ENHANCEMENTS TO STP

  1. Cisco's proprietary PortFast takes a port out of STP and leaves it in a forwarding state (spanning-tree portfast). Cisco's proprietary UplinkFast detects a failed root port connection and then places a backup link in a forwarding state (spanning-tree uplinkfast). Cisco's proprietary BackboneFast detects failures on nonconnected interfaces by looking for inferior BPDUs (spanning-tree backbonefast).

  2. In RSTP, an alternate port serves as a secondary root port in case the primary root port fails. It is in a discarding port state unless a failure of the root port or connection occurs, in which case it is moved to a forwarding state. A backup port serves as a secondary designated port in case the primary designated port fails.

  3. To belong to the same MST region, all switches in the region must have the same region name, revision number, and VLAN table mappings.

  4. PAgP uses Desirable and Auto, whereas LACP uses Passive and Active. The mode On enables channeling on an interface, but disables PAgP and LACP.

  5. To form an EtherChannel, all ports must be configured identically. They shouldn't be part of a dynamic VLAN, and port security should be disabled. Only eight interfaces are supported in a channel, but they don't have to be contiguous or on the same module. Use the channel-group command to include an interface in a channel.

  6. UDLD and Loop Guard are used to detect unidirectional connections between switches. UDLD detects wiring problems, and Loop Guard protects against missing BPDUs from neighbors.



BCMSN Exam Cram 2 (Exam Cram 642-811)
CCNP BCMSN Exam Cram 2 (Exam Cram 642-811)
ISBN: 0789729911
EAN: 2147483647
Year: 2003
Pages: 171
Authors: Richard Deal

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