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| Question | Answer |
| What is forwarding and routing? | forwarding: refers to the router-local action of transferring the packet from an input link interface to the appropriate output link interface. Routing: refers to the network-wide process that determines end-to-end paths that packets take from source to destination. |
| What is a forwarding table? | Every router has one. A packet is examined by checking its header & using a value there to index into the table. The value in the table indicates the router's outgoing link interface |
| what does MTU stand for? | Maximum transition unit - the largest size packet or frame, specified in octets (eight-bit bytes), that can be sent in a packet- or frame-based network such as the Internet |
| What type of problem with MTU does fragmentation solve? | Each link have different MTU's, if one link has a smaller than the other, we might have problems sending a certain package. This is solved with IP fragmentation which involves breaking a datagram into a number of pieces that can be reassembled later (at the end system). |
| How does fragmentation work? | You use a flag and a an offset. The flag is 0 or 1, 0 indicating that that it is the last piece. 1 indicating that more pieces are coming. Offset shows where the piece should be inserted when the pieces are reasembled. It is given in byte. For ex: offset 370 means that you should insert the piece at bit 370*8 = 2960 |
| What does an "interface" refer to in addressing? | It is the boundary between host & physical link. Routers can have multiple interfaces, each for every link. OBS - in IPv4 each interface has its own IP-address |
| What is CIDR and what is it used for? | Classless InterDomain Routing (CIDR) was invented to keep the Internet from running out of IP Addresses. |
| How do we address in a subnetwork? | - Every subnet has a ”network address” - The remaining bits are used to address hosts - Every interface (including router!) has its own IP address - One address per subnetwork is used for broadcast (all 1’s in the host part) |
| If we write a IP address like this: 216.3.128.12/25 What does /25 stand for? | The number next to the slash (i.e. /25) represents the number of bits assigned to the network address. Which in this case leaves 32-25 bits to the address the host in the network |
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