Network Routing and Switching Fundamentals

Network Routing and Switching

Switching: The process of moving packets from a router's input to the appropriate router output.

Routing: The process of determining the specific route taken by packets across a network.

Ethernet Frames and IP Datagrams

Ethernet frames: These typically have a Maximum Transmission Unit (MTU) of 1500 bytes.

IP Datagram: Key components include the identification flag (where the last fragment has the bit set to zero) and travel/offset (which specifies the exact location of the fragment).

Address Resolution Protocol (ARP)

ARP: IP ARP is used to determine the physical address (MAC) of the next hop. It sends ARP requests for the destination MAC in broadcast mode, receives the response in unicast mode, and then forwards the packet in unicast mode.

MAC Address: A 48-bit address represented in hexadecimal format.

ICMP and IPv6 Standards

ICMP: Operating at the network layer, ICMP serves to control errors and warnings. ICMP messages always report errors back to the host of origin, such as destination unreachable, traffic congestion, or time exceeded.

IPv6: A 128-bit addressing system with a fixed header of 40 bytes, featuring labeling and flow priority.

IPv6 over IPv4 Transition

• Dual Stack: Used only if all nodes and means work on IPv6.
• Tunneling: Used when routers in the path do not support IPv6.

Routing Types and Metrics

Static Routing: Administrative routes manually created by the network administrator; if a link fails, these routes must be manually redone.

Dynamic Routing: Routing tables are built automatically by routing protocols.

Metric: The cost of passage. Routers are programmed to choose the path with the lowest metrics.

Routing Protocols: Common examples include RIP, OSPF, and BGP.

Distance Vector and Link State Protocols

Distance Vector: Each router shares its knowledge of connected networks with its neighbors through protocols. The algorithm knows its own interfaces and shares information only with immediate neighbors at regular time intervals.

Link State (OSPF): All routers maintain the same database of link states.

• Area: A collection of networks, hosts, and routers connected to an administrative system.
• Border Router: A router located at the Autonomous System (AS) border.

Each router shares knowledge about its neighborhood with other routers in the area; eventually, every router receives a copy of the same information. Sharing occurs immediately when a router detects a change.

General Idea: Each router maintains an accurate and complete description of the network topology.

Border Gateway Protocol (BGP)

BGP (Path Vector): Table entries include the destination network, the next hop, and the specific path to reach the destination.

Loops: To prevent loops, each router checks if its own identifier is already on the path to the destination. Each router applies specific policies from the origin to the destination.