On the network shown in the figure, IS-IS runs on R1, R2, R4, and R5,...

Comprehensive and Detailed In-Depth Explanation:

Understanding the BGP and IS-IS Network Topology in the Question:

IS-IS Areas:

Area 49.0001 (Level-1 IS-IS): R1, R2, R4, R5.

Area 49.0002 (Level-2 IS-IS): R3, R6.

R2 acts as an ABR (Area Border Router) and redistributes routes between Level-1 and Level-2 using import-route isis level-2 into level-1.

BGP Route Reflection & Peering:

R2 and R5 are Route Reflectors (RRs).

iBGP peering is established among all routers (R1, R2, R3, R4, R5, R6).

R1 and R4 import 192.168.1.0/24 into BGP, meaning this prefix will be advertised to all iBGP peers.

R3 and R6 import 192.168.2.0/24 into BGP, meaning this prefix will also be advertised to all iBGP peers.

Route Distribution Analysis:

Route to 192.168.1.0/24 (Imported by R1 & R4):

R1 and R4 advertise 192.168.1.0/24 into iBGP.

Since R2 and R5 are Route Reflectors (RRs), they will reflect these routes to all their iBGP clients (R1, R3, R4, R6).

R2 learns two valid routes to 192.168.1.0/24 (from R1 and R4).

R5, as another RR, learns both routes and advertises them as well.

R2 ultimately has three valid paths (direct from R1 and R4, plus a reflected route from R5).✅ Statement C is correct: The BGP routing table of R2 contains three valid routes to 192.168.1.0/24.

R5 also learns 192.168.1.0/24 from both R1 and R4.✅ Statement B is correct: The BGP routing table of R5 contains two valid routes to 192.168.1.0/24 (from R1 and R4).

Route to 192.168.2.0/24 (Imported by R3 & R6):

R3 and R6 import 192.168.2.0/24 into BGP.

R2 and R5 (Route Reflectors) learn this route and reflect it to their clients (R1, R3, R4, R6).

R4 receives three valid paths (directly from R3 and R6 via BGP, and one additional reflected path via R5).✅ Statement D is correct: The BGP routing table of R4 contains three valid routes to 192.168.2.0/24.

Checking Statement A:

R3 originally imports 192.168.2.0/24 and advertises it.

Since it is a Route Reflector Client of R5 and R2, it should have multiple routes via iBGP, not just one.❌ Statement A is incorrect because R3 should have multiple valid routes, not just one.

Final Conclusion:

✅ B. The BGP routing table of R5 contains two valid routes to 192.168.1.0/24.✅ C. The BGP routing table of R2 contains three valid routes to 192.168.1.0/24.✅ D. The BGP routing table of R4 contains three valid routes to 192.168.2.0/24.❌ A. The BGP routing table of R3 does NOT contain only one valid route to 192.168.2.0/24 (it has multiple routes).

Thus, the correct answers are: B, C, D.