On 2019-12-09 13:48,
kitepilot@kitepilot.com wrote:
> Matt Graham writes:
>> I think I turned on both wired and wireless networking
>> on my laptop at some point, and it didn't break
>> everything. [...] This is *not* recommended, but it
>> should not be the horrible failure you got in the
>> 2000s if you had 2 wired Ethernet devices on the same
>> machine in the same subnet.
> Finally, this explanation is watered down to dilution because I don't
> have a lot of time right now.
TL;DR: AFAICT, what you said would happen either does not happen or is
not nearly as problematic as you said it was.
> There is no guarantee (that I know of) that the kernel will search
> the network interfaces in any particular order for a matching subnet,
> and the search will stop as the first one is found.
>
> That creates a race condition with the ARP table where a packed may
> be sent while the ARP table gets refreshed and moved to the other
> interface, and those packets will die a slow death. That will create
> random connection drops and transmission slowdowns.
I took my laptop and did "dhcpcd -d wlp3s0" on it since it was already
plugged in to a wired network. This resulted in its enp1s0 having
192.168.2.26/24 and its wlp3s0 having 192.168.2.23/24 . (The IPv6 addrs
were different, but that's probably not a factor.) Subsequent going to
web pages, pinging things, scp'ing large files, and other network
operations on the laptop showed zero performance degradation. Or maybe
I just got lucky? It's difficult to tell with a very limited time test,
but usually networking trouble gives you stalls and failures instead of
fast scp'ing and web pages showing up quickly.
Please note that doing this with 2 wired interfaces in the 2000s caused
all network operations to barf ingloriously until the subnets got fixed.
This laptop and desktop are running pretty recent kernels though. The
kernel and/or networking people may have put some code in somewhere that
says "Have the users done something idiotic like have 2 NICs in the same
subnet? Try not to barf," because people can be pretty dumb.
--
Crow202 Blog:
http://crow202.org/wordpress
There is no Darkness in Eternity
But only Light too dim for us to see.
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