Switching and aggregation
Switching and aggregation
This domain tests Layer 2 service delivery on Nokia SR OS: Ethernet ports, LAG/MC-LAG, SAPs, SDPs, Epipe/VPLS, EVPN, and spanning tree in aggregation designs.
Core rules
- A SAP binds a service to a port/VLAN, for example 1/1/1:100. An SDP carries service traffic between PEs over MPLS; spoke SDPs use split-horizon to prevent loops, while mesh SDPs allow any-to-any connectivity.
- LAG bundles links with LACP. MC-LAG spans two peers with a shared LACP system ID and MC-LAG ID, providing active/active access.
- Epipe is point-to-point; VPLS is multipoint bridged; VPRN is an IP/MPLS VPN. VPLS can use BGP-AD or EVPN for auto-discovery.
- MSTP root selection uses the lowest bridge priority, then the lowest MAC address. Keep provider service SAPs free of unwanted BPDUs.
Worked example
Two 7750 SR PEs connect an access switch. PE-A has SAP 1/1/1:100 and PE-B has SAP 1/1/2:100. To extend VLAN 100 between sites, configure an Epipe with a SAP on each PE and a spoke SDP from PE-A to PE-B. The VC-ID must match on both ends, and service MTU must match. If a second path exists, split-horizon on the spoke SDPs blocks the loop.
Traps
- Service MTU mismatch silently drops large frames.
- SAP encapsulation must match the tag: dot1q versus QinQ.
- MC-LAG requires consistent LACP keys and no STP on the MC-LAG.
- VPLS MAC learning is per-service, not global.