I’m really ashamed. In my state of exhaustion, I never looked at the photos and when the parcel arrived this afternoon, I said to my wife, “what a huge box for something the size of a fish finger", and Janet said, “well there is a power supply with it". I said "what?" and opened up the box. All this time I had been thinking that I was ordering a ‘dongle’ - a 4G USB NIC.
That explains the strange comments that I made earlier, such as "It should just work". As far as the Firebrick goes, I have a similar interfacing problem as with the SXT, how to make a PPPoE modem do failover. But doing PPPoE modems is easy, I have those already. I just need to work out how to do failover, but I think I know how to do that, using ‘profiles’. These are Firebrick predicates plus conditional-if attributes that you apply to elements/objects. I already use these for various things. They say ‘if this test/predicate expression is true, then the profile value is true" and where they are applied they mean something like "do this/make this apply/make this object exist if the profile is true". With USB dongles, the Firebrick has built in failover awareness, so the failover rules are predefined so you don’t have to do anything or understand profiles.
I may have a problem with MTU though. Can this device handle PPP MTU 1508 bytes for PPP+PPPoE ? My 3G USB NIC currently fragments IPv4 packets because the IP MTU size remains at 1500 bytes, and the stupid IP MTU is something like 1440 (iirc). I’ve set the IPv6 IP MTU to 1408 bytes permanently, regardless of failover mode, ie IP 1408 bytes even in normal non-failover mode. This is because the carrier doesn’t support IPv6 so I have to have the additional overhead of a 20 byte IPv4 header for AA’s 6in4 tunnel, proto-41 static (ie. IPv6 in IPv4 straight tunnelling). That will remain the case and I will still have to have a reduced MTU for IPv6 unless the service can cope with a PPP MTU of 1528 bytes in larger baby jumbo PPP PDUs.
