I not long ago posted a site about prior blogs I’d composed bearing on SD-Access/DNA Heart style and design and some implementation specifics.

Cisco has documented implementations properly. Even so, what they have looks considerably more focused on one-web-site topics and more on implementation and driving the GUI than style. My prior blogs go into some of the other topics you possibly have to have to consider when creating and arranging for multi-web site SD-Entry.

And I believe that there are some overall style and design thoughts that truly ought to be portion of your pre-purchase and pre-deployment setting up.

As I pointed out in the recent weblog, NetCraftsmen has just lately experienced an upsurge in SD-Entry style and deployment operate. The style and design discussions have revisited many of the themes from my prior blogs and operate.

I’m quite happy that:

  1. Most of the design and style matters I recognized have occur up again, i.e., weren’t solitary-purchaser difficulties, specially the ones I have not observed Cisco truly mentioning.
  2. No new matters have surfaced, despite the fact that I may have a new tactic to some of them.
  3. Certainly, there are some rather-associated matters, like ISE and survivability, that I didn’t create about previously.

As a consequence of the new do the job, I have uncovered myself spelunking as a result of my aged blogs (and inside/shopper-struggling with paperwork) in assist of that. To my relief, my prior blogs and written content feel to be holding up rather perfectly as points have developed.

This web site is the start of a achievable series revisiting some of the style and design matters and similar conversations that have come up.

What Should be a Website?

Yeah, this didn’t really get coated just before. What I wrote was far more of a catalog of kinds of websites. Borders, edges, etcetera.

Wherever some challenges may well appear in is in using your current community and choosing which parts of it need to be websites. Fantastic hierarchical modular structure can play a position in that. Staff, staff mobility, and security boundaries can also perform a role.

Generally, I want a web page to be bodily contiguous or approximately so. So, a site could be:

  • A solitary setting up, compact or huge, probably with many floors.
  • Portion of a setting up, when there is a desire for apparent stability or performance separation (division) (e.g., community security and/or contact center), knowledge heart, team, etcetera. For case in point, a community library within a metropolis or county developing could possibly be a web page individual from the rest due to different funding and/or safety prerequisites.
  • Almost certainly NOT a full multi-creating campus

When there is one particular or two Male or WAN hyperlinks out of a constructing or a small team of properties going to the relaxation of the network, that feels to me like the constructing ought to be a independent web site.

Coming at this in a diverse way, I’ve been a strong believer in hierarchical design and style for decades. So, my preference is for a backbone-leaf or distribution-accessibility switching composition to be a website. Three amounts of switching are alright, way too, as a person website, in rational scaling bounds.

Any domain with VLANs spanning it is a candidate as a internet site. Exception: huge L2 VLAN spans, which are a Really Poor (and historic) Style solution.

From this perspective, L3 switching, or routers generally type the edge of the web site.

And acquiring Male/WAN routed one-way links that are NOT element of a switched cloth can be A Good Point in an SD-Accessibility structure – they can be underlay. See down below.

What’s the objective of carving out web pages?

  • A web-site need to have a effectively-contained geography with Man/WAN interconnections.
  • Widespread macro and micro-segmentation desires (though many web pages can share a typical scheme for all those).
  • Spots with key dissimilarities in purpose or security desires perhaps must be distinct internet sites.
  • In general, keeping down the selection of web-sites simplifies developing and maintaining points. But commonly, in the absence of WAN L2 or other issues, distinctive geographic places ought to in all probability be different web pages for SD-Entry reasons.

An Case in point for Discussion

Suppose you have 3 adjacent properties in a distinctive actual physical area, not too huge, whose exterior connections go via a shared pair of L3 switches. Say just about every making has two or four uplinks from a creating distribution switch pair to the L3 switches.

Should really that be a person site or a few?

My reply: Sure. Both. It depends.

Questions that appear to intellect:

  • Do persons shift around amongst the properties? Out of doors wireless or any network concerning the buildings (like enclosed corridors or what ever)?
  • Do you require to distinguish between the properties as much as machine addressing? (Fairly simpler with different internet sites.)
  • Are there safety or other distinctions, or are they just 3 structures with identical position roles, etcetera., throughout all 3?


The underlay ought to be contiguous. It delivers forwarding concerning websites and also external border websites/info facilities/and so on. You don’t actually want to be doing that with traversal of some internet site smack in the center of your VXLAN tunnels.

SD-Access SDA-Transit can deal with routing among web pages in excess of such an underlay in a scalable way.

If you like VRF-Lite, you can do that for underlay as IP Transit. Be informed that it does not scale at all very well if you are going to have a lot more than a few of VRFs in a multi-web-site style and design. There is also a new technologies vs. comfort zone aspect lurking listed here.

External Border Websites

If you have Online connections, they will probable be at 1 or two “External Border Sites” with (technically speaking) IP Transit connections from some SDA border routers to the fusion firewall complexes, etcetera.

If these web pages are also information centers, as they often are, so substantially the better.

If the data facilities are different, then some dialogue is wanted. Do you will need your VRFs to increase to the data facilities? Are they also likely to have fusion firewalls in them?

And are both equally information facilities connected to both Web-related sites? If not, that mildly complicates routing.

I would hope that if you intend exterior border web-site redundancy, the underlay connects other websites to the exterior border web pages with redundancy and no typical failure points. If not, then maybe you are living with the SPOFs (single position of failure(s)) though preparing for superior dual-homing. Assuming that can be completed in a charge-effective manner.

If that’s not possible, I’d have to see the particular scenario. Generally, the cabling is the problem, with the price to remediate the deficiency of redundancy in a campus or metro environment is the critical concern.


You could not locate deciding on web-sites ex-web-site-ing (groan above undesirable pun here), but undertaking it properly can pay back off in simplicity of being familiar with, diagramming, building out, and troubleshooting an SD-Obtain network.


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