So in the traditional Campus Design it used to be Layer 2 from the Access Layer to the Distribution and to the Endpoints, running Layer 3 on the Distribution and the Core, and in most of the cases, you will have a Core/Distribution approach called Collapsed Distribution Core. as shown in the example:
Now moving from that model to a new and recommended approach you can take a look at the Layer 3 or Route Access layer Design, this one has many benefits as follows:
- Simplified Multicast Design.
- Take advantage of the fast convergence over EIGRP or OSPF, no need for crazy STP troubleshooting (Which can get very cumbersome).
- Just routing troubleshooting using the old and cool ping and traceroute tools.
- No need for HSRP at the access since the interfaces are local to the devices (Don’t agree too much with this one since I’m a strong advocate of First-Hop Redundancy Protocols).
Here is a quick image from the Routed Access Layer Design:
I f you are migrating to this approach it is very simple, don’t be scared on the change of images and complicated links, here is a quick summary:
- Remove the Default Gateway from your Access Switch and turn on Routing support (Config# ip routing)
- IP Addressing will keep being the same, so there is no change here.
- Default Gateway will change for endpoints and other devices connected to the switch, so coordinate accordingly your DHCP server in order to make appropriate changes.
- You will still need to use your “Ip Helper” command under the SVI, in case your DHCP is in another VLAN (Which if you are following best practices in a multisite environment, you bet it is in another VLAN!!!)
Information and screenshots obtained from: Cisco Unified Communications System 9.0 SRND under the Network Infrastructure Section:
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/9x/uc9x/netstruc.html#wp1097139
About the Author:
Andres Sarmiento, CCIE # 53520 (Collaboration)
With more than 13 years of experience, Andres is specialized in the Unified Communications and Collaboration technologies. Consulted for several companies in South Florida, also Financial Institutions on behalf of Cisco Systems. Andres has been involved in high-profile implementations including Cisco technologies; such as Data Center, UC & Collaboration, Contact Center Express, Routing & Switching, Security and Hosted IPT Service provider infrastructures.