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Path Optimization for LAN Extension: Addressing Suboptimal Routing in Extended Data Centers

This draft discusses the challenges of path optimization for LAN extension across multiple data center locations using VPLS and L3VPN solutions. It highlights two primary problems: suboptimal routing for incoming traffic due to the loss of location semantics in the extended subnet, and suboptimal outgoing traffic routing caused by identical default gateways configured across different locations. The draft proposes solutions that involve creating host routes within the extended subnet and optimizing traffic paths based on proximity to local resources, prompting a discussion on incorporation into existing frameworks.

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Path Optimization for LAN Extension: Addressing Suboptimal Routing in Extended Data Centers

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  1. Path Optimization for LAN Extension • draft-xu-nvo3-lan-extension-path-optimization-00 Xiaohu Xu (Huawei) • Kai Lee (China Telecom) IETF85, Atlanta

  2. Generic Data Center Interconnect Architecture • Assume the existing VPLS solution [RFC4761, RFC4762] is used to achieve LAN extension across multiple data center locations and L3VPN [RFC4364] is used by cloud users to access the computing resources within data centers. • Internet gateway is outside of the scope.

  3. Problem Statement • Problem 1: Suboptimal Routing for Incoming Traffic. • Since the subnet associated with the extended LAN has also been extended across multiple locations, the subnet no longer retains its location semantics. • The incoming traffic from cloud users towards a given server within the extended subnet could travel along suboptimal paths. Advertise a route for the extended subnet to PE-3 Advertise a route for the extended subnet to PE-3

  4. Problem Statement (cont.) • Problem 2: Suboptimal Routing for Outgoing Traffic. • To keep the default gateway of the moved VM unchanged, default gateways of different locations are usually configured with identical IP and MAC addresses (e.g., enable VRRP but filter VRRP messages). • However, the VPLS forwarding path towards the VRRP virtual MAC could be pointed to a default gateway at the remote data center. Virtual IP=X Virtual MAC=Y Virtual IP=X Virtual MAC=Y

  5. Solution Requirements • Solution to Problem 1 • Each default gateway router acting as a L3VPN PE router should be capable of creating host routes for those local servers within the extended subnet and propagating them to remote PE routers at cloud user sites. • Solution to Problem 2 • To ensure the outgoing inter-subnet traffic to be forwarded to a local default gateway in normal cases, the LAN extension solution should be able to select the best route (i.e., the closest one) for a given MAC address (e.g., the VRRP virtual MAC address) among multiple possible routes on the control plane.

  6. Next-steps • Comments and suggestions? • Should the path optimization issue and requirement parts of this draft be incorporated into the problem statement draft and the framework draft respectively? • Or should it be adopted as a companion draft to the PS and Framework drafts?

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