GE T1000, Technical Manual

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Chapter 4
– Functions
GE Reason Switches
86 REASON SWITCHES-TM-EN-3
At the end of the process, egress rules will determine if the switch will maintain or
discard VLAN information.
If it is required to maintain 802.1Q, all frames will leave the switch tagged including
those which have come without tag information, which will leave the switch with the
Port VLAN identifier (PVID) of the incoming port. 802.1Q frames will leave the switch
as it comes.
If it is required to discard all 802.1Q information on the frame, then all frames will
leave the switch untagged, including those which have come with tag information.
Besides the egress filtering of 802.1Q frames, Reason Switches have a third option on the egress filtering: discard information
only from PVID frames. If used, untagged frames that were tagged on PVID will leave the switch untagged, and tagged frames
will leave the switch tagged. Thus, tagged and untagged frames can leave the switch as they come.
9.5 Reason Switches Operation
The Reason Switches are VLAN-aware equipment and its operation allows the use of
traffic segregation as transparent bridge, using 802.1Q tagging. When using VLAN
function, there are some terms and definitions that are used in Reason Switches that
must be understood to a correct configuration.
Reason Switches operate only in VLAN-aware mode, which all traffic is treated in a
VLAN concept. Tagged VLAN will be redirected to the VLAN it belongs, and untagged
traffic will be redirected to the VLAN set in Port VLAN. At the egress, by default,
untagged incoming frames will be forwarded without VLAN tag, as it has come to the
switch.

Port Operation Mode:
Operation mode can be defined as Access, Trunk or Hybrid port.
Access port is used when legacy equipment is connected. Legacy equipment may be
VLAN-unaware equipment and customer VLAN tag equipment, such as IEDs
equipment. These ports will tag untagged ingress traffic with the VLAN Port number
and forward the traffic into this VLAN. When incoming frames have VLAN
information, the frame will be directed to the specified VLAN. At the egress, the tag
used internally by the switch to direct untagged frames will be removed
Access ports are always defined as C-Ports, permit tagged and untagged incoming frames. All frames are untagged at the
egress. Only VLAN port is allowed to traffic. Forbidden VLAN at the ports and egress tagging is user configurable.
Trunk ports accept VLAN tagged frames from many VLAN. These ports permit the
ingress of VLAN-tagged frames and will maintain its tag in the egress. Otherwise, the
user must configure which VLAN the trunk port will accept or not. These ports can be
member of more than one VLAN, limited by maximum number of VLAN permitted
(4,095 VLAN). Incoming data from a not allowed VLAN will be discarded at the ingress
process in the switch. By default, Trunk ports allow to traffic all VLAN range (1
–
4,095). Trunk ports are generally ports connected to switches or IED that send data to
more than one VLAN, such as merging units (one VLAN for GOOSE data and another
one for Sampled Values data).