[DC] NX-OS – 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:



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