Static routes are fine for small networks, but larger networks use dynamic routing protocols so routers learn and adapt routes automatically. OSPF runs inside organisations; BGP runs the internet.
How OSPF Learns Routes
A link-state interior protocol: neighbours, LSAs and shortest-path first.
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Hello packets.
OSPF routers send Hello packets to find directly-connected neighbours in the same area and form adjacencies. OSPF is a link-state Interior Gateway Protocol (IGP).
Check your understanding
1. What type of routing protocol is OSPF?
2. What metric does OSPF use?
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The core idea
- OSPF is a link-state interior gateway protocol (IGP) using cost as its metric and areas for scale.
- BGP is a path-vector exterior protocol (EGP) that exchanges routes between autonomous systems — it runs the internet.
- Static routing is manual; dynamic routing adapts automatically when links change.
How BGP Runs the Internet
A path-vector exterior protocol exchanging routes between Autonomous Systems.
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eBGP / iBGP over TCP 179.
BGP routers form TCP peering sessions (port 179) between Autonomous Systems (eBGP) or within one (iBGP). BGP is the path-vector Exterior Gateway Protocol that runs the internet.
Check your understanding
1. What does BGP exchange routes between?
2. How does BGP prevent routing loops?
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How it works in practice
- OSPF is typical inside an enterprise; BGP is used by ISPs and for multi-homing.
- OSPF converges quickly within an area; BGP prioritises policy and stability.
- Autonomous System (AS) numbers identify networks in BGP.
Common mistakes
- Confusing interior (OSPF) with exterior (BGP) protocols.
- Expecting to run BGP inside a small LAN.
- Ignoring convergence behaviour when a link fails.
Why it matters for your career
OSPF and BGP are central to CCNA/CCNP and to any serious network engineering role — knowing where each fits is a strong signal.
Technical interview questions
- What is the difference between an IGP and an EGP?
- What metric does OSPF use?
- What protocol runs the internet's routing?
Practice questions
- Which protocol runs the internet? (BGP)
- What type of protocol is OSPF? (Link-state IGP)
- What identifies networks in BGP? (AS number)
Where this fits in your networking journey
This is one concept in the Networking Fundamentals path, which leads into CompTIA Network+ and Cisco CCNA. When this clicks, review Routing and continue with DNS & DHCP.
Practise with Missiora
- AI Interview™ — rehearse networking interview questions with scored feedback.
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