Consumer networking head scratcher

Thu Mar 2 17:00:30 UTC 2017

On Thu, Mar 2, 2017, at 12:24 AM, Roland Dobbins wrote:
> On 2 Mar 2017, at 9:55, Oliver O'Boyle wrote:
> 
> > Currently, I have 3 devices connected. :)
> 
> You could have one or more botted machines launching outbound DDoS 
> attacks, potentially filling up the NAT translation table and/or getting 
> squelched by your broadband access provider with layer-4 granularity.  
> And the boxes themselves could be churning away due to being compromised 
> (look at CPU and memory stats over time).  Aggressive horizontal 
> scanning is often a hallmark of botted machines, and it can interrupt 
> normal network access on the botted hosts themselves.
> 
> I don't actually think that's the case, given the symptomology you 
> report, but just wanted to put it out there for the list archive.
> 
> What about DNS issues?  Are you sure that you really have a networking 
> issue, or are you having intermittent DNS resolution problems caused by 
> flaky/overloaded/attacked recursivs, EDNS0 problems (i.e., filtering on 
> DNS responses > 512 bytes), or TCP/53 blockage?  Different host 
> OSes/browsers/apps exhibit differing re-query characteristics.  Are the 
> Windows boxes and the other boxes set to use the same recursors?  Can 
> you resolve DNS requests during the outages?
> 
> Are your boxes statically-addressed, or are they using DHCP?  
> Periodically-duplicate IPs can cause intermittent symptoms, too.  If 
> you're using the consumer router as a DHCP server, DHCP-lease nonsense 
> could be a contributing factor.
> 
> Are the Windows boxes running some common application/service which 
> updates and/or churns periodically?  Are they members of a Windows 
> workgroup?  All kinds of strange name-resolution stuff goes on with 
> Windows-specific networking.
> 
> Also, be sure to use -n with traceroute.  tcptraceroute is useful, too.  
> netstat -rn should work on Windows boxes, IIRC.
> 
> -----------------------------------
> Roland Dobbins <rdobbins at arbor.net>

It isn't a DNS issue as trying to access resources via IP address
directly also have the issue.

What became clear to me last night is that this actually also impacts my
Mac, and that it has to do with traffic not properly making it back to
my machines.  When the issue occurs, my traffic makes it out to the
destination, the destination responds, but that packet never makes it to
my laptop, for example.  I tested by sending traffic to a server I
control and doing PCAPs on both ends.

Thanks,
Ryan