I ordered and setup the following equipment for 2 businesses. The 2 owners are friends, and they have agreed to use each other's internet connections for failover in case the other's ISP fails.

Each location hasa miktrok RB751G router, a RB250GS switch, and a SXT 5HPnD radio (setup as a bridge between the offices).

Company A RB751G-2HnD - Has IP address of 192.168.10.1/24 on "bridge-local"
ether1 - 3.5G internet provider - IP address 192.168.30.5/24
ether2 - not used
ether3 - not used
ether4 - RB250GS switch
ether5 - SXT 5HPnD

Company B RB751G-2HnD - Has IP address of 192.168.20.1/24 on "bridge-local"
ether1 - DSL internet provider - Public IP address
ether2 - not used
ether3 - not used
ether4 - RB250GS switch
ether5 - SXT 5HPnD - IP address of 192.168.10.75

One issue that I can't get around is that Company A ISP's router does not support bridge mode, so, the ISP router's LAN ip is 192.168.30.1/24, and the mikrotik's ether1 has an ip of 192.168.30.5/24. I don't think this will make much of a difference, but, I figured it was worth noting.

I can get Company A's network to failover properly the way the setup is now, if the connection is lost with their ISP, and it begins to route everything over through Company B's router, and on to the internet.

What I'm having issues with, is getting Company B's network to failover to to Company A's network if their DSL connection fails.

I've tried the following, but ended up with some odd issues with company B's DHCP addresses on the WiFi side of things, making have to put the configuration back to the above.

I set up 2 vlans between the 2 mikrotiks, with vlan10 being the 192.168.10.0/24 and vlan30 being 192.168.30.0/24, and both vlans being added to the ethernet interfaces on the routers that have the SXT's connected.

On Company A's mikrotik, I created a bridge with an IP address of 192.168.30.5/24, and added ethernet1 and vlan30 to that bridge's ports.
I created another bridge with an IP address of 192.168.10.75/24, and added vlan10 to that bridge's port.
This should have left me with 2 possible default routes of 192.168.30.1, and 192.168.10.75.

On company B's mikrotik, I created a bridge with an IP address of 192.168.30.10/24, and added vlan30 as a port on that bridge.
I added vlan10 to the "default-bridge".
I removed ethernet1 from the "default-bridge", and left it alone to get an IP address from the DSL internet provider.
This should have left me with 2 possible default routes of 192.168.30.1, and the IP address of whatever ethernet 1 obtained from the DSL provider.

This in theory should work, and my problems could have been a typo on my part, but, it just seems to be a convoluted solution to what I'm trying to do.
Anyone have a suggestion for my attempt at vlans across the bridge, or a suggestion for a better solution?

BTW, if it helps, I can sketch up a diagram of the networks if need be.

ok so there is a few things, firstly its seems you are over complicating something to the max here, ive dont his before and vlans and all that is not required unless they are on the same ip range and so forth, so what you should do is on the one have a route that uses the 3g modem as a def gateway and has an metric of 1 with a check=ping for 0/0 and then you have an second route for 0/0 to the adsl with a metric of 2 on the other router you just have that in inverse, you can filter the routing and what not out and so if you dont want them to see each others pc's since they are on seperate ip ranges, you dont need vlans and all those intersting things since you have a flat routed network.

Have a look at this setup:
http://wiki.mikrotik.com/wiki/Advanced_ ... _Scripting

I admit, I always have a problem of trying to over complicate things...

So, trying to simplify things, and nixing the vlans...

On the ethernet ports on the routers for the wireless bridge between the two... Currently company A's router has an ip address in the subnet of Company B's network.
Can't I just create a small /30 subnet between the two routers? For instance, give the ethernet port 5 on company A an IP of 10.0.0.1/30, and give the ethernet port 5 on Company B an IP of 10.0.0.2/30?

Then, wouldn't it allow me to give each company 2 routes on each router; one being their own ISP, and the failover route being the 10.0.0.x of the other company's router?

If so, that would then let me use the routing failover setup without scripting as listed above?

Yes you can. Just keep in mind that the example on the wiki does not work when you specify
interfaces as gateway. It needs IP for gateways.
I have tested that example on an internet cafe of a customer of ours and it is working fine.