Cisco ONS 15454 SDH Specifications Page 382

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9-36
Cisco ONS 15454 SDH Installation and Operations Guide, R3.3
May 2002
Chapter 9 Ethernet Operation
E Series VLAN Support
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 SDH 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 SDH Ethernet port does not support IEEE
802.1Q, the ONS 15454 SDH only uses Q-tags internally. The ONS 15454 SDH associates these Q-tags
with specific ports.
With Ethernet devices that do not support IEEE 802.1Q, the ONS 15454 SDH 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 networks 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 9-30 illustrates Q-tag use only
within an ONS network.
With Ethernet devices that support IEEE 802.1Q, the ONS 15454 SDH uses the Q-tag attached by the
external Ethernet devices. Packets enter the ONS network with an existing Q-tag; the ONS 15454 SDH
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 9-30 illustrates the handling of packets that both enter and
exit the ONS network with a Q-tag.
To set ports to Tagged and Untag, see the Provision Ethernet Ports for VLAN Membership procedure
on page 9-39.
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