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Re: DNS problems still
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Graham J
Jun 5, 2014, 9:32:15 AM6/5/14
to
Tim Streater wrote:
> Over the last day or so I'm getting intermittent what I suppose must be
> DNS issues. Safari will suddenly say it can't find twitter.com, as in
> "Safari can't open the page twitter.com because it can't find the
> server twitter.com". Then a few minutes later it'll be OK.
>
> Or it will decide it can't find news.bbc.co.uk while at the same time
> finding twitter, but none of twitter's images.
>
> When I looked in System Prefs -> Network -> Advanced -> DNS, all I
> found there was a greyed out entry to 192.168.0.1 - my router, which I
> assume means, in effect, use the DNS servers my router gets
> automatically from the ISP. When, a couple of weeks ago, I had the
> issue I describe, I wondered if it would help to add some DNS entries
> in System Prefs, so I've now got a couple of BT ones and a couple of
> Falcoda ones. But this doesn't seem to have helped.
>
> Any observations welcome.
>
Who is your ISP?
Is the problem always immediately resolved by rebooting your router?
Prepare a list of IP addresses that should always be available, and
check you can ping them as soon as you see the problem. Then find out
if the URLs that should point to these addresses can be resolved by
trying to ping by name.
For example:
Ping 212.23.8.6 - should always reply, but if
Ping ntp0.zen.co.uk - does not resolve to that address then you can
suspect the DNS lookup.
If ping 212.23.8.6 does not reply then try 212.23.10.129 (i.e.
ntp0.zen.co.uk). There are more zen time servers - but if more than one
doesn't respond then it is likely that you have some other connectivity
issue.
You could have these pings set up as a script (or whatever a Mac does to
automate things) so a single click can run a quick sequence of tests.
Adding extra DNS servers probably doesn't help. However if you see a
delay of up to 15 seconds in resolving addresses that may indicate that
the lookup on the first DNS server has failed and after whatever timeout
is present in the computer it will try the next. But total failure
indicates that none of the DNS servers responded.
Do you have another computer connected to the same router that you could
check the same URL? That might narrow down the problem to one partcular
computer ...
--
Graham J
> Over the last day or so I'm getting intermittent what I suppose must be
> DNS issues. Safari will suddenly say it can't find twitter.com, as in
> "Safari can't open the page twitter.com because it can't find the
> server twitter.com". Then a few minutes later it'll be OK.
>
> Or it will decide it can't find news.bbc.co.uk while at the same time
> finding twitter, but none of twitter's images.
>
> When I looked in System Prefs -> Network -> Advanced -> DNS, all I
> found there was a greyed out entry to 192.168.0.1 - my router, which I
> assume means, in effect, use the DNS servers my router gets
> automatically from the ISP. When, a couple of weeks ago, I had the
> issue I describe, I wondered if it would help to add some DNS entries
> in System Prefs, so I've now got a couple of BT ones and a couple of
> Falcoda ones. But this doesn't seem to have helped.
>
> Any observations welcome.
>
Who is your ISP?
Is the problem always immediately resolved by rebooting your router?
Prepare a list of IP addresses that should always be available, and
check you can ping them as soon as you see the problem. Then find out
if the URLs that should point to these addresses can be resolved by
trying to ping by name.
For example:
Ping 212.23.8.6 - should always reply, but if
Ping ntp0.zen.co.uk - does not resolve to that address then you can
suspect the DNS lookup.
If ping 212.23.8.6 does not reply then try 212.23.10.129 (i.e.
ntp0.zen.co.uk). There are more zen time servers - but if more than one
doesn't respond then it is likely that you have some other connectivity
issue.
You could have these pings set up as a script (or whatever a Mac does to
automate things) so a single click can run a quick sequence of tests.
Adding extra DNS servers probably doesn't help. However if you see a
delay of up to 15 seconds in resolving addresses that may indicate that
the lookup on the first DNS server has failed and after whatever timeout
is present in the computer it will try the next. But total failure
indicates that none of the DNS servers responded.
Do you have another computer connected to the same router that you could
check the same URL? That might narrow down the problem to one partcular
computer ...
--
Graham J
Graham J
Jun 5, 2014, 10:45:54 AM6/5/14
to
Graham J wrote:
[snip]
Typo ... ntp1 ...
Sorry.
--
Graham J
[snip]
Typo ... ntp1 ...
>
> If ping 212.23.8.6 does not reply then try 212.23.10.129 (i.e.
> ntp1.zen.co.uk).
> If ping 212.23.8.6 does not reply then try 212.23.10.129 (i.e.
Sorry.
