XS-AA-48X1-4X25-ACC
Access & Aggregation48x1G RJ45 access switch with 4x25G uplinks for campus edge, SMB, and enterprise access deployments.
- 210Gbps
- 510Mpps
Overview
MC-LAG allows two physical switches to present an active-active link aggregation interface to a downstream device. In campus networks, it is commonly used between access and aggregation layers to provide device redundancy while keeping uplinks active.
STP remains relevant because many campus environments still carry bridged segments, legacy devices, or unmanaged edge loops. The design goal is to use MC-LAG for resilient forwarding while keeping STP as a controlled safety boundary.
Reference Topology
Access switch or downstream device
| |
v v
xSONiC Agg A <----> xSONiC Agg B
| peer link |
+------ campus core-+The access device sees a single logical bundle. The aggregation pair maintains peer state over a dedicated peer-link and keepalive path.
Design Components
| Component | Purpose | Design Requirement |
|---|---|---|
| Peer-link | Synchronizes state between MC-LAG peers. | Dedicated, redundant, and monitored. |
| Keepalive | Detects peer availability. | Physically separate from peer-link where possible. |
| Member links | Carry downstream bundled traffic. | Same VLAN and LAG policy on both peers. |
| STP boundary | Protects bridged segments. | Root placement and edge-port policy must be deliberate. |
MC-LAG and STP Interaction
| Situation | Risk | Recommended Handling |
|---|---|---|
| Access switch dual-homed to aggregation pair | Loop or blocked uplinks if STP and LAG disagree. | Use MC-LAG as the forwarding construct; keep STP predictable. |
| Legacy Layer 2 segment attached to access | Unexpected topology changes. | Use edge-port and BPDU guard policy where appropriate. |
| Peer-link failure | Split-brain or inconsistent forwarding. | Define fail-safe behavior and monitor keepalive state. |
| VLAN mismatch across peers | Blackholing or asymmetric forwarding. | Automate and audit VLAN/LAG consistency. |
Failure Scenarios
| Failure | Expected Behavior | Test |
|---|---|---|
| Single member link failure | Traffic remains on surviving member. | Pull one access uplink during low-risk window. |
| Aggregation switch reboot | Downstream bundle remains reachable through peer. | Reboot one peer and monitor convergence. |
| Peer-link failure | System enters protected behavior. | Confirm no loop or duplicate forwarding occurs. |
| STP topology change | Network reconverges without large blast radius. | Trigger controlled edge event and review logs. |
Deployment Checklist
- Define aggregation peer pair, peer-link, and keepalive path.
- Configure downstream LAG consistently on both peers.
- Align VLANs, gateway behavior, and access policy.
- Place STP root intentionally for any bridged domains.
- Enable protections such as BPDU guard on true edge ports.
- Test member-link, peer-link, keepalive, and chassis failure cases.
xSONiC Platform Fit
XS-AA aggregation and core models are a natural fit for resilient campus distribution blocks. Higher-density 25G, 100G, and 400G platforms can serve large buildings or campus cores where access closets need active-active uplinks and predictable recovery.
