time they've probably corrected any problem they may have had.
>

Yeah.  Oh, well....


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Re: kernel-4.13.5-200.fc26.x86_64 DNS slowdown?

Tim-163
In reply to this post by Patrick O'Callaghan-2
Ed Greshko:
>> Would have been nice know what resolver the router was using when
>> set to Dynamic.....

Patrick O'Callaghan:
> Probably the ISPs own server, but there's no easy way to know and by
> this time they've probably corrected any problem they may have had.

You can often telnet or ssh into routers, and issue commands or read
configs.

I gave up using my ISP's DNS servers years ago.  They were always on
the fritz, and impose censorship on you.

--
[tim@localhost ~]$ uname -rsvp
Linux 4.13.4-200.fc26.x86_64 #1 SMP Thu Sep 28 20:46:39 UTC 2017 x86_64

Boilerplate:  All mail to my mailbox is automatically deleted.
There is no point trying to privately email me, I only get to see
the messages posted to the mailing list.

Sorry, no viruses was included with this email, please read the rm
and fdisc man files to learn how to seriously mangle your own system.
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