subject:"End\-user troubleshooting of bad c\-ares interaction with router"

Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-23 Thread Brad House via c-ares

Just glanced at the issue, looks like you summarized it well.

On 1/23/24 12:58 PM, Nicholas Chammas wrote:
To close the loop on this discussion, I’ve filed the following issue
with the gRPC folks:

https://github.com/grpc/grpc/issues/35638

Thank you again for all of your help. I would not have been able to
understand what’s going on without it.

On Jan 23, 2024, at 11:43 AM, Brad House wrote:

Yeah, it does clearly show them enqueuing IPv4 and IPv6 requests
separately. So either they need to add logic similar to c-ares has
internally with https://github.com/c-ares/c-ares/pull/551 or just use
ares_getaddrinfo() instead of ares_gethostbyname() with address
family AF_UNSPEC and let c-ares do the right thing.

On 1/23/24 11:25 AM, Nicholas Chammas wrote:

Thank you for all the troubleshooting help, Brad.

I am using gRPC via Apache Spark Connect (a Python library), so I am
two levels removed from c-ares itself. Looking in the Python virtual
environment where gRPC is installed, I’m not sure what file to run
otool on. The only seemingly relevant file I could find is
called cygrpc.cpython-311-darwin.so, and otool didn’t turn up
anything interesting on it.

I will take this issue up with the gRPC folks.

I see in several places that the gRPC folks are using
ares_gethostbyname:

*
https://github.com/grpc/grpc/blob/v1.60.0/src/core/lib/event_engine/ares_resolver.cc#L287-L293
*
https://github.com/grpc/grpc/blob/v1.60.0/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc#L748-L758
*
https://github.com/grpc/grpc/blob/v1.60.0/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc#L1075-L1086

On Jan 22, 2024, at 1:39 PM, Brad House wrote:

Are you using gRPC installed via homebrew or is it bundled with
something else? Usually package maintainers like homebrew will
dynamically link to the system versions of dependencies so they can
be updated independently. You might be able to run otool -L on
grpc to see what c-ares library its picking up (and if none are
listed, it might be compiled in statically).

That said, according to your grpc logs, it appears that grpc may be
itself performing both A and queries and expect responses to
both of those. I see the "A" reply comes back but the "" reply
never comes and it bails at that point. Many years ago c-ares
didn't have a way to request both A and records with one
query, but does these days via ares_getaddrinfo(), and it was
recently enhanced with logic to assist in the exact scenario you
are seeing, basically it will stop retrying when at least one
address family is returned.

You might need to escalate this to the gRPC folks.

On 1/22/24 12:10 PM, Nicholas Chammas wrote:
Here’s the output of adig and ahost
,
both with and without the DNS servers set directly on the network
interface (vs. just on the router).

I also learned that gRPC 1.60.0 may be using c-ares 1.19.1
,
though again that’s just via looking at the gRPC source and not
via some runtime query.

On Jan 21, 2024, at 7:34 AM, Brad House wrote:

I think homebrew distributes the 'adig' and 'ahost' utilities
from c-ares. Can you try using those to do the same lookup so we
can see the results?

On 1/19/24 11:01 AM, Nicholas Chammas wrote:

On Jan 17, 2024, at 3:38 PM, Brad House
wrote:

What version of c-ares is installed?

Sorry about the delay in responding. Answering this question is
more difficult than I expected.

I know that Spark Connect is running gRPC 1.160.0. Looking
through the gRPC repo, I see mention of c-ares 1.13.0
,
but I don’t know how that translates to my runtime. Homebrew
tells me I have c-ares 1.25.0 installed, but again, I’m not sure
if that’s what I’m actually running.

Is there a way I can directly query the version of c-ares being
run via Spark Connect / gRPC? I asked this question on the gRPC
forum but no
response yet.

For the record, I know that c-ares is involved because if I tell
gRPC to not use it (via GRPC_DNS_RESOLVER=native
)
then my problem disappears.

What DNS servers are configured on your MacOS system when its
not operating properly? The output of "scutil --dns" would be
helpful here.

Here’s that output.
I
believe 192.168.1.1 is just my local router, and on there is
where I have the default DNS servers set to 1.1.1.1 and 1.0.0.1.

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Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-23 Thread Nicholas Chammas via c-ares

To close the loop on this discussion, I’ve filed the following issue with the 
gRPC folks:

https://github.com/grpc/grpc/issues/35638

Thank you again for all of your help. I would not have been able to understand 
what’s going on without it.


