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Tagged VLANs
To create multiple VLANs that span two switches in a port-based
VLAN, a port on Switch 1 must be cabled to a port on Switch 2 for
each VLAN you want to have span across the switches. At least one
port on each switch must be a member of the corresponding VLANs,
as well.
Figure 4-3
illustrates two VLANs spanning two switches. On Switch 1,
ports 1-4 are part of VLAN Accounting; ports 5 - 8 are part of VLAN
Engineering. On Switch 2, ports 1-4 are part of VLAN Accounting; ports
5 - 8 are part of VLAN Engineering. VLAN Accounting spans Switch 1
and Switch 2 by way of a connection between Switch 1 port 2 and
Switch 2 port 4. VLAN Engineering spans Switch 1 and Switch 2 by
way of a connection between Switch 1 port 5 and Switch 2 port 8
Accounting
1
4
2
3
Switch 1
1
2
3
4
Switch 2
Figure 4-3 Two Port-Based VLANs Spanning Two Switches
Using is configuration, you can create multiple VLANs that span
multiple switches, in a daisy-chained fashion. Each switch must have
a dedicated port for each VLAN. Each dedicated port must be
connected to a port that is a member of its VLAN on the next switch.
Tagging is a process that inserts a marker (called a tag) into the
Ethernet frame. The tag contains the identification number of a
specific VLAN, called the VLANid.
The use of 802.1Q tagged packets may lead to the appearance of
packets slightly bigger than the current IEEE 802.3/Ethernet
maximum of 1,518 bytes. This may affect packet error counters in
other devices, and may also lead to connectivity problems if non-
802.1Q bridges or routers are placed in the path.
AT-9108, AT-8518, AT-8525, and AT-8550 User's Guide
Engineering
8
7
5
6
8
5
6
7
Note
4-5
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