Cisco CX-FEIP-2TX= Installation and con?guration Specifications download pdf (Page 380)

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Cisco ONS 15454 Installation and Operations Guide, R3.2

March 2002

Chapter 9 Ethernet Operation

E Series Spanning Tree (IEEE 802.1D)

Note If Tagged is chosen, the attached external devices must recognize IEEE 802.1Q VLANs.

Note Both ports on individual E1000-2/E1000-2-G cards cannot be members of the same VLAN.

9.7 E Series Spanning Tree (IEEE 802.1D)

The Cisco ONS 15454 operates spanning tree protocol (STP) according to IEEE 802.1D when an

Ethernet card is installed. STP operates over all packet-switched ports including Ethernet and SONET

ports. On Ethernet ports, STP is disabled by default but may be enabled with a check box under the

Provisioning > Port tabs at the card-level view. On SONET interface ports, STP activates by default and

cannot be disabled.

The Ethernet card can enable STP on the Ethernet ports to allow redundant paths to the attached Ethernet

equipment. STP spans cards so that both equipment and facilities are protected against failure.

STP detects and eliminates network loops. When STP detects multiple paths between any two network

hosts, STP blocks ports until only one path exists between any two network hosts (Figure 9-32). The

single path eliminates possible bridge loops. This is crucial for shared packet rings, which naturally

include a loop.

Figure 9-32 An STP blocked path

To remove loops, STP defines a tree that spans all the switches in an extended network. STP forces

certain redundant data paths into a standby (blocked) state. If one network segment in the STP becomes

unreachable, the spanning-tree algorithm reconfigures the spanning-tree topology and reactivates the

blocked path to reestablish the link. STP operation is transparent to end stations, which do not

discriminate between connections to a single LAN segment or to a switched LAN with multiple

segments. The ONS 15454 supports one STP instance per circuit and a maximum of eight STP instances

per ONS 15454.

Untag The ONS 15454 will tag ingress frames and strip tags from egress frames.

Tagged The ONS 15454 will handle ingress frames according to VLAN ID; egress

frames will not have their tags removed.

Table 9-8 Port Settings (continued)

Setting Description

43388

Redundant path (blocked)

Primary path (forwarding)

1 2 ... 375 376 377 378 379 380 381 382 383 384 385 ... 492 493

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Cisco CX-FEIP-2TX= Installation and con?guration Specifications Page 380