> On Jan 23, 2024, at 11:43 AM, Brad House  wrote:
> 
> Yeah, it does clearly show them enqueuing IPv4 and IPv6 requests separately.  
> So either they need to add logic similar to c-ares has internally with 
> https://github.com/c-ares/c-ares/pull/551 or just use ares_getaddrinfo() 
> instead of ares_gethostbyname() with address family AF_UNSPEC and let c-ares 
> do the right thing.
> 
> 
> 
> On 1/23/24 11:25 AM, Nicholas Chammas wrote:
>> Thank you for all the troubleshooting help, Brad.
>> 
>> I am using gRPC via Apache Spark Connect (a Python library), so I am two 
>> levels removed from c-ares itself. Looking in the Python virtual environment 
>> where gRPC is installed, I’m not sure what file to run otool on. The only 
>> seemingly relevant file I could find is called cygrpc.cpython-311-darwin.so, 
>> and otool didn’t turn up anything interesting on it.
>> 
>> I will take this issue up with the gRPC folks.
>> 
>> I see in several places that the gRPC folks are using ares_gethostbyname:
>> https://github.com/grpc/grpc/blob/v1.60.0/src/core/lib/event_engine/ares_resolver.cc#L287-L293
>> https://github.com/grpc/grpc/blob/v1.60.0/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc#L748-L758
>> https://github.com/grpc/grpc/blob/v1.60.0/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc#L1075-L1086
>> 
>> 
>>> On Jan 22, 2024, at 1:39 PM, Brad House  
>>>  wrote:
>>> 
>>> Are you using gRPC installed via homebrew or is it bundled with something 
>>> else?  Usually package maintainers like homebrew will dynamically link to 
>>> the system versions of dependencies so they can be updated independently.  
>>> You might be able to run otool -L on grpc to see what c-ares library its 
>>> picking up (and if none are listed, it might be compiled in statically).
>>> 
>>> That said, according to your grpc logs, it appears that grpc may be itself 
>>> performing both A and  queries and expect responses to both of those.  
>>> I see the "A" reply comes back but the "" reply never comes and it 
>>> bails at that point.  Many years ago c-ares didn't have a way to request 
>>> both A and  records with one query, but does these days via 
>>> ares_getaddrinfo(), and it was recently enhanced with logic to assist in 
>>> the exact scenario you are seeing, basically it will stop retrying when at 
>>> least one address family is returned. 
>>> 
>>> You might need to escalate this to the gRPC folks.
>>> 
>>> On 1/22/24 12:10 PM, Nicholas Chammas wrote:
 Here’s the output of adig and ahost 
 ,
  both with and without the DNS servers set directly on the network 
 interface (vs. just on the router).
 
 I also learned that gRPC 1.60.0 may be using c-ares 1.19.1 
 , though 
 again that’s just via looking at the gRPC source and not via some runtime 
 query.
 
 
> On Jan 21, 2024, at 7:34 AM, Brad House  
>  wrote:
> 
> I think homebrew distributes the 'adig' and 'ahost' utilities from 
> c-ares.  Can you try using those to do the same lookup so we can see the 
> results?
> 
> On 1/19/24 11:01 AM, Nicholas Chammas wrote:
>> 
>>> On Jan 17, 2024, at 3:38 PM, Brad House  
>>>  wrote:
>>> What version of c-ares is installed?
>>> 
>> Sorry about the delay in responding. Answering this question is more 
>> difficult than I expected.
>> 
>> I know that Spark Connect is running gRPC 1.160.0. Looking through the 
>> gRPC repo, I see mention of c-ares 1.13.0 
>> , but I 
>> don’t know how that translates to my runtime. Homebrew tells me I have 
>> c-ares 1.25.0 installed, but again, I’m not sure if that’s what I’m 
>> actually running.
>> 
>> Is there a way I can directly query the version of c-ares being run via 
>> Spark Connect / gRPC? I asked this question on the gRPC forum 
>>  but no response yet.
>> 
>> For the record, I know that c-ares is involved because if I tell gRPC to 
>> not use it (via GRPC_DNS_RESOLVER=native 
>> )
>>  then my problem disappears.
>>> What DNS servers are configured on your MacOS system when its not 
>>> operating properly?  The output of "scutil --dns" would be helpful here.
>>> 
>>

Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-23 Thread Brad House via c-ares

Yeah, it does clearly show them enqueuing IPv4 and IPv6 requests
separately. So either they need to add logic similar to c-ares has
internally with https://github.com/c-ares/c-ares/pull/551 or just use
ares_getaddrinfo() instead of ares_gethostbyname() with address family
AF_UNSPEC and let c-ares do the right thing.

