Comprehensive and Detailed In-Depth Explanation:
1. Understanding the Routing Issue
* R1 and R4 are BGP routers and have an IBGP connection.
* R2 and R3 are OSPF-only routers (they do not run BGP).
* Networks 10.1.1.0/24 and 10.4.4.0/24 are advertised into BGP but not OSPF.
* PC1 (10.1.1.1) and PC2 (10.4.4.1) need communication, but their networks are not known to OSPF routers R2 and R3.
To fix this, we need a method that ensures R2 and R3 learn the routes for 10.1.1.0/24 and 10.4.4.0/24.
2. Evaluating Each Answer Option
* Option A: "Deploy policy-based routing on R1 and specify R2 as the next hop for traffic from PC1 to PC2."
* Incorrect.
* Policy-Based Routing (PBR) does not solve the issue of missing routes in OSPF.
* Even if R1 forwards traffic to R2, R2 does not know how to reach 10.4.4.0/24, causing packet drops.
* A proper routing protocol solution is required instead of PBR.
* Option B: "Deploy MPLS and LDP on R1 to R4 and establish LSPs for routes 1.1.1.1/32 and
4.4.4.4/32."
* Incorrect.
* MPLS requires label-switched paths (LSPs) but does not distribute routing information itself.
* The real problem is that R2 and R3 do not have routing entries for 10.1.1.0/24 and 10.4.4.0/24.
* MPLS does not fix the missing route advertisement issue.
* Option C: "Run BGP on R2 and R3, and establish full-mesh IBGP connections in AS 123."
* Correct.
* If R2 and R3 run BGP, they can form IBGP sessions with R1 and R4 and learn routes 10.1.1.0
/24 and 10.4.4.0/24 via BGP.
* R2 and R3 would then be able to forward traffic correctly between PC1 and PC2.
* This is a valid method to fix the issue.
* Option D: "On R1 and R4, import routes 10.1.1.0/24 and 10.4.4.0/24 into OSPF."
* Correct.
* By redistributing BGP routes into OSPF, R1 and R4 can ensure that R2 and R3 learn the missing networks (10.1.1.0/24 and 10.4.4.0/24) via OSPF.
* This allows full reachability without running BGP on R2 and R3.
* This is another valid method to fix the issue.
Final Answer:
# C and D are correct.
HCIP-Datacom-Advanced Routing & Switching Technology References:
* BGP and OSPF Route Redistribution
* IBGP Full-Mesh Requirement and Route Propagation
* How Policy-Based Routing Works and Its Limitations