Dell 8100 manual Method 1 Portfast, Rstp

Deploying the Dell PowerConnect 8100 with the Cisco Catalyst

RSTP	(Based on IEEE 802.1w) - Rapid STP. A standards-based protocol that is considerably
	faster at network convergence (after a topology change) than its STP predecessor in
	most network implementations. It is the default for the Dell PowerConnect 8100,
	and is compatible with STP.
MST	(Based on IEEE 802.1s) – Multiple Spanning Tree protocol or MSTP. Allows for
	multiple instances of spanning tree across a network. Each instance contains one or
	more VLANs. Enables load balancing of traffic through the network while minimizing
	CPU cycles.
PVST+	Per VLAN spanning Tree. A Cisco proprietary protocol similar to STP that allows
	each VLAN to run its own instance of Spanning Tree. It is available on the Cisco
	Catalyst 6500.
RPVST+	Rapid PVST+. A Cisco proprietary protocol that is considerably faster at network
	convergence (after a topology change) than its PVST+ predecessor in most network
	implementations. It is the default on the Cisco Catalyst 6500.
CST	Common Spanning Tree. A single spanning tree instance for an entire network
	regardless of the number of VLANs on that network.
BPDU	Bridge Protocol Data Unit. Packets that are exchanged between network devices to
	help detect loops in a network.
802.1d	IEEE standard that allows spanning tree ports to be in one of the following states:
	listen, learn, forward, block, or disabled.
802.1w	IEEE standard that allows spanning tree ports to be in one of the following states:
	learn, forward, or discard. Discard replaces listen, block, and disable states. A
	great improvement in convergence speed over 802.1d.
801.1s	IEEE standard that allows for multiple instances of spanning tree across a physical
	bridged network.

Attempting to recover from a failed network device is a common difficulty that arises on a Cisco Catalyst network using RPVST+, when standards-based edge devices are attached in a redundant loop topology. RPVST+ ports from the Cisco Catalyst switch that are connected to the Dell PowerConnect 8100 no longer receive BPDUs from VLANs not in the CST. This causes a delay in network activity until the forward-delay timer expires.

To minimize downtime when using Cisco proprietary protocols (PVST+, RPVST+) together with standard protocols (STP, RSTP) on the Dell PowerConnect switches, additional instruction on the network is required. Below are two common methods to get the job done.

Method 1: Portfast

Ports on the Cisco Catalyst switch that are directly connected to the Dell PowerConnect 8100 can be forced into forwarding state after a network change by using the portfast option. The rapid spanning tree protocols quickly blocks any loops detected in the network during convergence. The block occurs at a location away from the Cisco core network. In this scenario, the link between the Dell PowerConnect switches is blocked. This is the most recommended method.

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