On 1/23/24 11:25 AM, Nicholas Chammas wrote:

Thank you for all the troubleshooting help, Brad.

I will take this issue up with the gRPC folks.

I see in several places that the gRPC folks are using ares_gethostbyname:

On Jan 22, 2024, at 1:39 PM, Brad House wrote:

Are you using gRPC installed via homebrew or is it bundled with
something else? Usually package maintainers like homebrew will
dynamically link to the system versions of dependencies so they can
be updated independently. You might be able to run otool -L on grpc
to see what c-ares library its picking up (and if none are listed, it
might be compiled in statically).

That said, according to your grpc logs, it appears that grpc may be
itself performing both A and queries and expect responses to
both of those. I see the "A" reply comes back but the "" reply
never comes and it bails at that point. Many years ago c-ares didn't
have a way to request both A and records with one query, but
does these days via ares_getaddrinfo(), and it was recently enhanced
with logic to assist in the exact scenario you are seeing, basically
it will stop retrying when at least one address family is returned.

You might need to escalate this to the gRPC folks.

On 1/22/24 12:10 PM, Nicholas Chammas wrote:
Here’s the output of adig and ahost
,
both with and without the DNS servers set directly on the network
interface (vs. just on the router).

I also learned that gRPC 1.60.0 may be using c-ares 1.19.1
,
though again that’s just via looking at the gRPC source and not via
some runtime query.

On Jan 21, 2024, at 7:34 AM, Brad House wrote:

I think homebrew distributes the 'adig' and 'ahost' utilities from
c-ares. Can you try using those to do the same lookup so we can
see the results?

On 1/19/24 11:01 AM, Nicholas Chammas wrote:

On Jan 17, 2024, at 3:38 PM, Brad House wrote:

What version of c-ares is installed?

Sorry about the delay in responding. Answering this question is
more difficult than I expected.

I know that Spark Connect is running gRPC 1.160.0. Looking through
the gRPC repo, I see mention of c-ares 1.13.0
,
but I don’t know how that translates to my runtime. Homebrew tells
me I have c-ares 1.25.0 installed, but again, I’m not sure if
that’s what I’m actually running.

Is there a way I can directly query the version of c-ares being
run via Spark Connect / gRPC? I asked this question on the gRPC
forum but no
response yet.

For the record, I know that c-ares is involved because if I tell
gRPC to not use it (via GRPC_DNS_RESOLVER=native
)
then my problem disappears.

What DNS servers are configured on your MacOS system when its not
operating properly? The output of "scutil --dns" would be
helpful here.

Here’s that output.
I
believe 192.168.1.1 is just my local router, and on there is where
I have the default DNS servers set to 1.1.1.1 and 1.0.0.1.

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Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-23 Thread Nicholas Chammas via c-ares

Thank you for all the troubleshooting help, Brad.

I am using gRPC via Apache Spark Connect (a Python library), so I am two levels 
removed from c-ares itself. Looking in the Python virtual environment where 
gRPC is installed, I’m not sure what file to run otool on. The only seemingly 
relevant file I could find is called cygrpc.cpython-311-darwin.so, and otool 
didn’t turn up anything interesting on it.

I will take this issue up with the gRPC folks.

I see in several places that the gRPC folks are using ares_gethostbyname:
https://github.com/grpc/grpc/blob/v1.60.0/src/core/lib/event_engine/ares_resolver.cc#L287-L293
https://github.com/grpc/grpc/blob/v1.60.0/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc#L748-L758
https://github.com/grpc/grpc/blob/v1.60.0/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.cc#L1075-L1086


