RSTP ( Rapid STP , Rapid spanning tree protocol , fast spanning tree protocol ), aka IEEE 802.1w-2001 and IEEE 802.1D-2004, is a version of the STP protocol with accelerated tree reconfiguration used to eliminate loops (eliminating duplicate routes) in Ethernet switch connections with redundant lines.
Content
Comparison with STP
Compared to STP , the time needed to build the topology, as well as the time to restore network health, has decreased.
Principle of Operation
The principle of operation is generally similar to STP: a root switch is selected, then each switch involved in building the tree looks for the shortest route (taking into account the channel bandwidth) to the root switch through neighboring switches (or directly). Lines that do not fall into the route are put on hold and are not used for data transfer while the main lines are operating. In case of failure of the main lines, the waiting lines are used to build an alternative topology, after which one of the lines becomes active, and the rest continue to be in standby mode.
Port States
- Discarding
- Learning
- Forwarding
Port Roles
- Root is the unhindered port-to-root switch communication that has the least cost of linking to the root switch.
- Designated - unhindered port communication to the entire LAN segment that does not contain a root switch.
- Alternate - an alternative link to the root switch, different from the used "Root" port. Regular traffic on the port is blocked.
- Backup - a spare / backup link to the LAN segment that provides the LAN segment with a link to the root switch, which is more expensive than the “Designated” port. Regular traffic on the port is blocked.
- Disabled - Not strictly defined by the STP standard, the administrator can manually disable the port.
Link Types
- Shared - port operating in Half Duplex mode
- Point-to-Point - a port that works in Full Duplex mode.
Edge Port
Edge Port - a port connected to the end device on which there is no possibility of creating a loop structure. Features of this port are:
- Transition from Discarding to Forwarding , skipping Learning ;
- The port should work in Full Duplex mode and be Point-to-Point .
The spanning-tree portfast command is used to activate this port mode on Cisco equipment .
Sources
- Alexander Filimonov - construction of multiservice Ethernet networks, BHV-Petersburg, 2007 ISBN 978-5-9775-0007-4