Depending on the hardware you're talking about you should take different considerations.
For instance Cisco provides a dedicated set of port/RAM and flash for OOB access on SUP2T, so you would be able to access to your device even when RP hangs. OTOH, in some Juniper boxes, the management port is attached directly to the RE and so you should easily hang your router from there.
That said, I would recommend you to put a management CPE between your devices and your OOB internet access and set up a GRE tunnel between it and your central management server.
First off - your English appears to me to be excellent. Secondly your summation of bridging (question 1) and consequently your understanding of the subject are very good. I would probably word some of that slightly different but your summation is fair and it appears that your understanding is good.
Let's make one assumption at this point to keep things simple - this is all Ethernet and IP.
Having said that there are two steps that I would add to your bridging summation that might clear up your understanding of routing (question 2) a little:
- when your network stack is handed data to transmit there is a route table look up done (every device on an IP network contains a route table - to see it from a command prompt - on linux type "route", on windows type "route print".) to determine two things:
a) which interface to transmit the data out
b) if the destination is directly reachable or is remote (beyond a router).
- Once the route is determined the network stack will ARP for a MAC address.
So when Alice is sending data to Charlie she does a route lookup - it is determined that his machine is directly accessible on the LAN. She then ARPs for his MAC address. Once the route has been determined and the MAC address has been acquired the network stack can then assemble the packet for transmission. This particular conversation as you mentioned only traverses switch A as it inspects the destination MAC.
Now that we have fleshed out question one a little better let's apply some of these concepts to question 2.
When Alice desires to send data to Bob the first step is a route lookup. It is determined that Bob is not on the LAN. Thus the route to Bob is the default route (assuming Router A is configured as such). (As your book points out Router A - and by extension Alice - don't know where Bob is. They only know the general direction - or "route".) So Alice ARPs for Router A. Then assembles the packet with destination IP address(network layer) of Bob and MAC address(datalink layer) of Router A. Upon receiving this packet Router A 1)strips off the MAC address(datalink layer) of Alice 2)does a route lookup 3)ARPs for router B 4)then reassembles the packet with MAC address of Router B. Router B repeats these steps ARPing for Bob and forwards the packet.
So the network layer is assembled at the start - source Alice and destination Bob - and never changes. The datalink layer on the other hand is deleted and reassembled each and every leg of the trip.
Best Answer
You may have already learned that network addresses (routes) can be summarized. That is, many network addresses can be summarized (represented) by a single network address (i.e a route). A default route can be considered a summary route that contains all network addresses. Because routes can be summarized, routers may not have complete information about the entire internet, but they may have a route to a large summary network that contains the destination. That is, they know enough to forward the packet to another router that will have more information.
So if you send me data, your provider may not know where my IP address is located. But it may know that my IP is in the range of addresses that are located in the United States. So all your ISP needs to know is how to forward it to a router closer to the US. That router will have more information to get the packet closer to me. It in turn will forward to another router with more specific information, until the data gets to me.
The Tier 1 and Tier 2 providers that make up the backbone of the Internet have routers that carry routes to all the networks connected to the Internet (currently more than 500,000 routes). Your IP packet will eventually be forwarded to a router that does know to get to the destination network.