> On Jan 22, 2024, at 1:39 PM, Brad House  wrote:
> 
> Are you using gRPC installed via homebrew or is it bundled with something 
> else?  Usually package maintainers like homebrew will dynamically link to the 
> system versions of dependencies so they can be updated independently.  You 
> might be able to run otool -L on grpc to see what c-ares library its picking 
> up (and if none are listed, it might be compiled in statically).
> 
> That said, according to your grpc logs, it appears that grpc may be itself 
> performing both A and  queries and expect responses to both of those.  I 
> see the "A" reply comes back but the "" reply never comes and it bails at 
> that point.  Many years ago c-ares didn't have a way to request both A and 
>  records with one query, but does these days via ares_getaddrinfo(), and 
> it was recently enhanced with logic to assist in the exact scenario you are 
> seeing, basically it will stop retrying when at least one address family is 
> returned. 
> 
> You might need to escalate this to the gRPC folks.
> 
> On 1/22/24 12:10 PM, Nicholas Chammas wrote:
>> Here’s the output of adig and ahost 
>> ,
>>  both with and without the DNS servers set directly on the network interface 
>> (vs. just on the router).
>> 
>> I also learned that gRPC 1.60.0 may be using c-ares 1.19.1 
>> , though again 
>> that’s just via looking at the gRPC source and not via some runtime query.
>> 
>> 
>>> On Jan 21, 2024, at 7:34 AM, Brad House  
>>>  wrote:
>>> 
>>> I think homebrew distributes the 'adig' and 'ahost' utilities from c-ares.  
>>> Can you try using those to do the same lookup so we can see the results?
>>> 
>>> On 1/19/24 11:01 AM, Nicholas Chammas wrote:
 
> On Jan 17, 2024, at 3:38 PM, Brad House  
>  wrote:
> What version of c-ares is installed?
> 
 Sorry about the delay in responding. Answering this question is more 
 difficult than I expected.
 
 I know that Spark Connect is running gRPC 1.160.0. Looking through the 
 gRPC repo, I see mention of c-ares 1.13.0 
 , but I 
 don’t know how that translates to my runtime. Homebrew tells me I have 
 c-ares 1.25.0 installed, but again, I’m not sure if that’s what I’m 
 actually running.
 
 Is there a way I can directly query the version of c-ares being run via 
 Spark Connect / gRPC? I asked this question on the gRPC forum 
  but no response yet.
 
 For the record, I know that c-ares is involved because if I tell gRPC to 
 not use it (via GRPC_DNS_RESOLVER=native 
 )
  then my problem disappears.
> What DNS servers are configured on your MacOS system when its not 
> operating properly?  The output of "scutil --dns" would be helpful here.
> 
 Here’s that output. 
 
  I believe 192.168.1.1 is just my local router, and on there is where I 
 have the default DNS servers set to 1.1.1.1 and 1.0.0.1.
 
>> 

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Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-22 Thread Brad House via c-ares

Are you using gRPC installed via homebrew or is it bundled with 
something else?  Usually package maintainers like homebrew will 
dynamically link to the system versions of dependencies so they can be 
updated independently.  You might be able to run otool -L on grpc to see 
what c-ares library its picking up (and if none are listed, it might be 
compiled in statically).


That said, according to your grpc logs, it appears that grpc may be 
itself performing both A and  queries and expect responses to both 
of those.  I see the "A" reply comes back but the "" reply never 
comes and it bails at that point.  Many years ago c-ares didn't have a 
way to request both A and  records with one query, but does these 
days via ares_getaddrinfo(), and it was recently enhanced with logic to 
assist in the exact scenario you are seeing, basically it will stop 
retrying when at least one address family is returned.


You might need to escalate this to the gRPC folks.

On 1/22/24 12:10 PM, Nicholas Chammas wrote:
Here’s the output of adig and ahost 
, 
both with and without the DNS servers set directly on the network 
interface (vs. just on the router).


I also learned that gRPC 1.60.0 may be using c-ares 1.19.1 
, though 
again that’s just via looking at the gRPC source and not via some 
runtime query.




On Jan 21, 2024, at 7:34 AM, Brad House  wrote:

I think homebrew distributes the 'adig' and 'ahost' utilities from 
c-ares.  Can you try using those to do the same lookup so we can see 
the results?


On 1/19/24 11:01 AM, Nicholas Chammas wrote:



On Jan 17, 2024, at 3:38 PM, Brad House  wrote:

What version of c-ares is installed?

Sorry about the delay in responding. Answering this question is more 
difficult than I expected.


I know that Spark Connect is running gRPC 1.160.0. Looking through 
the gRPC repo, I see mention of c-ares 1.13.0 
, 
but I don’t know how that translates to my runtime. Homebrew tells 
me I have c-ares 1.25.0 installed, but again, I’m not sure if that’s 
what I’m actually running.


Is there a way I can directly query the version of c-ares being run 
via Spark Connect / gRPC? I asked this question on the gRPC forum 
 but no response yet.


