Layer 2 and Layer 3 Networking on CX 10000
This domain tests solid data center L2/L3 fundamentals as implemented in AOS-CX. On the L2 side, understand VLANs, access versus trunk ports, native VLAN behavior, spanning tree (MSTP/RPVST interop), loop protection, and why modern data centers favor L3 underlay plus EVPN over large L2 domains. Know VSX (multichassis LAG) at a conceptual level: two switches present an active-active pair, with inter-switch-link and keepalive.
On the L3 side, be comfortable with interface configuration, SVIs, routed ports, static routes, and OSPF/BGP for underlay reachability. Understand ECMP, ARP/ND behavior, and how anycast gateways (distributed L3) let every leaf act as the default gateway for its attached hosts - critical for avoiding tromboning in a VXLAN fabric.
Traps:
- Confusing VSX roles (primary/secondary) with active/standby - VSX is active-active for data forwarding.
- Assuming a physical routed port and an SVI behave identically for all features.
- Forgetting that anycast gateway requires consistent MAC/IP across leaves.
- Overlooking MTU on underlay links when VXLAN is added later.
Rule of thumb: if hosts in the same subnet sit behind different leaves, you need distributed anycast gateways, not a single centralized SVI. Worked example: two racks, same /24, each leaf configured with the same anycast IP and MAC as the gateway - a host in rack A reaching a host in rack B routes at the local leaf, then crosses the fabric, with no hairpin to a core gateway. Verify with show ip route and show arp on each leaf.
Also review DHCP relay, VRF-lite separation, and ACL application points.