Dual Layer Spanning Trees - Lucent Technologies Cajun P220 Operation Manual

Dual Layer Spanning Trees

Spanning trees are an IEEE 802.1 standard which provides distributed routing over
multiple LANs connected by bridges.
There are three spanning tree models:
Single IEEE 802.1D spanning tree
Spanning tree per VLAN
Optimized "per-VLAN" spanning trees using a scalable, two-layer spanning tree
approach
Note: All models interoperate with legacy IEEE 802.1D bridges and switches.
Dual layer spanning trees provide two very important capabilities:
Smaller spanning tree domains means much faster convergence during spanning
tree reconfiguration.
Per-VLAN operation enables you to use more of the available bandwidth when you
have redundant links. A particular link can be blocked on one VLAN, but still
forward packets on another.
Cajun P550/P220 Switch Operation Guide
Figure 2-3. Trunking Translation
Trunking Translation:
Frame
Format:
•"Clear"
•IEEE
Frame Format:
802.1Q
"Normal" - Ethernet
•Multilayer
or 802.3 with valid
•3Com
CRC
Overview of the P220 Gigabit Switch Family
Frame
Format:
•"Clear"
•IEEE
802.1Q
•Multilayer
•3Com
2-7