--
Graham J
Message has been deleted
Graham J
Jun 5, 2014, 2:54:34 PM6/5/14
to
Tim Streater wrote:
[snip]
> OK - and when this is happening, the response is essentially straight
> away. I should check whether that occasions any network traffic.
Then it's probably not a DNS issue. If what you mean is that the
browser immediately says it can't find the website then it hasn't tried
a DNS lookup. This might be a fault in the browser.
Do you have another browser installed that you can try?
Can you ping the website by URL? If so, that would tend to confirm a
browser problem.
Or there might be a problem in the TCP/IP mechanism. If you ping a
known good IP address without success the networking might be an issue.
Can you ping your router?
--
Graham J
[snip]
> OK - and when this is happening, the response is essentially straight
> away. I should check whether that occasions any network traffic.
Then it's probably not a DNS issue. If what you mean is that the
browser immediately says it can't find the website then it hasn't tried
a DNS lookup. This might be a fault in the browser.
Do you have another browser installed that you can try?
Can you ping the website by URL? If so, that would tend to confirm a
browser problem.
Or there might be a problem in the TCP/IP mechanism. If you ping a
known good IP address without success the networking might be an issue.
Can you ping your router?
--
Graham J
Message has been deleted
Graham J
Jun 5, 2014, 5:19:45 PM6/5/14
to
Tim Streater wrote:
> In article <lmqedj$l9d$1...@dont-email.me>, Graham J <gra...@invalid.com>
>
> I have 5 browsers installed. Tried Firefox. Fail. Tried Chrome. Worked
> OK. Back to Safari and FF. Both still fail. Tried Opera. Worked. Back
> to Safari & FF. Worked there too - incident over.
>
> Didn't get a chance to try iCab or do anything else.
>
Beginning to suspect random failures of your internet connection.
Cn you leave a browser (possibly on another computer) continuously
monitoring your router? Perhaps also listening to internet radio so you
would know as soon as the connection failed ...?
--
Graham J
> In article <lmqedj$l9d$1...@dont-email.me>, Graham J <gra...@invalid.com>
> wrote:
>
>> Tim Streater wrote:
>> [snip]
>>
>> > OK - and when this is happening, the response is essentially straight
>> > away. I should check whether that occasions any network traffic.
>>
>> Then it's probably not a DNS issue. If what you mean is that the
>> browser immediately says it can't find the website then it hasn't
>> tried a DNS lookup. This might be a fault in the browser.
>>
>> Do you have another browser installed that you can try?
>
> Well it just happened again (twitter and another site, on Safari)
>
>> Tim Streater wrote:
>> [snip]
>>
>> > OK - and when this is happening, the response is essentially straight
>> > away. I should check whether that occasions any network traffic.
>>
>> Then it's probably not a DNS issue. If what you mean is that the
>> browser immediately says it can't find the website then it hasn't
>> tried a DNS lookup. This might be a fault in the browser.
>>
>> Do you have another browser installed that you can try?
>
>
> I have 5 browsers installed. Tried Firefox. Fail. Tried Chrome. Worked
> OK. Back to Safari and FF. Both still fail. Tried Opera. Worked. Back
> to Safari & FF. Worked there too - incident over.
>
> Didn't get a chance to try iCab or do anything else.
>
Beginning to suspect random failures of your internet connection.
Cn you leave a browser (possibly on another computer) continuously
monitoring your router? Perhaps also listening to internet radio so you
would know as soon as the connection failed ...?
--
Graham J
ray
Jun 6, 2014, 4:40:50 AM6/6/14
to
Tim Streater <timst...@greenbee.net> wrote:
> In article <lmqedj$l9d$1...@dont-email.me>, Graham J <gra...@invalid.com>
> wrote:
>
> In article <lmqedj$l9d$1...@dont-email.me>, Graham J <gra...@invalid.com>
> wrote:
>
>> Tim Streater wrote:
>> [snip]
>>>> OK - and when this is happening, the response is essentially straight
>>> away. I should check whether that occasions any network traffic.
>>> Then it's probably not a DNS issue. If what you mean is that the >
>>> browser immediately says it can't find the website then it hasn't tried
>>> > a DNS lookup. This might be a fault in the browser.
>>> Do you have another browser installed that you can try?
>
>> [snip]
>>>> OK - and when this is happening, the response is essentially straight
>>> away. I should check whether that occasions any network traffic.
>>> Then it's probably not a DNS issue. If what you mean is that the >
>>> browser immediately says it can't find the website then it hasn't tried
>>> > a DNS lookup. This might be a fault in the browser.
>>> Do you have another browser installed that you can try?
