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- Routers have to have at least 2 networks, usually have 4 ethernet ports
- Metaphor of routing:
- Suppose I want my Aunt on the other side of the country to hear a song I have on my computer?
- Application Header + data = music
- TCP header = CD
- IP header = Box
- Frame Header + Frame Trailer = FedEx car
- If communicating outside of network, has to go through router, takes 2 layer 2 artifacts to go between Stevens and Perlman
- If same network, destation AP address's MAC address
- If different, the default Gateway's MAC address / router's MAC address
- PC1 wants to send something to PC2
- Layer 2 = MAC address
- Layer 3 = IP address
- MAC address changes with each router
- If not on router's network, send out ARP
- FA0/0 = ethernet; S0/0/0 = serial
- ARP spoofing
- pretend to be router to victim and victim to router
- don't necessarily do anything, can just read it
- Dynamic routing protocols
- are "distributed algorithms"
- there is no central authority
- each router follows local rules
- global behavior emerges from group
- Interior Gateway Protocols (IGP) and Exterior Gateway Protocols (EGP)
- Autonomous Systems
- Routing Information Protocol (RIP) was originally specified in RFL 1058
- Distance vector routing protocol using the Bellman-Ford Algorithm
- Hop count is used as the metric for path selection
- If the hop count is greater than 15, the packet is discarded
- Routing updates are broadcast every 30 seconds, by default
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