Re: Altering preferred connection

[Colin Helliwell <colin helliwell ln-systems com>]

> On 07 July 2017 at 01:10 Greg Oliver <oliver greg gmail com> wrote:
.....
> I would really have completely different routing tables for this rather than changing metrics.  Source 
> routing /netfilter is your friend here, but source routing also comes with security risks, so you need to 
> make sure netfilter is stopping anything you do not want.  Basically, then you can easily say the interafce 
> it comes in on, it goes out of (or any interface you want...).

Thanks for the suggestion, Greg (and for your persistence in steering me towards other ways ;)).
I didn't relish delving into the topic, but it does look like I've been able to set up iptables rules to get 
the system a bit more flexible about the interface to use - certainly seems to be behaving more seamlessly, 
with less intervention required. (Mind you, I'm not sure if this is what you actually meant by 'different 
routing tables' - but perhaps it just demonstrates your point below!)

I still have slight niggle that what I've put in only works when my eth cable is unplugged - if it's an 
upstream failure then I guess the kernel simply can't know of that, and so it keeps trying on eth0 regardless.
I already have a script monitoring actual 'connectivity to the interweb', so I could use that to poke NM. I 
suspect, for that scenario, I probably ought to re-Up the eth0 connection anyway: dhclient ought to be re-run 
(and using autoconnect-retries=0) in case the outage was a reset of the broadband modem, which would warrant 
a renew/re-lease of the DHCP. (??)


> The good thing about the linux kernel is that there are usually ten(s) or more ways of doing what you 
> want/need.

Indeed...!