Service Chaining via Cisco Catena

Peter Welcher
Architect, Operations Technical Advisor

This blog is a small follow-up to the Neat Cisco Nexus Features You Might Have Missed blog.

Some Cisco folks pointed me to the “Catena” feature, implemented in some Cisco Nexus 9K and in the Nexus 7K models. Catena is Latin for “chain”.

From one point of view, Catena is locally-configured hybrid OpenFlow. That is, locally-configured specification of over-ride behavior forwarding (or dropping) based on flow specifications.

What Is Catena

Catena lets you build service chains for services from devices that connect to a single datacenter switch. That is, you can force selected traffic through external devices 1, 2, 3, etc. For example; firewall, IPS, IPsec MITM box, whatever.

Here’s a diagram showing what you can do with Catena:

This to a degree generalizes the ITD topic discussed in my prior blog (link above). It is done by modifying TCAM, so you get full performance. Catena uses the notion of device groups: it load balances across devices within configured device groups.

I’ll note that Catena has “transparent” (L2) and routed modes. For more, I’ll Reference the Fine Manual (RTFM) — Nexus 9K version (or see also the Nexus 7K link below).

My Reaction

If you need to selectively forward to or bypass certain devices, Catena could be very handy.

I do need to note that selective forwarding based on more than destination address does complicate things. Factoring in behavior based on source address or source / destination port means more forwarding equivalence classes of traffic, each behaving in their own way. More to understand! This is not necessarily good or bad, it is more to note that using a feature like this adds complexity, and you need to think about managing that complexity.

My Beer Principle likely applies: one beer good, many beers equals headache. Do too much Catena, and you may develop a headache?



Comments are welcome, both in agreement or constructive disagreement about the above. I enjoy hearing from readers and carrying on deeper discussion via comments. Thanks in advance!


Hashtags: #CiscoChampion #TheNetCraftsmenWay #CiscoCatena #CiscoNexus #DataCenter

Twitter: @pjwelcher

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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.


Virgilio “BONG” dela Cruz Jr.

CCDP, CCNA V, CCNP, Cisco IPS Express Security for AM/EE
Field Solutions Architect, Tech Data

Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.


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John is our CTO and the practice lead for a talented team of consultants focused on designing and delivering scalable and secure infrastructure solutions to customers across multiple industry verticals and technologies. Previously he has held several positions including Executive Director/Chief Architect for Global Network Services at JPMorgan Chase. In that capacity, he led a team managing network architecture and services.  Prior to his role at JPMorgan Chase, John was a Distinguished Engineer at Cisco working across a number of verticals including Higher Education, Finance, Retail, Government, and Health Care.

He is an expert in working with groups to identify business needs, and align technology strategies to enable business strategies, building in agility and scalability to allow for future changes. John is experienced in the architecture and design of highly available, secure, network infrastructure and data centers, and has worked on projects worldwide. He has worked in both the business and regulatory environments for the design and deployment of complex IT infrastructures.