Mixed stp and rstp networks, Spanning tree and vlans, Class 1 laser product – Allied Telesis AT-S88 User Manual
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Chapter 11: STP and RSTP
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Figure 32. Edge Port
A port can be both a point-to-point and an edge port at the same time. It
operates in full-duplex and has no STP or RSTP devices connected to it.
Figure 33 illustrates a port functioning as both a point-to-point and edge
port.
Figure 33. Point-to-Point and Edge Port
Determining whether a bridge port is point-to-point, edge, or both, can be
a bit confusing. For that reason, do not change the default values for this
RSTP feature unless you have a good grasp of the concept. In most
cases, the default values work well.
Mixed STP and
RSTP Networks
RSTP IEEE 802.1w is fully compliant with STP IEEE 802.1d. Your network
can consist of bridges running both protocols. STP and RSTP in the same
network can operate together to create a single spanning tree domain.
If you decide to activate spanning tree on the switch, there is no reason
not to activate RSTP on an AT-FS750/24POE Fast Ethernet Smart Switch
even when all other switches are running STP. The switch can combine its
RSTP with the STP of the other switches. The switch monitors the traffic
on each port for BPDU packets. Ports that receive RSTP BPDU packets
operates in RSTP mode while ports receiving STP BPDU packets operate
in STP mode.
Spanning Tree
and VLANs
The spanning tree implementation in the AT-S88 management software is
a single-instance spanning tree. The switch supports just one spanning
tree. You cannot define multiple spanning trees.
The single spanning tree encompasses all ports on the switch. If the ports
are divided into different VLANs, the spanning tree crosses the VLAN
boundaries. This point can pose a problem in networks containing multiple
VLANs that span different switches and are connected with untagged
ports. In this situation, STP blocks a data link because it detects a data
loop. This can cause fragmentation of your VLANs.
This issue is illustrated in Figure 34. Two VLANs, Sales and Production,
1088
AT-FS750/24POE
24 Port 10/100 Mbps WebSmart Switch
with 2 Combo Uplinks + 12 POE Ports
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PD ON
PD ERROR
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PORT ACTIVITY
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CLASS 1
LASER PRODUCT
SFP
10/100/1000Base-T
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SFP
10/100/1000Base-T
UPLINK PORTS
10/100 PORTS
Point-to-Point and Edge Port
Workstation
(Full-duplex Mode)