Mstp Network Example - ZyXEL Communications GS2210-8 User Manual

Table 55 Advanced Applicat ion > Spanning Tree Prot ocol > St at us: MSTP ( cont inued)
LABEL
Port Role
Designat ed Bridge
I D
Designat ed Port
I D
Designat ed Cost
Root Guard St at e
13.10 Technical Reference
This sect ion provides t echnical background inform at ion on t he t opics discussed in t his chapt er.

13.10.1 MSTP Network Example

The following figure shows a net work exam ple where t wo VLANs are configured on t he t wo
swit ches. I f t he swit ches are using STP or RSTP , t he link for VLAN 2 will be blocked as STP and RSTP
allow only one link in t he net work and block t he redundant link.
Chapter 13 Spanning Tree Protocol
DESCRIPTION
This field displays t he role of t he port in STP .
• Root - A forwarding port on a non- root bridge, which has t he lowest pat h cost and is
t he best port from t he non- root bridge t o t he root bridge. A root bridge does not have
a root port .
• D e sign a t e d - A forwarding port on t he designat ed bridge for each connect ed LAN
segm ent . A designat ed bridge has t he lowest pat h cost t o t he root bridge am ong t he
bridges connect ed t o t he LAN segm ent . All t he port s on a root bridge ( root swit ch) are
designat ed port s.
• Alt e r n a t e - A blocked port , which has a best alt ernat e pat h t o t he root bridge. This
pat h is different from using t he root port . The port m oves t o t he forwarding st at e
when t he designat ed port for t he LAN segm ent fails.
• Ba ck up - A blocked port , which has a backup/ redundant pat h t o a LAN segm ent
where a designat ed port is already connect ed when a swit ch has t wo links t o t he
sam e LAN segm ent .
• D isa ble d - Not st rict ly part of STP . The port can be disabled m anually.
This field displays t he ident ifier of t he designat ed bridge t o which t his port belongs when
t he port is a designat ed port . Ot herwise, it displays t he ident ifier of t he designat ed bridge
for t he LAN segm ent t o which t his port is connect ed.
This field displays t he priorit y and num ber of t he bridge port ( on t he designat ed bridge) ,
t hrough which t he designat ed bridge t ransm it s t he st ored configurat ion m essages.
This field displays t he pat h cost t o t he LAN segm ent t o which t he port is connect ed when
t he port is a designat ed port . Ot herwise, it displays t he pat h cost t o t he root bridge from
t he designat ed port for t he LAN segam ent t o which t his port is connect ed,
This field displays t he st at e of t he port on which root guard is enabled.
• Root - in con sist e n t - t he Swit ch receives superior BPDUs on t he port and blocks t he
port .
• For w a r din g - t he Swit ch unbolcks and allows t he port t o forward fram es again.
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