Hi,
I am considering a problem with my RB411. I have an extension card with SIM card and I am trying to make it work together. After enabling interface marked as ppp I have input an APN address taken from my ISP. Generally it authentificates and there are some new entries im my routing table. But if I try to ping whatever host in the Internet routing table gets clean and I have an error “no route to host” when pinging ;-( What I am doing wrong and why it happens???
Thanks in advance for help 
Do you have default gateway configured on your router?
Generally you should have the following entry,
/ip route add dst-address=0.0.0.0/0 gateway=x.x.x.x
You can set ‘add-default-gateway=yes’ in ppp-client configuration.
Default gateway is being added automatically. But it disappeares when I want to send a packet through teh router.
Make sure you do not have dial-on-demand enabled, set dial-on-demand=no and test again.
I have been trying with this checkbox enabled and disabled. When I disable and reenable all PPP client interface then I get 3 dynamic entries in routing table including default route to 0.0.0.0/0. PPP client status becomes “Waiting for packets”. After trying to ping any host on the Internet all dynamic entries in the routing table disappear and status changes to “Dialing”. Of course ping output is “no route to host” ;-( Any ideas?