Specifications

9-36
Cisco ONS 15454 Installation and Operations Guide, R3.2
March 2002
Chapter 9 Ethernet Operation
E Series VLAN Support
Caution If a CARLOSS alarm repeatedly appears and clears on an Ethernet manual cross-connect, the two
Ethernet circuits may have a circuit-size mismatch. For example, a circuit size of STS-3c was configured
on the first ONS 15454 and circuit size of STS-12c was configured on the second ONS 15454. To
troubleshoot this cause of the CARLOSS alarm, refer to the Alarm Troubleshooting Chapter of the Cisco
ONS 15454 Troubleshooting and Maintenance Guide.
9.6 E Series VLAN Support
Users can provision up to 509 VLANs with the CTC software. Specific sets of ports define the broadcast
domain for the ONS 15454. The definition of VLAN ports includes all Ethernet and packet-switched
SONET port types. All VLAN IP address discovery, flooding, and forwarding is limited to these ports.
The ONS 15454 802.1Q-based VLAN mechanism provides logical isolation of subscriber LAN traffic
over a common SONET transport infrastructure. Each subscriber has an Ethernet port at each site, and
each subscriber is assigned to a VLAN. Although the subscriber’s VLAN data flows over shared circuits,
the service appears to the subscriber as a private data transport.
9.6.1 E Series Q-Tagging (IEEE 802.1Q)
IEEE 802.1Q allows the same physical port to host multiple 802.1Q VLANs. Each 802.1Q VLAN
represents a different logical network.
The ONS 15454 works with Ethernet devices that support IEEE 802.1Q and those that do not support
IEEE 802.1Q. If a device attached to an ONS 15454 Ethernet port does not support IEEE 802.1Q, the
ONS 15454 only uses Q-tags internally. The ONS 15454 associates these Q-tags with specific ports.
With Ethernet devices that do not support IEEE 802.1Q, the ONS 15454 takes non-tagged Ethernet
frames that enter the ONS network and uses a Q-tag to assign the packet to the VLAN associated with
the ONS network’s ingress port. The receiving ONS node removes the Q-tag when the frame leaves the
ONS network (to prevent older Ethernet equipment from incorrectly identifying the 8021.Q packet as an
illegal frame). The ingress and egress ports on the ONS network must be set to Untag for the process to
occur. Untag is the default setting for ONS ports. Example #1 in Figure 9-29 illustrates Q-tag use only
within an ONS network.
With Ethernet devices that support IEEE 802.1Q, the ONS 15454 uses the Q-tag attached by the external
Ethernet devices. Packets enter the ONS network with an existing Q-tag; the ONS 15454 uses this same
Q-tag to forward the packet within the ONS network and leaves the Q-tag attached when the packet
leaves the ONS network. Set both entry and egress ports on the ONS network to Tagged for this process
to occur. Example #2 in Figure 9-29 illustrates the handling of packets that both enter and exit the ONS
network with a Q-tag.
For more information about setting ports to Tagged and Untag, see the “Provision Ethernet Ports for
VLAN Membership” procedure on page 9-39.