Quick Question on Core Network

Posted on 2008-11-19
Last Modified: 2012-05-05
Just a quick question on Core Layer of the Network...

I am moving routing away from our heavily used core to the Dist layers, which will keep VLANS confined to their requirements.  However Cisco recommends the Core do only Layer 2 and minimal Layer 3, I really cant see how the core can do only layer 2... how would this work?  Also, with Voice, Mgmt etc, each zone of the network would need a different voice and mgmt subnet as you wouldnt want vlans trunked all over the network, as the Cisco Network Model is meant to stop that.

Any advice would be appreciated.
Question by:bromley_college
    LVL 15

    Accepted Solution

    Your Core is the switch between your distribution layer traffic. You don't pass VLAN information because all VLANs terminate at their layer 3 gateway (the distribution layer)
    Cisco is just saying it is a bad idea to make your core layer 3 switch be a default gateway for all your other devices and to get all the vlan traffic.No matter how big a switch it is just a silly idea.

    Author Comment

    That makes it all clear now, thanks for that, I think the way they write it down is can sometimes leave you wondering a bit more than you should.
    LVL 10

    Expert Comment

    Yeah, Cisco is good at that.  Don't get me wrong, they have great products and a wealth of available information; but they've always excelled at taking a somewhat complex topic and making it seem far more complicated.
    Maybe this is a contributing factor to the value of Cisco certs.

    LVL 15

    Expert Comment

    Did you have any questions regarding my explanation? Let me know.

    Author Comment

    Hi bkepford

    Your explanation is fine, thanks for that.  Since routing will happen at the DIST layer the core will not need to route traffic as the native vlan will pass down to the remote DIST layer should that be the destination.  Obviously some vlans may be trunked across but for now we are getting to the testing phases only, so time will tell.

    Thanks again

    Featured Post

    Free Trending Threat Insights Every Day

    Enhance your security with threat intelligence from the web. Get trending threat insights on hackers, exploits, and suspicious IP addresses delivered to your inbox with our free Cyber Daily.

    Join & Write a Comment

    In the world of WAN, QoS is a pretty important topic for most, if not all, networks. Some WAN technologies have QoS mechanisms built in, but others, such as some L2 WAN's, don't have QoS control in the provider cloud.
    If you're not part of the solution, you're part of the problem.   Tips on how to secure IoT devices, even the dumbest ones, so they can't be used as part of a DDoS botnet.  Use PRTG Network Monitor as one of the building blocks, to detect unusual…
    After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
    Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.

    731 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    16 Experts available now in Live!

    Get 1:1 Help Now