Distance Vector (DV) protocols like RIP and IGRP operate by having each router maintain a table containing the distances (costs) to all possible destinations. These tables are periodically shared with directly connected neighbors. In contrast, Link State (LS) protocols such as OSPF and IS-IS require each router to maintain:

// Pseudocode for LS database structure
struct LSDB {
    RouterID originator;
    List<Link> connectedLinks; 
    SequenceNumber seq;
    TimeStamp age;
}

The critical distinction lies in how they handle network changes. DV protocols suffer from the "count to infinity" problem during convergence:

# Example of count-to-infinity scenario
RouterA -> RouterB (cost 1) 
RouterB -> RouterC (cost 1)
When A-C link fails:
RouterB advertises C as distance 2
RouterA advertises back as 3
This ping-pong continues until infinity (16 in RIP)

LS protocols flood LSPs (Link State Packets) across the network, allowing all routers to build identical topological maps using Dijkstra's algorithm:

// Dijkstra implementation snippet
void computeShortestPath(Graph g, Node source) {
    PriorityQueue pq;
    for (Node v : g.vertices) {
        dist[v] = INFINITY;
        pq.insert(v, dist[v]);
    }
    dist[source] = 0;
    while (!pq.empty()) {
        Node u = pq.extractMin();
        for (Edge e : u.edges) {
            if (dist[e.v] > dist[u] + e.weight) {
                dist[e.v] = dist[u] + e.weight;
                pq.decreaseKey(e.v, dist[e.v]);
            }
        }
    }
}

Resource Requirements: LS protocols demand more memory (to store the entire topology) and CPU (for SPF calculations). DV protocols require less overhead but may converge slower.

Implementation Example - OSPF vs RIP:

// Cisco config comparison
# RIP implementation
router rip
 network 192.168.1.0
 version 2

# OSPF implementation 
router ospf 1
 network 10.0.0.0 0.255.255.255 area 0
 passive-interface default
 no passive-interface Ethernet0/0

EIGRP combines aspects of both approaches as an advanced distance vector protocol, using DUAL (Diffusing Update Algorithm) for faster convergence. Modern SDN architectures often leverage LS principles for centralized path computation.

When choosing between approaches, consider:

• Network size (LS scales better for large networks)
• Convergence speed requirements
• Hardware capabilities of routers
• Administrative domain boundaries

Distance Vector protocols (like RIP) and Link State protocols (like OSPF) represent fundamentally different approaches to route calculation. Distance Vector protocols operate on the Bellman-Ford algorithm where routers only know about their directly connected neighbors and the "distance" (metric) to destinations. In contrast, Link State protocols use Dijkstra's algorithm where each router maintains a complete topological map of the network.

// Simplified Distance Vector pseudocode
function distanceVectorUpdate():
    for each neighbor:
        send routing table (destinations + metrics)
    receive updates from neighbors
    recalculate best paths based on received metrics + link costs

// Simplified Link State pseudocode  
function linkStateOperation():
    flood LSA (Link State Advertisements) to entire network
    build complete topology database
    run SPF (Shortest Path First) calculation
    populate routing table with shortest paths

Link State protocols typically converge faster after topology changes because all routers have full topology information. Distance Vector protocols suffer from slower convergence due to the "counting to infinity" problem and periodic update mechanisms. However, Link State protocols consume more memory to store the complete topology database.

• CPU Usage: Link State requires more CPU for SPF calculations, especially in large networks
• Memory Usage: Link State maintains full topology database (O(n) space complexity)
• Bandwidth: Distance Vector uses periodic full updates, Link State uses triggered incremental updates

Here's basic configuration for both protocols in Cisco IOS:

! RIP (Distance Vector) Configuration
router rip
 version 2
 network 192.168.1.0
 no auto-summary

! OSPF (Link State) Configuration  
router ospf 1
 network 10.0.0.0 0.255.255.255 area 0
 passive-interface default
 no passive-interface GigabitEthernet0/1

Modern protocols like EIGRP combine aspects of both approaches. EIGRP maintains neighbor topology tables like Link State but exchanges routing information like Distance Vector, offering faster convergence than traditional Distance Vector while being less resource-intensive than pure Link State.

Link State protocols generally offer better security as they authenticate each LSA packet. Distance Vector protocols are more vulnerable to route poisoning attacks. Always implement authentication for production networks:

! OSPF Authentication Example
interface GigabitEthernet0/1
 ip ospf authentication message-digest
 ip ospf message-digest-key 1 md5 OurSecureKey123