OTV Terminology & Concepts
Overlay Transport Virtualization is IP based method to provide Layer 2 extension between different sites over any transport Infrastructure like Layer2 Transport, Layer 3 transport, MPLS, Internet etc.
OTV provides MAC routing which can exchange the MAC reachability information between devices which are on different sites are reachable via any method of IP connectivity.
As we say that OTV provides MAC reachability over IP network then every Ethernet frame which has to be sent across different sites are encapsulated in to IP packet and is delivered across the network. While using existing IP transport network it reduces the use of establishing Virtual Circuit (Like L2 circuit, VPLS, L2VPN, Black fiber) which are costly.
Following are the benefits of using OTV.
- No need for (EoMPLS) or Virtual Private LAN Services (VPLS) deployment for Layer 2 extensions
- OTV uses any network transport that supports IP reachability between sites.
- Spanning Tree Protocol (STP) isolation is achieved by using OTV.
- Bridge Data Protocol Unit (BPDU) filtering is by default done using OTV
- Unknown unicast is not sent to the overlay, this helps in proper BW utilization.
- Address Resolution Protocol (ARP) optimization with the OTV ARP cache
- OTV provides First Hop Redundancy Protocol (FHRP) isolation
- Any number of sites can be added on same OTV Overlay Network.
To understand properly about how OTV works on existing IP transport environment, let’s understand the OTV terminology.
By using below figure we will figure out OTV different terms.
OTV edge device is the NXOS device which perform OTV functions like:
- Receives the layer 2 packet which needs to be extended to remote location and encapsulate to OTV Frame then then in to IP frame.
- There must be at least two edge device on each site to provide redundancy and resiliency.
- Internal Interface are those interface which receives the layer 2 traffic from DC access layer switch.
- Internal Interface can be access port or trunk port connecting different access layer switch or any ESXi host.
- All Layer 2 Function like STP, Switching, MAC learning are done on Internal Interface.
- Join Interface are those interface which are on OTV edge device and this interface encapsulates the OTV frame to IP packet and send to remote Site.
- Join Interface are L3 Interface or L3 Sub interface on OTV edge device.
- Join Interface are associated to OTV overlay interface which means that the OTV frame will use this Join interface to traverse to IP transport to reach to remote site.
- Join Interface discovers the other OTV edge devices.
- After discovery of another OTV edge device, it forms the OTV adjacencies with other OTV edge device
- Join interface is used to send and receive the MAC reachability information.
- Join interface is used to send and receive the unicast and multicast traffic.
- Once Internal interface forwards which is to destined for remote site Overlay interfaces encapsulates the Layer 2 frame which are to be extended to OTV frame.
- This is logical interface, which after encapsulating the Layer 2 frame to OTV frame forwards it to respective Join interface for IP routing.
OTV Function Consideration:
For sending data traffic or Layer 2 traffic over IP transport which is destined for remote sites, OTV build the Control plane and then using control plane data is being sent.
OTV work on two types on Infrastructure:
- Multicast infrastructure
- Unicast Infrastructure
So we will learn how unicast / Multicast data flow on Multicast Infrastructure and also we will learn how unicast / Multicast data flow on Unicast Infrastructure