Configuring VLANs
625
B Trunk B
1900EN#sh trunk a
DISL state: Auto, Trunking: On, Encapsulation type: ISL
Notice in this output that DISL is auto, trunking is on, and ISL is the
VLAN-encapsulation type on trunk links.
To see which VLANs are allowed on a trunked link, use the show trunk
[a|b]
allowed-vlans command. The following example shows the
VLANs allowed on the trunked interface 26.
1900EN#sh trunk ?
A Trunk A
B Trunk B
1900EN#sh trunk a ?
allowed-vlans Display allowed vlans
joined-vlans Display joined vlans
joining-vlans Display joining vlans
prune-eligible Display pruning eligible vlans
<cr>
1900EN#sh trunk a allowed-vlans
1-4, 6-1004
1900EN#
We cleared VLAN 5 in the preceding section, and the output now states
that VLAN 5 is not being included on the trunked link.
Configuring ISL Routing
To support ISL routing on one Fast Ethernet interface, the router's interface
is divided into logical interfaces, one for each VLAN. These are called sub-
interfaces. Since we have four VLANs, we need four subinterfaces. Each one
of the VLANs is a separate subnet, so here is the addressing I want to use:
VLAN 1
default
172.16.10.0/24
VLAN 2
sales
172.16.20.0/24
VLAN 3
marketing
172.16.30.0/24
VLAN 4
mis
172.16.40.0/24
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