>
> Well it just happened again (twitter and another site, on Safari)
>
> I have 5 browsers installed. Tried Firefox. Fail. Tried Chrome. Worked
> OK. Back to Safari and FF. Both still fail. Tried Opera. Worked. Back
> to Safari & FF. Worked there too - incident over.
>
> Didn't get a chance to try iCab or do anything else.
Do you have Little Snitch installed?
>
> I have 5 browsers installed. Tried Firefox. Fail. Tried Chrome. Worked
> OK. Back to Safari and FF. Both still fail. Tried Opera. Worked. Back
> to Safari & FF. Worked there too - incident over.
>
> Didn't get a chance to try iCab or do anything else.
I had a similar problem yesterday on the Mini, where every other computer
and iThing in the house worked fine. As Di the Mini earlier in the week.
Switching off Little Snitch fixed it. I haven't had a chance to investigate
why yet.
--
"Gods are fragile things; they may be killed by a whiff of science or a
dose of common sense." -Chapman Cohen, author & lecturer (1868-1954)
Message has been deleted
Sak Wathanasin
Jun 6, 2014, 9:48:24 AM6/6/14
to
On Thursday, 5 June 2014 21:58:00 UTC+1, Tim Streater wrote:
> Didn't get a chance to try iCab or do anything else.
Try flushing the DNS cache:
> Didn't get a chance to try iCab or do anything else.
sudo dscacheutil -flushcache
Message has been deleted
Paul Sture
Jun 12, 2014, 7:30:52 AM6/12/14
to
On 2014-06-05, Tim Streater <timst...@greenbee.net> wrote:
> Last year I was seeing even odder things: Safari taking for ever (or
> failing) to load a page. Examination showed that the page source was
> there, what was missing was the extra resources (CSS files, images,
> ...). That seemed to get fixed which I put down to getting a new
> .version of Safari,
2 or 3 years ago I was regularly having problems with Safari. It was as
if a buffer wasn't being flushed somewhere. I could normally go to the
same URL with Firefox or Opera and get instant results so put it down to
Safari itself.
I switched to using Firefox as my main browser as a result.
>> Prepare a list of IP addresses that should always be available, and
>> check you can ping them as soon as you see the problem. Then find out
>> if the URLs that should point to these addresses can be resolved by
>> trying to ping by name.
>>
>> For example:
>>
>> Ping 212.23.8.6 - should always reply, but if
>> Ping ntp0.zen.co.uk - does not resolve to that address then you can
>> suspect the DNS lookup.
>>
>> If ping 212.23.8.6 does not reply then try 212.23.10.129 (i.e.
>> ntp0.zen.co.uk). There are more zen time servers - but if more than one
>> doesn't respond then it is likely that you have some other connectivity
>> issue.
>>
>> You could have these pings set up as a script (or whatever a Mac does to
>> automate things) so a single click can run a quick sequence of tests.
>
> Yes, I can do this easily enough.
I am currently out in the sticks and have to put up with a shared setup
via a homeplug. This is the script I have to test if I can reach the
router sitting at the other end of the homeplug circuit:
#!/bin/bash
date
ping -c 6 192.168.1.1
The date command in there is useful as a means of seeing when I last ran it.
>> Adding extra DNS servers probably doesn't help. However if you see a
>> delay of up to 15 seconds in resolving addresses that may indicate that
>> the lookup on the first DNS server has failed and after whatever timeout
>> is present in the computer it will try the next. But total failure
>> indicates that none of the DNS servers responded.
>
than you want, so let's look at the short form:
dig +short ntp0.zen.co.uk
212.23.8.6
and you can specify which DNS server to use via @
e.g.
dig +short @8.8.8.8 ntp0.zen.co.uk
212.23.8.6
where 8.8.8.8 is one of Google's DNS servers, which should be reachable
from anywhere.
>> Do you have another computer connected to the same router that you could
>> check the same URL? That might narrow down the problem to one partcular
>> computer ...
>
> Yeah, SWMBO's Mini.
>
> I should also try host when these failures occur.
>
--
You can't look at a glass as half full or half empty if it's overflowing.
> Last year I was seeing even odder things: Safari taking for ever (or
> failing) to load a page. Examination showed that the page source was
> there, what was missing was the extra resources (CSS files, images,
> ...). That seemed to get fixed which I put down to getting a new
> .version of Safari,
2 or 3 years ago I was regularly having problems with Safari. It was as
if a buffer wasn't being flushed somewhere. I could normally go to the
same URL with Firefox or Opera and get instant results so put it down to
Safari itself.
I switched to using Firefox as my main browser as a result.
