Configuring Stp Parameters - Foundry Networks Switch and Router Installation And Configuration Manual

NOTE: By default, POS ports are not members of the device's default VLAN (VLAN 1) or of any other VLAN.
NOTE: A POS port cannot be added as an untagged port to any VLAN.
A single POS link can multiplex and demultiplex traffic from different clients while keeping each client's traffic
within the client's own Layer 2 broadcast domain (port-based VLAN). The POS port on the send side of the link
sends packets with different tags to the POS port on the receive side. The port on the receive side forwards the
packets based on the VLAN tag. Thus, on the receive side each packet is forwarded only to the Ethernet ports in
the same VLAN as the client.
To configure a POS port for Layer 2 switching, use the following CLI method.
USING THE CLI
To configure a POS port for Layer 2 switching, enter a command such as the following:
BigIron(config)# vlan 10
BigIron(config-vlan-10)# tagged pos 2/1
These commands change the CLI to the configuration level for port-based VLAN 10, then add POS port 2/1 to the
VLAN as a tagged port. You must add the port as a tagged port. You cannot add the port as an untagged port.
Syntax: vlan <vlan-id> [by port]
Syntax: tagged pos <portnum> [to <portnum> | pos <portnum>]
NOTE: This example assumes that port-based VLAN 10 has already been configured. If the VLAN is not
configured, use the command vlan 10 by port.
To verify the VLAN configuration for all the VLANs, enter the following command at any level of the CLI:
BigIron(config)# show vlan
To view all the VLANs configured for a specific POS port, enter a command such as the following at any level of
the CLI:
BigIron(config)# show vlan pos 2/1

Configuring STP Parameters

The following STP features are supported on Layer 2 POS ports:
• Standard STP parameters – All the standard bridge and port parameters supported on Ethernet ports also
are supported on POS ports.
• Single-instance STP – All ports that are members of VLANs that have STP enabled are members of a single
BPDU broadcast domain, and thus share a common STP root bridge. However, the VLANs continue to be
separate broadcast domains for other types of Layer 2 traffic.
• Fast Uplink Span – The Fast Uplink feature enhances STP performance for wiring closet switches with
redundant uplinks. Convergence following a transition from an active link to a redundant link takes around
four seconds, instead of the STP's default convergence time of 30 seconds. Convergence consists of both
the listening and learning states.
NOTE: Fast Port Span applies only to ports that are connected to end hosts, not to Layer 2 POS configurations,
and therefore is not supported.
Changing a POS Port's Path Cost
When selecting among multiple links to the root bridge, STP chooses the link with the lowest path cost and blocks
the other paths. Each port type has a default STP path cost, listed in Table 6.1.
December 2000
Using Packet Over SONET (POS) Modules
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