30
MSTP C
ONFIGURATION
MSTP Overview
Spanning tree protocol (STP) cannot enable Ethernet ports to transit their states
rapidly. It costs two times of the forward delay for a port to transit to the
forwarding state even if the port is on a point-to-point link or the port is an edge
port. This slows down the spanning tree convergence of STP.
Rapid spanning tree protocol (RSTP) enables the spanning tree to converge rapidly,
but it suffers from the same drawback as that of STP: all bridges in a LAN share
one spanning tree; packets of all VLANs are forwarded along the same spanning
tree, and therefore redundant links cannot be blocked by VLANs.
As well as the above two protocols, multiple spanning tree protocol (MSTP) can
disbranch a ring network to form a tree-topological ring-free network to prevent
packets from being duplicated and forwarded endlessly in the ring network.
Besides this, MSTP can also provide multiple redundant paths for packet
forwarding and balances the forwarding loads of different VLANs.
MSTP is compatible with both STP and RSTP. It overcomes the drawback of STP
and RSTP. It not only enables spanning trees to converge rapidly, but also enables
packets of different VLANs to be forwarded along their respective paths to provide
a better load-balancing mechanism with redundant links.
MSTP Protocol Data Unit
Bridge protocol data unit (BPDU) is the protocol data unit (PDU) that STP and RSTP
use.
The switches in a network transfer BPDUs between each other to determine the
topology of the network. BPDUs carry the information that is needed for switches
to figure out the spanning tree.
BPDUs used in STP fall into the following two categories:
■
Configuration BPDUs: BPDUs of this type are used to maintain the spanning
tree topology.
■
Topology change notification BPDU (TCN BPDN): BPDUs of this type are used to
notify the switches of network changes.
Similar to STP and RSTP, MSTP uses BPDUs to figure out spanning trees too.
Besides, the BPDUs of MSTP carry MSTP configuration information of the switches.
Basic MSTP
Terminologies
Figure 60 illustrates basic MSTP terms (assuming that MSTP is enabled on each
switch in this figure).
Summary of Contents for Switch 7754
Page 32: ...32 CHAPTER 1 CLI OVERVIEW ...
Page 70: ...70 CHAPTER 5 LOGGING IN USING MODEM ...
Page 76: ...76 CHAPTER 7 LOGGING IN THROUGH NMS ...
Page 86: ...86 CHAPTER 9 CONFIGURATION FILE MANAGEMENT ...
Page 120: ...120 CHAPTER 13 ISOLATE USER VLAN CONFIGURATION ...
Page 126: ...126 CHAPTER 14 SUPER VLAN ...
Page 136: ...136 CHAPTER 16 IP PERFORMANCE CONFIGURATION ...
Page 152: ...152 CHAPTER 17 IPX CONFIGURATION ...
Page 164: ...164 CHAPTER 19 QINQ CONFIGURATION ...
Page 172: ...172 CHAPTER 21 SHARED VLAN CONFIGURATION ...
Page 182: ...182 CHAPTER 22 PORT BASIC CONFIGURATION ...
Page 198: ...198 CHAPTER 24 PORT ISOLATION CONFIGURATION ...
Page 208: ...208 CHAPTER 25 PORT SECURITY CONFIGURATION ...
Page 224: ...224 CHAPTER 27 DLDP CONFIGURATION ...
Page 232: ...232 CHAPTER 28 MAC ADDRESS TABLE MANAGEMENT ...
Page 240: ...240 CHAPTER 29 CENTRALIZED MAC ADDRESS AUTHENTICATION CONFIGURATION ...
Page 280: ...280 CHAPTER 30 MSTP CONFIGURATION ...
Page 348: ...348 CHAPTER 35 IS IS CONFIGURATION ...
Page 408: ...408 CHAPTER 39 802 1X CONFIGURATION ...
Page 412: ...412 CHAPTER 40 HABP CONFIGURATION ...
Page 422: ...422 CHAPTER 41 MULTICAST OVERVIEW ...
Page 426: ...426 CHAPTER 42 GMRP CONFIGURATION ...
Page 480: ...480 CHAPTER 47 PIM CONFIGURATION ...
Page 506: ...506 CHAPTER 48 MSDP CONFIGURATION ...
Page 552: ...552 CHAPTER 51 TRAFFIC ACCOUNTING CONFIGURATION ...
Page 570: ...570 CHAPTER 53 HA CONFIGURATION ...
Page 582: ...582 CHAPTER 54 ARP CONFIGURATION SwitchA arp protective down recover interval 200 ...
Page 622: ...622 CHAPTER 58 DHCP RELAY AGENT CONFIGURATION ...
Page 684: ...684 CHAPTER 61 QOS CONFIGURATION ...
Page 718: ...718 CHAPTER 63 CLUSTER ...
Page 738: ...738 CHAPTER 67 UDP HELPER CONFIGURATION ...
Page 752: ...752 CHAPTER 69 RMON CONFIGURATION ...
Page 772: ...772 CHAPTER 70 NTP CONFIGURATION ...
Page 796: ...796 CHAPTER 72 FILE SYSTEM MANAGEMENT ...
Page 802: ...802 CHAPTER 73 BIMS CONFIGURATION ...
Page 814: ...814 CHAPTER 74 FTP AND TFTP CONFIGURATION ...
Page 830: ...830 CHAPTER 75 INFORMATION CENTER ...
Page 836: ...836 CHAPTER 76 DNS CONFIGURATION ...
Page 852: ...852 CHAPTER 77 BOOTROM AND HOST SOFTWARE LOADING ...
Page 858: ...858 CHAPTER 78 BASIC SYSTEM CONFIGURATION DEBUGGING ...