Switching and Aggregation
This domain covers Layer 2 forwarding and aggregation in Nokia IP networks: 802.1Q VLANs, access versus trunk ports, STP/RSTP/MSTP, LAG and MC-LAG, QinQ, and the Nokia service model used to aggregate customer traffic.
Core rules
- An access port sends frames untagged for one VLAN; a trunk port carries multiple VLANs with 802.1Q tags.
- STP elects a root bridge by lowest priority, then lowest MAC. RSTP converges faster; MSTP maps VLANs to instances for load sharing.
- A LAG bundles links that must match in speed, duplex, MTU, and VLAN membership. LACP negotiates the bundle.
- MC-LAG extends a LAG across two chassis so a dual-homed device can use active-active links without a Layer 2 loop.
- Nokia Epipe is point-to-point Layer 2; VPLS is multipoint Layer 2; IES provides a routed interface into a service.
Worked example
A customer needs transparent 802.1Q transport between two sites and only those two sites. An Epipe with a SAP at each site is the correct service: it forwards the customer’s tagged frames without MAC learning across a multipoint domain. If a third site were added, VPLS would be required. If the customer needed an IP gateway at the provider edge, an IES would be used instead. Choosing VPLS for a two-site point-to-point link adds unnecessary multipoint behavior and MAC learning.
Traps that cost marks
- Mismatching native VLAN or SAP encapsulation on the two ends.
- Assuming a LAG automatically prevents loops without correct STP or MC-LAG design.
- Forgetting MTU when adding QinQ tags.
- Using a VPLS when a point-to-point Epipe is intended.
Key points
- Access untagged, trunk tagged.
- STP root: priority then MAC.
- LAG members must match.
- Epipe point-to-point, VPLS multipoint, IES routed.
- MC-LAG needs coordinated control, not just two LAGs.