For the record, I know that c-ares is involved because if I tell 
gRPC to not use it (via GRPC_DNS_RESOLVER=native 
) 
then my problem disappears.


What DNS servers are configured on your MacOS system when its not 
operating properly?  The output of "scutil --dns" would be helpful 
here.


Here’s that output. 
 I 
believe 192.168.1.1 is just my local router, and on there is where I 
have the default DNS servers set to 1.1.1.1 and 1.0.0.1.


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Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-22 Thread Nicholas Chammas via c-ares

Here’s the output of adig and ahost 
,
 both with and without the DNS servers set directly on the network interface 
(vs. just on the router).

I also learned that gRPC 1.60.0 may be using c-ares 1.19.1 
, though again 
that’s just via looking at the gRPC source and not via some runtime query.


> On Jan 21, 2024, at 7:34 AM, Brad House  wrote:
> 
> I think homebrew distributes the 'adig' and 'ahost' utilities from c-ares.  
> Can you try using those to do the same lookup so we can see the results?
> 
> On 1/19/24 11:01 AM, Nicholas Chammas wrote:
>> 
>>> On Jan 17, 2024, at 3:38 PM, Brad House  
>>>  wrote:
>>> What version of c-ares is installed?
>>> 
>> Sorry about the delay in responding. Answering this question is more 
>> difficult than I expected.
>> 
>> I know that Spark Connect is running gRPC 1.160.0. Looking through the gRPC 
>> repo, I see mention of c-ares 1.13.0 
>> , but I 
>> don’t know how that translates to my runtime. Homebrew tells me I have 
>> c-ares 1.25.0 installed, but again, I’m not sure if that’s what I’m actually 
>> running.
>> 
>> Is there a way I can directly query the version of c-ares being run via 
>> Spark Connect / gRPC? I asked this question on the gRPC forum 
>>  but no response yet.
>> 
>> For the record, I know that c-ares is involved because if I tell gRPC to not 
>> use it (via GRPC_DNS_RESOLVER=native 
>> )
>>  then my problem disappears.
>>> What DNS servers are configured on your MacOS system when its not operating 
>>> properly?  The output of "scutil --dns" would be helpful here.
>>> 
>> Here’s that output. 
>> 
>>  I believe 192.168.1.1 is just my local router, and on there is where I have 
>> the default DNS servers set to 1.1.1.1 and 1.0.0.1.
>> 

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Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-21 Thread Brad House via c-ares

I think homebrew distributes the 'adig' and 'ahost' utilities from 
c-ares.  Can you try using those to do the same lookup so we can see the 
results?


On 1/19/24 11:01 AM, Nicholas Chammas wrote:



On Jan 17, 2024, at 3:38 PM, Brad House  wrote:

What version of c-ares is installed?

Sorry about the delay in responding. Answering this question is more 
difficult than I expected.


I know that Spark Connect is running gRPC 1.160.0. Looking through the 
gRPC repo, I see mention of c-ares 1.13.0 
, but 
I don’t know how that translates to my runtime. Homebrew tells me I 
have c-ares 1.25.0 installed, but again, I’m not sure if that’s what 
I’m actually running.


Is there a way I can directly query the version of c-ares being run 
via Spark Connect / gRPC? I asked this question on the gRPC forum 
 but no response yet.


For the record, I know that c-ares is involved because if I tell gRPC 
to not use it (via GRPC_DNS_RESOLVER=native 
) 
then my problem disappears.


What DNS servers are configured on your MacOS system when its not 
operating properly?  The output of "scutil --dns" would be helpful here.


Here’s that output. 
 I 
believe 192.168.1.1 is just my local router, and on there is where I 
have the default DNS servers set to 1.1.1.1 and 1.0.0.1.
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Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-19 Thread Nicholas Chammas via c-ares

> On Jan 17, 2024, at 3:38 PM, Brad House  wrote:
> What version of c-ares is installed?
> 
Sorry about the delay in responding. Answering this question is more difficult 
than I expected.

I know that Spark Connect is running gRPC 1.160.0. Looking through the gRPC 
repo, I see mention of c-ares 1.13.0 
, but I don’t 
know how that translates to my runtime. Homebrew tells me I have c-ares 1.25.0 
installed, but again, I’m not sure if that’s what I’m actually running.

Is there a way I can directly query the version of c-ares being run via Spark 
Connect / gRPC? I asked this question on the gRPC forum 
 but no response yet.

