Evening,
I've recently bought an RB3011 to upgrade from my RB450G, and am having issues with getting dual WAN to work reliably. It'll work for about 30 seconds, then all browsing dies (while working, pings to Google DNS are hit and miss, but when it all stops they stop too).
I copied the config from the RB450G directly onto the RB3011 (from fresh reset), and immediately one of the connections routes goes unreachable (ping-wise). Even though it says unreachable, I'm still able to browse albeit that stops soon after.
I posted something similar a while ago (https://forums.whirlpool.net.au/forum-replies.cfm?t=2540807) and have tried going through that again to make sure I didn't potato the config, but it's not working for me 
Current rules:
ip address print detail
Flags: X - disabled, I - invalid, D - dynamic
0 address=192.168.88.1/24 network=192.168.88.0 interface=LAN actual-interface=LAN
1 D address=119.xxx.xxx.xxx/24 network=119.xxx.xxx.xxx interface=IPoE actual-interface=IPoE
2 D address=118.xxx.xxx.xxx/32 network=203.xxx.xxx.xxx interface=pppoe-out1 actual-interface=pppoe-out1
ip route print detail
Flags: X - disabled, A - active, D - dynamic, C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme, B - blackhole, U - unreachable, P - prohibit
0 A S dst-address=0.0.0.0/0 gateway=203.xxx.xxx.xxx gateway-status=203.xxx.xxx.xxx reachable via pppoe-out1 check-gateway=ping distance=1 scope=30 target-scope=10 routing-mark=to_pppoe-out1
1 A S dst-address=0.0.0.0/0 gateway=119.xxx.xxx.xxx gateway-status=119.xxx.xxx.xxx reachable via IPoE check-gateway=ping distance=1 scope=30 target-scope=10 routing-mark=to_IPoE
2 A S dst-address=0.0.0.0/0 gateway=203.xxx.xxx.xxx gateway-status=203.xxx.xxx.xxx reachable via pppoe-out1 check-gateway=ping distance=4 scope=30 target-scope=10
3 DS dst-address=0.0.0.0/0 gateway=203.xxx.xxx.xxx gateway-status=203.xxx.xxx.xxx reachable via pppoe-out1 distance=4 scope=30 target-scope=10
4 DS dst-address=0.0.0.0/0 gateway=119.xxx.xxx.xxx gateway-status=119.xxx.xxx.xxx reachable via IPoE distance=5 scope=30 target-scope=10 vrf-interface=IPoE
5 S dst-address=0.0.0.0/0 gateway=119.xxx.xxx.xxx gateway-status=119.xxx.xxx.xxx reachable via IPoE check-gateway=ping distance=5 scope=30 target-scope=10
6 ADC dst-address=119.xxx.xxx.xxx/24 pref-src=119.xxx.xxx.xxx gateway=IPoE gateway-status=IPoE reachable distance=0 scope=10
7 ADC dst-address=192.168.88.0/24 pref-src=192.168.88.1 gateway=LAN gateway-status=LAN reachable distance=0 scope=10
8 ADC dst-address=203.xxx.xxx.xxx/32 pref-src=118.xxx.xxx.xxx gateway=pppoe-out1 gateway-status=pppoe-out1 reachable distance=0 scope=10
interface print detail
Flags: D - dynamic, X - disabled, R - running, S - slave
0 R name="IPoE" default-name="ether1" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:B3 fast-path=yes last-link-up-time=nov/23/2016 22:07:43 link-downs=0
1 R name="PPPoE" default-name="ether3" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:B5 fast-path=yes last-link-up-time=nov/23/2016 22:07:43 link-downs=0
2 XS name="ether2" default-name="ether2" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:B4 fast-path=yes last-link-down-time=nov/23/2016 22:08:05 last-link-up-time=nov/23/2016 22:07:44
link-downs=1
3 XS name="ether4" default-name="ether4" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:B6 fast-path=yes link-downs=0
4 XS name="ether5" default-name="ether5" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:B7 fast-path=yes link-downs=0
5 RS name="LAN_ether6" default-name="ether6" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:B9 fast-path=yes last-link-up-time=nov/23/2016 22:07:43 link-downs=0
6 XS name="ether7" default-name="ether7" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:BA fast-path=yes link-downs=0
7 XS name="ether8" default-name="ether8" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:BB fast-path=yes link-downs=0
8 XS name="ether9" default-name="ether9" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:BC fast-path=yes link-downs=0
9 RS name="LAN - WiFi" default-name="ether10" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1598 max-l2mtu=8156 mac-address=xx.xx.xx.xx.xx:BD fast-path=yes last-link-down-time=nov/23/2016 22:09:23 last-link-up-time=nov/23/2016 22:09:25
link-downs=3
10 XS name="sfp1" default-name="sfp1" type="ether" mtu=1500 actual-mtu=1500 l2mtu=1600 max-l2mtu=8158 mac-address=xx.xx.xx.xx.xx:B8 fast-path=yes link-downs=0
11 R name="LAN" type="bridge" mtu=auto actual-mtu=1500 l2mtu=1598 mac-address=xx.xx.xx.xx.xx:B4 fast-path=yes last-link-up-time=nov/23/2016 22:08:52 link-downs=0
12 X name="lte1" type="lte" mtu=1500 actual-mtu=1500 mac-address=xx.xx.xx.xx.xx.A2 fast-path=no last-link-down-time=nov/23/2016 22:08:52 last-link-up-time=nov/23/2016 22:07:59 link-downs=2
13 R name="pppoe-out1" type="pppoe-out" mtu=1480 actual-mtu=1480 fast-path=yes last-link-up-time=nov/23/2016 22:09:02 link-downs=0
ip firewall export
nov/23/2016 22:18:24 by RouterOS 6.35.4
software id = xxxx.xxxx
/ip firewall filter
add chain=input protocol=icmp
add chain=input connection-state=established,related
add action=drop chain=input in-interface=IPoE
add action=fasttrack-connection chain=forward connection-state=established,related
add chain=forward connection-state=established,related
add action=drop chain=forward connection-state=invalid
add action=drop chain=forward connection-nat-state=!dstnat connection-state=new in-interface=IPoE
/ip firewall mangle
add action=mark-connection chain=input in-interface=pppoe-out1 new-connection-mark=ISP1
add action=mark-connection chain=input in-interface=IPoE new-connection-mark=ISP2
add action=mark-routing chain=output connection-mark=ISP1 new-routing-mark=to_pppoe-out1
add action=mark-routing chain=output connection-mark=ISP2 new-routing-mark=to_IPoE
add chain=prerouting dst-address=192.168.88.0/24 in-interface=LAN
add action=mark-connection chain=prerouting dst-address-type=!local in-interface=LAN new-connection-mark=ISP1 per-connection-classifier=both-addresses-and-ports:2/0
add action=mark-connection chain=prerouting dst-address-type=!local in-interface=LAN new-connection-mark=ISP2 per-connection-classifier=both-addresses-and-ports:2/1
add action=mark-routing chain=prerouting connection-mark=ISP1 in-interface=LAN new-routing-mark=to_pppoe-out1
add action=mark-routing chain=prerouting connection-mark=ISP2 in-interface=LAN new-routing-mark=to_IPoE
/ip firewall nat
add action=masquerade chain=srcnat comment="" out-interface=IPoE
add action=masquerade chain=srcnat out-interface=pppoe-out1
As far as I can tell (and from the online guides for Dual WAN) it all looks correct, however is very hit and miss for me.
The other part I don't understand (though could be a misconception on my part) is why routes 3, 4 & 5 show as reachable but are not active? These same routes also go unreachable as well.
Any help would be greatly appreciated.