Tag: OTV

[DC] Datacenter Interconnects (DCI, OTV)

Distributed Data center Goals

  • Ensure business continuity
  • Distributed applications
  • Seamless workload mobility
  • Maximize compute resources

Challenges in traditional Layer 2 VPN:

  • Flooding Behavior
    • Unknown unicast for mac propagation
    • Unicast Flooding reaches all sites
  • Pseudo-wire Maintenance
    • Full mesh of Pseudo-wire is complex
    • Head-End replication is a common problem
  • Multi-Homing
    • Requires additional protocols and extends STP
    • Malfunctions impact multipe sites

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[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:

 

Lab V ( Nexus7k, Overlay Transport Virtualization )

OTV: Overlay Transport Virtualization

OTV(Overlay Transport Virtualization) is a technology that provide layer2 extension capabilities between different data centers.
In its most simplest form OTV is a new DCI (Data Center Interconnect) technology that routes MAC-based information by encapsulating traffic in normal IP packets for transit.

  • Transparent workload mobility
  • Business resiliency
  • Superior computing resource efficiencies
DescriptionConfig
Overlay InterfaceLogical OTV Tunnel interfaceinterface Overlay1
OTV Join InterfaceThe physical link or port-channel that you use to route upstream towards the datacenter interconnectotv join-interface Ethernet2/1
OTV Control GroupMulticast address used to discover the remote sites in the control plane.otv control-group 224.100.100.100
OTV Data GroupUsed for tunneling multicast traffic over the OTV in the dataplaneotv data-group 232.1.2.0/24
Extend VLANsVLANs that will be tunneled over OTV.otv extend-vlan 100
Site VLANUsed to synchronize the Authoritative Edge Device (AED) role within an OTV site. otv site-vlan 999
Site IdentifierShould be unique per Datacenter. Used in AED Election.otv site-identifier 0x1

References:

Cisco: OTV Quick Start Guide

Cisco: NX-OS OTV Configuration Guide

Cisco: OTV Best Practices

Cisco: OTV Whitepaper

OTV Encapsulation

OTV adds a further 42 bytes on all packets traveling across the overlay network. The OTV Edge device removes the CRC and 802.1Q fields from the original Layer2 frame. It then adds an OTV Shim Header which includes this 802.1Q field (this includes the priority P-bit value) and the Overlay ID information. It also includes an external IP header for the transport network. All OTV packets have Don’t Fragment (DF) bit set to 1 in the external IP header.

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