For the record, I know that c-ares is involved because if I tell gRPC to not 
use it (via GRPC_DNS_RESOLVER=native 
)
 then my problem disappears.
> What DNS servers are configured on your MacOS system when its not operating 
> properly?  The output of "scutil --dns" would be helpful here.
> 
Here’s that output. 

 I believe 192.168.1.1 is just my local router, and on there is where I have 
the default DNS servers set to 1.1.1.1 and 1.0.0.1.

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Re: End-user troubleshooting of bad c-ares interaction with router

2024-01-17 Thread Brad House via c-ares


What version of c-ares is installed?

What DNS servers are configured on your MacOS system when its not 
operating properly?  The output of "scutil --dns" would be helpful here.


On 1/17/24 12:09 PM, Nicholas Chammas via c-ares wrote:

Hello,

I am trying to troubleshoot a problem as an end-user of c-ares. I use 
a library (Apache Spark Connect 
) 
that uses gRPC, which in turn uses c-ares. I am two levels removed 
from c-ares itself and am a little out of my depth.


I have a little Python script that connects to a remote Apache Spark 
cluster via Spark Connect and runs a test query. When I run this 
script on my home network, it takes over 20 seconds to run. When I 
tether my workstation to my phone (which is connected via LTE), the 
same script runs in a second or two. In both cases the script runs 
successfully.


I enabled some gRPC debug flags which print out a lot of information. 
This led me to c-ares, as I believe the difference in runtime is 
related somehow to DNS.


I’ve extracted the log lines output by gRPC related to c-ares 
. 
(Be sure to scroll down to see both files; there is one for home and 
one for LTE.) The gRPC codebase is hosted on GitHub, where you can 
find the grpc_ares_wrapper.cc 
 file 
mentioned in the log files.


I tried changing the DNS servers configured in my home router but that 
didn’t seem to help. Interestingly, however, if I set the same DNS 
servers already configured in my home router directly on the network 
interface I’m using, the 20 second delay disappears:


```
networksetup -setdnsservers “My Network" 1.1.1.1 1.0.0.1
```

But this setting doesn’t persist across restarts, and only Spark 
Connect seems to have this problem. It seems there is some kind of bad 
interaction between c-ares and my router.


How can I dig deeper to understand what’s going wrong with my home 
network? I checked the c-ares docs  but 
I don’t see a way for an end-user to enable debug output from c-ares, 
e.g. via an environment variable.


Any suggestions? I’m running macOS 14.2.1. The router is an Apple AirPort.

Nick

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End-user troubleshooting of bad c-ares interaction with router

2024-01-17 Thread Nicholas Chammas via c-ares

Hello,

I am trying to troubleshoot a problem as an end-user of c-ares. I use a library 
(Apache Spark Connect 
) that uses 
gRPC, which in turn uses c-ares. I am two levels removed from c-ares itself and 
am a little out of my depth.

I have a little Python script that connects to a remote Apache Spark cluster 
via Spark Connect and runs a test query. When I run this script on my home 
network, it takes over 20 seconds to run. When I tether my workstation to my 
phone (which is connected via LTE), the same script runs in a second or two. In 
both cases the script runs successfully.

I enabled some gRPC debug flags which print out a lot of information. This led 
me to c-ares, as I believe the difference in runtime is related somehow to DNS.

I’ve extracted the log lines output by gRPC related to c-ares 
. (Be sure 
to scroll down to see both files; there is one for home and one for LTE.) The 
gRPC codebase is hosted on GitHub, where you can find the grpc_ares_wrapper.cc 

 file mentioned in the log files.

I tried changing the DNS servers configured in my home router but that didn’t 
seem to help. Interestingly, however, if I set the same DNS servers already 
configured in my home router directly on the network interface I’m using, the 
20 second delay disappears:

```
networksetup -setdnsservers “My Network" 1.1.1.1 1.0.0.1
```

But this setting doesn’t persist across restarts, and only Spark Connect seems 
to have this problem. It seems there is some kind of bad interaction between 
c-ares and my router.

How can I dig deeper to understand what’s going wrong with my home network? I 
checked the c-ares docs  but I don’t see a way 
for an end-user to enable debug output from c-ares, e.g. via an environment 
variable.

Any suggestions? I’m running macOS 14.2.1. The router is an Apple AirPort.

Nick

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c-ares mailing list
c-ares@lists.haxx.se
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End-user troubleshooting of bad c-ares interaction with router

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