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millenium7
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Posts: 297
Joined: Wed Mar 16, 2016 6:12 am

LTE failover just doesn't work properly

Tue Apr 16, 2019 7:56 am

We've had a growing number of complaints about backup 4g/LTE services just not working and it's been a constant source of frustration for both parties, as whenever I tested is in the lab and heck even on site it would work just fine

Our primary internet service is delivered via PPPoE so if there's a break anywhere to the PPPoE concentrator their interface will go down, which is technically better than ethernet for failover because the whole interface drops thus all connections related to that interface should as well. However something just isn't working properly
Yes, when the PPP drops and the next best route is through LTE it does work... Sort of... Anything TCP based i.e. web sites will drop and reestablish a connection after a short period of time. However UDP and ICMP don't. If I run a continual ping then kill the PPPoE session, pings will continue to fail until I manually stop it on the PC and start the ping again.
I think (can't remember for certain) dropping all connections in IP firewall on the Mikrotik works as well?

Is there a proper, solid, reliable method for LTE failover with Mikrotik? We can't have "sometimes maybe good, sometimes maybe shit" failover solutions like this. It needs to 'just work'
I don't know if the problem is sticky connections on the PC side, in the Mikrotik connections, NAT with wrong IP or something else
 
cantanko
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Joined: Mon Apr 05, 2010 12:53 am

Re: LTE failover just doesn't work properly

Tue Apr 16, 2019 1:54 pm

I have seen a similar thing - whilst it doesn't impact me to the same extent as your scenario, it is still annoying. TL;DR - found it was related to conntrack (although not sure my understanding of the entire packet processing model is sufficient to say this is the root cause) - flushing the conntrack table by issuing
/ip firewall connection remove [find]
when the primary connection goes away may fix it for you. This is a somewhat brute-force method and you'd need a way of triggering a script when the default gateway changes, but it may help :-)
 
gotsprings
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Posts: 911
Joined: Mon May 14, 2012 9:30 pm

Re: LTE failover just doesn't work properly

Fri Apr 19, 2019 3:08 pm

I use recursive routing and ping one if the DNS servers with netwatch. When it goes down... I use the connections flush method. Works perfectly.
"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."
Mark Twain

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