>> Prepare a list of IP addresses that should always be available, and
>> check you can ping them as soon as you see the problem. Then find out
>> if the URLs that should point to these addresses can be resolved by
>> trying to ping by name.
>>
>> For example:
>>
>> Ping 212.23.8.6 - should always reply, but if
>> Ping ntp0.zen.co.uk - does not resolve to that address then you can
>> suspect the DNS lookup.
>>
>> If ping 212.23.8.6 does not reply then try 212.23.10.129 (i.e.
>> ntp0.zen.co.uk). There are more zen time servers - but if more than one
>> doesn't respond then it is likely that you have some other connectivity
>> issue.
>>
>> You could have these pings set up as a script (or whatever a Mac does to
>> automate things) so a single click can run a quick sequence of tests.
>
I am currently out in the sticks and have to put up with a shared setup
via a homeplug. This is the script I have to test if I can reach the
router sitting at the other end of the homeplug circuit:
#!/bin/bash
date
ping -c 6 192.168.1.1
The date command in there is useful as a means of seeing when I last ran it.
>> Adding extra DNS servers probably doesn't help. However if you see a
>> delay of up to 15 seconds in resolving addresses that may indicate that
>> the lookup on the first DNS server has failed and after whatever timeout
>> is present in the computer it will try the next. But total failure
>> indicates that none of the DNS servers responded.
>
> OK - and when this is happening, the response is essentially straight
> away. I should check whether that occasions any network traffic.
The dig command can be useful here. By default it spews probably more
> away. I should check whether that occasions any network traffic.
than you want, so let's look at the short form:
dig +short ntp0.zen.co.uk
212.23.8.6
and you can specify which DNS server to use via @
e.g.
dig +short @8.8.8.8 ntp0.zen.co.uk
212.23.8.6
where 8.8.8.8 is one of Google's DNS servers, which should be reachable
from anywhere.
>> Do you have another computer connected to the same router that you could
>> check the same URL? That might narrow down the problem to one partcular
>> computer ...
>
>
> I should also try host when these failures occur.
>
--
You can't look at a glass as half full or half empty if it's overflowing.
Paul Sture
Jun 12, 2014, 7:43:31 AM6/12/14
to
On 2014-06-05, Graham J <gra...@invalid.com> wrote:
> Tim Streater wrote:
>> In article <lmqedj$l9d$1...@dont-email.me>, Graham J <gra...@invalid.com>
>> wrote:
>>
>>> Tim Streater wrote:
>>> [snip]
>>>
>>> > OK - and when this is happening, the response is essentially straight
>>> > away. I should check whether that occasions any network traffic.
>>>
>>> Then it's probably not a DNS issue. If what you mean is that the
>>> browser immediately says it can't find the website then it hasn't
>>> tried a DNS lookup. This might be a fault in the browser.
Back in the Panther/Tiger era, someone told me that OS X only looks at the
> Tim Streater wrote:
>> In article <lmqedj$l9d$1...@dont-email.me>, Graham J <gra...@invalid.com>
>> wrote:
>>
>>> Tim Streater wrote:
>>> [snip]
>>>
>>> > OK - and when this is happening, the response is essentially straight
>>> > away. I should check whether that occasions any network traffic.
>>>
>>> Then it's probably not a DNS issue. If what you mean is that the
>>> browser immediately says it can't find the website then it hasn't
>>> tried a DNS lookup. This might be a fault in the browser.
first two DNS entries. I honestly don't know whether this is still the case
or not.
>>> Do you have another browser installed that you can try?
>>
>> Well it just happened again (twitter and another site, on Safari)
>>
>> I have 5 browsers installed. Tried Firefox. Fail. Tried Chrome. Worked
>> OK. Back to Safari and FF. Both still fail. Tried Opera. Worked. Back
>> to Safari & FF. Worked there too - incident over.
>>
>> Didn't get a chance to try iCab or do anything else.
>>
>
> Beginning to suspect random failures of your internet connection.
>
> Cn you leave a browser (possibly on another computer) continuously
> monitoring your router? Perhaps also listening to internet radio so you
> would know as soon as the connection failed ...?
connection goes AWOL for while. "For a while" in this context is usually
between a few seconds and a few minutes, but sometimes it persists for much
longer (resetting the homeplugs at both ends usually works). The glitch
can be short enough that internet radio isn't affected because it's buffered.
Sometimes, after a DNS failure Safari will simply repeat the error without
bothering to do a lookup again. The refresh button stubbornly refuses
to refresh, but killing that Safari tab and trying again in a new one
will persuade it to try again.
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