Inter-Domain vs Intra-Domain Routing: Identifying the Correct Protocol (RIP, OSPF, BGP)
Inter-domain routing refers to routing between different administrative routing domains, most commonly modeled as Autonomous Systems (ASes). In practice, routing between ASes is performed by BGP. By contrast, RIP and OSPF are interior gateway protocols (IGPs) used within a single AS.
A useful mental model is:
- Inside an AS: use an IGP (e.g., RIP, OSPF)
- Between ASes: use an EGP (e.g., BGP)
The correct option for “Which of the following is an inter-domain routing protocol?” is: (iii) BGP.
BGP vs OSPF (Inter-domain vs Intra-domain) Overview
How to Identify an Inter-Domain Routing Protocol
- 1Step 1
Ask whether the protocol runs inside one Autonomous System or between Autonomous Systems.
- 2Step 2
IGPs are used intra-domain; EGPs are used inter-domain.
- 3Step 3
RIP and OSPF are IGPs (intra-domain), while BGP is the EGP (inter-domain).
- 4Step 4
From (i) RIP, (ii) OSPF, (iii) BGP, choose (iii) BGP.
Pro Tip
If a question mentions “between Autonomous Systems” or “edge connectivity across networks,” the answer is usually BGP (inter-domain).
Common Exam Trap
Don’t confuse route computation with route exchange scope: RIP and OSPF may exchange routes, but they are intended for intra-AS operation, not inter-AS routing.
Protocol Scope: Intra-Domain (IGP) vs Inter-Domain (EGP)
High-level mapping used for exam classification.
Routing Protocol Roles Across Domains
Within one AS
Step 1Use an IGP to learn routes inside the domain (e.g., RIP, OSPF)."
At AS boundaries
Step 2Use BGP to exchange reachability with other ASes."
End-to-end reachability
Step 3IGPs provide internal forwarding; BGP provides inter-AS path selection."
Quick Concept Check
Inter-Domain Routing Flashcards
Knowledge Check
Which of the following is an inter-domain routing protocol?