Routing protocols help routers automatically learn and update routes.
The three most important routing protocols are:
- RIP
- OSPF
- BGP
These represent distance-vector, link-state, and path-vector protocols.
🌟 1. RIP (Routing Information Protocol)
✔ Type: Distance-vector routing protocol
RIP selects routes based on hop count.
✔ Key Characteristics
- Metric Used: Hop Count
- Maximum hop count = 15
- 16 = Unreachable
- Algorithm: Bellman–Ford
- Updates: Sent every 30 seconds
→ slow convergence - Port: UDP 520
- Versions:
- RIP v1: Classful (does not support subnet masks)
- RIP v2: Classless (supports CIDR, subnetting, multicast updates)
✔ Where RIP is used?
- Very small networks
- Simple topologies
- Low-cost implementations
✔ Advantages
- Very easy to configure
- Low overhead
- Lightweight protocol
✔ Limitations
- Not scalable
- Slow convergence
- Hop count limitation
- Inefficient for medium/large networks
✔ Remember
RIP = simple + small networks only
🌟 2. OSPF (Open Shortest Path First)
✔ Type: Link-state routing protocol
OSPF builds a complete map of the network and calculates the shortest path.
✔ Key Characteristics
- Metric Used: Cost (based on bandwidth)
Higher bandwidth = lower cost - Algorithm: Dijkstra’s SPF (Shortest Path First)
- Updates: Only when a change occurs
→ very fast convergence - Port: IP Protocol 89
- Classless: Supports VLSM, CIDR, and subnetting
- Security: Supports authentication
✔ Hierarchical Design
OSPF organizes networks into areas for efficiency.
- Area 0 (Backbone Area): Core of OSPF
- Additional areas connect to Area 0
✔ Key OSPF Terms
- LSA (Link-State Advertisement):
Messages that share network information - DR/BDR (Designated Router / Backup DR):
Reduces update overload in multi-access networks (e.g., LAN)
✔ Advantages
- Very fast convergence
- Highly scalable
- Efficient routing
- Supports large enterprise networks
✔ Limitations
- More complex to configure
- Requires more CPU and memory than RIP
✔ Remember
OSPF = Fast + Efficient + Enterprise Networks
🌟 3. BGP (Border Gateway Protocol)
✔ Type: Path-vector routing protocol
Used for routing between Autonomous Systems (AS) across the Internet.
✔ Key Characteristics
- Used by: ISPs, large organizations, backbone routers
- Metric: Path attributes
(AS-PATH, NEXT-HOP, LOCAL-PREF, etc.) - Algorithm: Policy-based routing
→ Decisions are based on routing policies, not shortest path - Updates: Only when changes occur
→ very stable - Port: TCP 179
✔ Key Terms
- AS (Autonomous System):
A group of routers under one organization (e.g., ISP) - eBGP (External BGP):
Routing between different AS - iBGP (Internal BGP):
Routing within the same AS
✔ Advantages
- Extremely scalable
- Can handle the entire Internet routing table
- Supports policy-based routing (flexible and powerful)
✔ Limitations
- Complex to configure
- Needs powerful routers
- Slow convergence compared to OSPF
✔ Remember
BGP = Internet’s main routing protocol (very large networks)
🌟 4. Quick Comparison
| Feature | RIP | OSPF | BGP |
|---|---|---|---|
| Type | Distance-vector | Link-state | Path-vector |
| Best For | Small networks | Enterprise networks | Internet-scale routing |
| Metric | Hop Count | Cost (bandwidth) | Path attributes |
| Algorithm | Bellman-Ford | Dijkstra (SPF) | Policy-based |
| Updates | Every 30 sec | Only on changes | Only on changes |
| Convergence | Slow | Fast | Slow-to-medium |
| Port | UDP 520 | IP protocol 89 | TCP 179 |
| Scalability | Low | High | Very High |
| Version | RIP v1/v2 | OSPFv2/v3 | BGP-4 |
🌟 5. Quick Mnemonics
✔ RIP
“15 hops is all you RIP!”
Limited to 15 hops → small networks.
✔ OSPF
“Open to all areas, cost matters!”
Multi-area + cost-based metric.
✔ BGP
“Biggest Global Protocol!”
Used on the Internet between ISPs.
🌟 6. Exam Focus Points
- RIP uses hop count, max 15
- OSPF uses cost (based on bandwidth)
- BGP uses path attributes
- RIP uses UDP 520
- OSPF uses IP Protocol 89
- BGP uses TCP 179
- OSPF divides networks into areas (Area 0 = backbone)
- BGP is used for inter-AS routing
- RIP is slow, OSPF is fast, BGP is very scalable
These points regularly appear in IBPS IT Officer, SBI SO, RBI Grade B DSIM/DEPR Tech, internal promotions and other exams.
🌟 7. Final Summary
- RIP → Simple, small networks, hop count metric, slow updates
- OSPF → Fast, scalable, Dijkstra’s algorithm, enterprise networks
- BGP → Highly scalable, Internet routing, policy-based, TCP 179
Each protocol has different strengths depending on the size and requirement of the network.