Presenter mode

Collapsed core

Walkthrough

Two tiers: access into a collapsed core

Distribution and core roles share one redundant pair. Access dual-homes north; WAN and shared services attach at the collapsed core — there is no separate core tier.

Step 1 / 4

Access switches attach endpoints. The collapsed-core pair aggregates those uplinks, hosts Layer-3 gateways, and connects toward WAN, firewall, and shared services — the separate core tier is omitted on purpose for a small site.

Walkthrough

East–west inter-VLAN via the collapsed core

Hosts in different VLANs meet at Layer-3 SVIs on the collapsed core. Same-VLAN flooding stays local when the L2 design allows; cross-VLAN always climbs to the CC pair.

Step 1 / 4

Host on VLAN 10 and host on VLAN 20 share the campus fabric but not a broadcast domain. Inter-VLAN routing is concentrated on the collapsed-core gateways.

Exact IRB/SVI placement and FHRP pairing are site-specific; this walkthrough is illustrative of the common collapsed-core pattern.

Walkthrough

One collapsed-core member fails

Losing one CC member reduces capacity and HA paths. Dual-homed access should keep forwarding on the surviving member when uplinks and FHRP/routing are designed for that failure.

Step 1 / 4

Both collapsed-core members are forwarding. Access uplinks and services attachments are dual-homed. Capacity and change windows still couple routing and often WAN attachment on this pair.