4.3. L3-Only Designs

4.3. L3-Only Designs

Network designs that leverage IP routing down to Tier 3 of the network have gained popularity as well. The main benefit of these designs is improved network stability and scalability, as a result of confining L2 broadcast domains. Commonly, an Interior Gateway Protocol (IGP) such as Open Shortest Path First (OSPF) [RFC2328] is used as the primary routing protocol in such a design. As data centers grow in scale, and server count exceeds tens of thousands, such fully routed designs have become more attractive.

Choosing a L3-only design greatly simplifies the network, facilitating the meeting of REQ1 and REQ2, and has widespread adoption in networks where large Layer 2 adjacency and larger size Layer 3 subnets are not as critical compared to network scalability and stability. Application providers and network operators continue to develop new solutions to meet some of the requirements that previously had driven large Layer 2 domains by using various overlay or tunneling techniques.