[DC] NX-OS – Overlay Transport Virtualization

https://www.quisted.net/arc/datacenterdesign/lab-v-nexus7k-overlay-transport-virtualization/

What is OTV:

• Layer 2 VPN over IPv4
• Used over the DCI to extend VLANs between datacenter sites

OTV was designed for Layer 2 DCI

• Optimizes ARP Flooding over DCI
• Does not extend STP domain
• Can overlay multiple VLANs without complicated design
• Allows multiple edge routers without complicated design

OTV benefits

• Provides a flexible overlay VPN on top of without restrictions for the IP nework
• L2 transports leveraging the transport IP network capabilities
• Provides a virtual multi-access L2 network that supports efficient transport of unicast, multicast and broadcast traffic

OTV Control Plane

• Uses IS-IS to advertise MAC addresses between AEDs
  • “Mac in IP” Routing
• Encapsulated as Control Group Multicast
  • Implies that DCI Must support ASM Multicast
  • Can be encapsulated as Unicast with OTV Adjacency Server

OTV Data Plane

• Uses both Unicast and Multicast Transport
• Multicast Control Group
  • Multicast or Broadcast Control Plane Protocols
  • eg. ARP, OSPF, EIGRP etc
• Unicast Data
  • Normal Unicast is encapsulated as Unicast between AEDs
• Multicast Data Group
  • Multicast data flows are encapsulated as SSM Multicast
  • Implies AED use IGMPv3 for (S,G) joins
• OTV Adjacency Server can remove requirement for Multicast completely
  • Will result in Head End Replication when more than 2 DC’s connected over the DCI

OTV DCI Optimizations

• Other DCI options bridge all traffic over DCI
  • eg. STP, ARP, Broadcast storms etc
• OTV reducdes unnecessary flooding by:
  • Proxy ARP/ICMPv6 ND Cache on AED
  • Assumption is that hosts are bi-directional (not silent)
  • Inital ARPs are flooded, then cache is used
  • Terminating the STP Domain on AED.

OTV Configuration:

License needed: