Juniper JUNOS OS 10.3 - SOFTWARE Manual page 1639

Table 216: Components of the Topology for Configuring MSTP on EX Series Switches (continued)
Property
Switch 3
Switch 4
VLAN names and tag IDs
MSTIs
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The following ports on Switch 3 are connected in this way:
is connected to Switch 1
ge-0/0/26
is connected to Switch 2
ge-0/0/28
ge-0/0/24 is connected to Switch 4
The following ports on Switch 4 are connected in this way:
is connected to Switch 1
ge-0/0/19
is connected to Switch 3
ge-0/0/23
, tag
voice-vlan 10
, tag
employee-vlan 20
, tag
guest-vlan 30
, tag
camera-vlan 40
1
2
The topology in Figure 36 on page 1542 shows a Common Internal Spanning Tree (CIST).
The CIST is a single spanning tree connecting all devices in the network. The switch with
the highest priority is elected as the root bridge of the CIST.
Also in an MSTP topology are ports that have specific roles:
The root port is responsible for forwarding data to the root bridge.
The alternate port is a standby port for the root port. When a root port goes down, the
alternate port becomes the active root port.
The designated port forwards data to the downstream network segment or device.
The backup port is a backup port for the designated port. When a designated port goes
down, the backup port becomes the active designated port and starts forwarding data.
In this example, one MSTP region,
Switch 4. Within the region, four VLANs are created:
The supports voice traffic and has a VLAN tag identifier of 10.
voice-vlan
employee-vlan supports data traffic and has a VLAN tag identifier of 20.
The supports guest VLAN traffic (for supplicants that fail 802-1X
guest-vlan
authentication) and has a VLAN tag identifier of 30.
The camera-vlan supports video traffic and has a VLAN tag identifier of 40.
The VLANs are associated with specific interfaces on each of the four switches. Two
MSTIs, and , are then associated with the VLAN tag identifiers, and some MSTP
1 2
parameters, such as cost, are configured on each switch.
Chapter 65: Examples of Spanning-Tree Protocols Configuration
, contains Switch 1, Switch 2, Switch 3, and
region1
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