Cisco IT is excited to be hosting its third Data Center Day in Allen, Texas this year on April 14th. Last September, Data Center Day was attended by 144 customers from 75 companies. With registration now open this event is expected to fill up fast! Read More »
VXLAN (IETF RFC7348) has been designed to solve specific problems faced with Classical Ethernet for a few decades now. By introducing an abstraction through encapsulation, VXLAN has become the de-facto standard overlay of choice in the industry. Chief among the advantages provided by VXLAN; extension of the todays limited VLAN space and the increase in the scalability provided for Layer-2 Domains.
Extended Namespace – The available VLAN space from the IEEE 802.1Q encapsulation perspective is limited to a 12-bit field, which provides 4096 VLANs or segments. By encapsulating the original Ethernet frame with a VXLAN header, the newly introduced addressing field offers 24-bits, thereby providing a much larger namespace with up to 16 Million Virtual Network Identifiers (VNIs) or segments.
While the VXLAN VNI allows unique identification of a large number of tenant segments which is especially useful in high-scale multi-tenant deployments, the problems and requirements of large Layer-2 Domains are not sufficiently addressed. However, significant improvements in the following areas have been achieved:
- No dependency on Spanning-Tree protocol by leveraging Layer-3 routing protocols
- Layer-3 routing with Equal Cost Multi-Path (ECMP) allows all available links to be used
- Scalability, convergence, and resiliency of a Layer-3 network
- Isolation of Broadcast and Failure Domains
IETF RFC7348 – VXLAN: A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks
Scalable Layer-2 Domains
The abstraction by using a VXLAN-like overlay does not inherently change the Flood & Learn behavior introduced by Ethernet. In typical deployments of VXLAN, BUM (Broadcast, Unicast, Multicast) traffic is forwarded via layer-3 multicast in the underlay that in turn aids in the learning process so that subsequent traffic need not be subjected to this “flood” semantic. A control-plane is required to minimize the flood behavior and proactively distribute End-Host information to participating entities (typically called Virtual Tunnel End Points aka VTEPs) in the same segment – learning.
Control-plane protocols are mostly employed in the layer-3 routing space where predominantly IP prefix information is exchanged. Over the past years, some of the well-known routing protocols have been extended to also learn and exchange Layer-2 MAC addresses. An early technology adoption with MAC addresses in a routing-protocol was Cisco’s OTV (Overlay Transport Virtualization), which employed IS-IS to significantly reduce flooding across Data Center Interconnects (DCI).
Multi-Protocol BGP (MP-BGP) introduced a new Network Layer Reachability Information (NLRI) to carry both, Layer-2 MAC and Layer-3 IP information at the same time. By having the combined set of MAC and IP information available for forwarding decisions, optimized routing and switching within a network becomes feasible and the need for flood to do learning get minimized or even eliminated. This extension that allows BGP to transport Layer-2 MAC and Layer-3 IP information is called EVPN – Ethernet Virtual Private Network.
EVPN is documented in the following IETF drafts
- draft-sd-l2vpn-evpn-overlay – A Network Virtualization Overlay Solution using EVPN
- draft-sajassi-l2vpn-evpn-inter-subnet-forwarding-03 – IP Inter-Subnet Forwarding in EVPN
Integrated Route and Bridge (IRB) – VXLAN-EVPN offers significant advantages in Overlay networking by optimizing forwarding decision within the network based on Layer-2 MAC as well as Layer-3 IP information. The decision on forwarding via routing or switching can be done as close as possible to the End-Host, on any given Leaf/ToR (Top-of-Rack) Switch. The Leaf Switch provides the Distributed Anycast Gateway for routing, which acts completely stateless and does not require the exchange of protocol signalization for election or failover decision. All the reachability information available within the BGP control-plane is sufficient to provide the gateway service. The Distributed Anycast Gateway also provides integrated routing and bridging (IRB) decision at the Leaf Switch, which can be extended across a significant number of nodes. All the Leaf Switches host active default gateways for their respective configured subnets; the well known semantic of First Hop Routing Protocols (FHRP) with active/standby does not apply anymore.
Summary – The advantages provided by a VXLAN-EVPN solution are briefly summarized as follows:
- Standards based Overlay (VXLAN) with Standards based Control-Plane (BGP)
- Layer-2 MAC and Layer-3 IP information distribution by Control-Plane (BGP)
- Forwarding decision based on Control-Plane (minimizes flooding)
- Integrated Routing/Bridging (IRB) for Optimized Forwarding in the Overlay
- Leverages Layer-3 ECMP – all links forwarding – in the Underlay
- Significantly larger Name-Space in the Overlay (16M segments)
- Integration of Physical and Virtual Networks with Hybrid Overlays
- It facilitates Software-Defined-Networking (SDN)
Simply formulated, VXLAN-EVPN provides a standards-based Overlay that supports Segmentation, Host Mobility, and High Scale.
VXLAN-EVPN is available on Nexus 9300 (NX-OS 7.0) with Nexus 7000/7700 (F3 linecards) to follow in the upcoming major release. Additional Data Center Switching platforms, like the Nexus 5600, will follow shortly after.
- BRKDCT-2404 -VXLAN deployment models – A practical perspective (by Victor Moreno)
- BRKDCT-3378 – Building Simplified, Automated and Scalable Data Center Networks with Overlays (VXLAN/FabricPath) (by Lukas Krattiger)
Do you have appetite for more? Post a comment, tweet about it and have the conversation going … Thanks for reading and Happy Networking!
Today’s IT leaders want more from their data centers – and their technology partners. Customers want their technology partners to work together to deliver integrated solutions that enable business innovation. They can’t be limited by aging infrastructure and legacy platforms. With the end of support for Windows Server 2003 rapidly approaching, Cisco channel partners have an opportunity to help their customers migrate to a modern data center solution based on Cisco UCS and Windows Server 2012 R2.
Microsoft will end support for Windows Server 2003 on July 14, 2015. After this date, security updates will no longer be available and customers will be exposed to significant compliance and security risks. With millions of Windows 2003 servers still in production, channel partners have an opportunity to grow their UCS and Microsoft revenue with value added services including:
- Design and manage the migration of customer environments from Window Server 2003 to Widows Server 2012 and Cisco UCS
- Design and manage server consolidation projects
- Plan, build, and manage the transition to Microsoft Private Cloud on UCS integrated infrastructures
The Lineup: Microsoft, Cisco, and Intel
It’s no secret that tested and tried solutions will lead to a faster time to production, allowing you to stay at the forefront of innovation and, most importantly, stand out from the competition.
The latest in our series of deep-dive examinations, our Microsoft-focused edition of Unleashing IT shows you how three industry leaders are creating integrated solutions to achieve better business outcomes. Read More »
I’d like to give you an inside look at our Allen Data Center and go over how Cisco IT is adopting new technologies and capabilities while at the same time running the business. I’ll answer your top of mind questions and cover topics such as: Read More »