LEARN. PRACTICE. GROW.Concept and mechanism
An IPv6 link-local address identifies communication within its link. It is not a global address for crossing routers to a remote network. The same value can exist on different links, so interface context matters. When analyzing a capture, distinguish source, destination, and scope before looking for a route. Avoid carrying IPv4 broadcast assumptions into IPv6. Configuration can include several addresses on one interface, and choosing the wrong source can produce a test that does not represent actual application traffic.
Guided application
A switch dynamically learns the source MAC associated with the port and VLAN where a frame arrived. It uses the destination for forwarding lookup, not for learning source location. The table changes as devices move and entries age. A VRF instead separates routing tables: isolated instances can use overlapping addresses without sharing one table. During an incident, record VLAN, VRF, and interface with each observation. A route found in the global table does not prove it exists in the service’s VRF; separation also does not authorize interconnecting environments.
When investigating 10.0.0.7 in a shared environment, identify the VRF first. For fe80::1, identify the link before selecting the neighbor.
Common pitfalls
Querying the wrong table; learning MAC from destination; assuming link-local is global; confusing isolation with connectivity.
Related topics: VLANs, trunks, and access protection · Routing, OSPF, and redundant gateways
A network observation needs interface, VLAN, and routing context.
Reference: Virtual routing and forwarding · 200-301 CCNA v1.1