- Because not one organization owns all the networks, the routing is done in a hierarchical way.
- Intra-AS: When routing is done within the same network. ex) Using desktop connected with campus network to use LumiNUS.
- Inter-AS: When packet goes through multiple networks before it reaches the destination.
- In CS2105, every link has a cost. The problem is to find the path with the least amount of cost (Bellman-Ford algorithm)
Routing Algorithms
- "link state" algorithm
- Every router broadcasts the costs of the links that it is connected to.
- Every router has clear view of the network topology and link cost.
- Then we use Dijkstra's algorithm to compute the least cost path.
- "Distance vector" algorithm
- Routers exchange the "local views" (link costs) with its direct neighbors.
- The global view of the costs get iteratively better.
- C (x, y) is fact.
- D_x(y) is computed.
Bellman-Ford Equation:
- RIP is insensitive to network congestion:
- In the diagram drawn above, there is one 4-hop path and 2-hop path.
- Even if 2-hop path is more congested than the 4-hop path, the router will still choose 2-hop path.
- UDP is used because TCP will have to make 3-way handshake everytime an information is being sent, which takes up too much time.
- NAT sits at the boundary between public and private IP.
- It helps translates the private IP address to a public one.
- This is necessary because for example, NTU and NUS computers can have the same private IP address. If it tries to send a packet to facebook, the facebook does not know where to send the reply packet to.
- The NAT router must remember the port number of the source as well.
- The diagram shows why port numbers must be remembered.
- The two computers A and B may have the same public IP address after going through NAT router.
- The only difference the router can tell when it receives reply packets is the port number.
- LAN: Local Area Network
- WAN: Wide Area Network.
- ipconfig /all to view all my private addresses.
everything happens for a reason