19: IP and Routing Tables

IPv4 Version Field

A field in the IP header that indicates the version of the IP protocol being used, in this case, version 4.

IHL (Internet Header Length)

A field that specifies the length of the IP header in 32-bit words.

DSCP (Differentiated Services Code Point)

A field used for Quality of Service (QoS) to prioritize different types of network traffic.

TTL (Time to Live)

A mechanism that limits a packet's lifetime to prevent infinite loops; each router decrements this value.

Fragmentation

The process of breaking IP packets into smaller pieces to fit within the Maximum Transmission Unit (MTU) of a link.

Identification Field

A unique value used to identify all fragments of a single original IP packet so they can be reassembled.

Fragmentation Offset

Indicates the exact position of a specific fragment relative to the start of the original data payload.

"Don’t Fragment" (DF) Flag

A bit in the Flags field; if set to 1, the packet cannot be fragmented even if it exceeds the MTU.

Path MTU Discovery

A technique using ICMP messages to find the largest MTU supported across a destination path without fragmentation.

Routing Table

A database stored in a router or network host that lists the paths to particular network destinations.

Hierarchical Addressing

An addressing scheme where multiple devices share a common network prefix to minimize routing table entries.

Default Route

A catch-all routing entry used when no specific match for a destination address is found in the routing table.

Source Independence

A property of routing tables where the next hop is determined solely by the destination address, regardless of the source.

Static Routing

Manual entry of routes into a routing table by an administrator; it is inflexible to network changes.

Dynamic Routing

A method where routers use protocols to communicate and automatically update tables based on current network topology.

Dijkstra’s Algorithm

A graph-based algorithm used to find the shortest path between a source node and all other nodes in a network.

Benefits of Static Routing

Minimal CPU and bandwidth usage, increased security, and precision in path selection for small networks.

Limitations of Static Routing

Difficult to scale and requires manual configuration updates for every change in network topology.

Benefits of Dynamic Routing

High scalability and the ability to automatically recover and reroute traffic during network link failures.

Limitations of Dynamic Routing

Consumes more router resources (CPU, memory, and bandwidth) and is more complex to troubleshoot.

Benefits of Hierarchical Addressing

Supports route summarization, which reduces the number of entries in routing tables and improves processing speed.

Limitations of IPv4

Face severe exhaustion of the 32-bit address space and lacks mandatory, built-in security features like encryption.

Disadvantages of Fragmentation

Increases destination host CPU usage for reassembly and introduces latency or packet loss if fragments are dropped.