A confederated AS is comprised of three members. One member is comprised of 4 routers, while the other two members are comprised of 3 routers each. Assuming member ASs are fully meshed and use full mesh iBGP, what is the required number of BGP sessions within the confederation?

The total number of BGP sessions within a confederation is the sum of the internal BGP (iBGP) sessions within each member AS and the external BGP (eBGP) sessions between the member ASs.
1. iBGP sessions (within each member AS): The formula for a full mesh is n(n-1)/2. Member AS 1 (4 routers): 4 (4-1) / 2 = 6 sessions. Member AS 2 (3 routers): 3 (3-1) / 2 = 3 sessions. Member AS 3 (3 routers): 3 (3-1) / 2 = 3 sessions. Total iBGP sessions = 6 + 3 + 3 = 12.
2. eBGP sessions (between member ASs): The 3 member ASs are fully meshed. 3 (3-1) / 2 = 3 sessions. Total sessions = 12 (iBGP) + 3 (eBGP) = 15.

A. This value only represents the sum of all iBGP sessions within the member ASs, omitting the required eBGP sessions between them.
B. This is an incorrect calculation and does not correspond to any logical combination of iBGP or eBGP sessions in this topology.
C. This is an incorrect calculation and does not correspond to any logical combination of iBGP or eBGP sessions in this topology.

1. Nokia 7750 SR OS 22.10 R1 Unicast Routing Protocols Guide, Section: BGP Confederations. Document ID: 3HE 17918 AAAD TQZZA Edition 01. This guide states, "Within a member AS, BGP operates in the same way as it does in a non-confederated AS. Routers have iBGP sessions with all other routers in the same member AS... Routers in different member ASs have eBGP sessions with each other." This confirms the need to calculate both iBGP and eBGP sessions.

2. RFC 5065: Autonomous System Confederations for BGP, Section 3: Operation. This standard specifies the peering relationships: "Within a member-AS, IBGP is used to distribute routing information... The peering between member-ASs is EBGP." This provides the foundational basis for the calculation methodology.

3. Computer Networking: A Top-Down Approach, 8th Edition, by J. Kurose and K. Ross, Section 5.6.3: BGP. While a general textbook, university-adopted editions describe the full-mesh iBGP requirement (n(n-1)/2 sessions) and how confederations partition this problem, establishing the principles used in the calculation.