Opinions on Collapse core or tier 3 architecture for an HQ LAN? When do you switch from tier 2 to tier 3?

[sthomson35]

In my particular case, I'm designing a network for an HQ of an Ice cream company. The building is limited to about 500 drops split up between four IDF So I was debating whether to do a tier 2 or tier 3 setup. This got me thinking about where is the gray area or delineation where to use one vs the other.

I looked into the design guide and while I found interesting information, I didn't find anything that gave numbers, company size, etc, as hints for when to use one or the other. So I just wanted your opinions on the matter, on what would you use in the above example?

https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Campus/cisco-campus-lan-wlan-design-guide.html

[Richard Burts]

There are many factors to consider when doing a network design for a HQ. Certainly size of the company and therefore size of the network are important. You also would consider the possibility of growth of the network, complexity of the network, whether there are parts of the company that need separation in the network from other parts. And I think that you should also consider the skill level of the team that will implement the network, and more importantly the skill level of the team that will support the network.

We do not know much about this company. But I am not hearing anything that suggests that the complexity of a 3 tier network design is needed. Based on what we know so far I believe that a 2 tier would be appropriate.

[Leo Laohoo]

---

@sthomson35 wrote:

https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Campus/cisco-campus-lan-wlan-design-guide.htmll

---

This link to the Design Guide does not fit your requirement because it is a design for a LAN when WLAN is being "considered".   

---

@sthomson35 wrote:

I looked into the design guide and while I found interesting information,

---

If you don't know what you're doing, I strongly recommend you get a professional integrator to do it for you.  Doing a network for an HQ (an HQ, for goodness sake!) is no laughing matter.  It can make-or-break your reputation.  

[sthomson35]

Leo,

I'm in training, and this is a fictional network of which we practice shopping / creating a BOM, choosing/justifying a design, creating an LLD, etc.

[Joseph W. Doherty]

Perhaps the best reason for moving from 2 tier to 3 tier (or 1 tier to 2 tier), is, I believe, the primary reason these architectures came into being, because the hardware cannot handle the size of your network w/o adding another layer. Understand there are other subtle design reasons (beyond the excellent ones mentioned by Rick) for adding layers when the size of the network doesn't require it, or when the physical plant requires it, but the 2 tier and 3 tier models were especially needed when L3 was software based (and very slow compared to L2) and often had low port density per device too (at least in ye olde days).

For example, consider your mention needing to support 500 drops, and ignoring the physical plant and your mention of having four IDFs, physically that could be easily handled by a tier 1 design using an "old" 6513-E, having 528 non-PoE copper gig ports, with dual sup2Ts (using eleven 6848 line cards with DFC4s).

If your IDFs are L3 capable, being only four, another possible tier 1 design might be having some mesh topology between them. Or, you might have a central L2 "core" device that acts as a "hub" between your IDFs (unsure such a L2 "hub" would be considered a tier 1 or tier 2 design).

More common, though, would be a L3 core that connects to your IDFs, which often might be L2, but could also be L3. This design, though, would be considered tier 2, and probably all you need. (BTW, consider, again, the prior "old" 6513-E, with sup2T, can support eleven 8 and/or 16 10g port line cards - that might lent itself to a rather large tier 2 topology.)