HP 5500 Ei 5500 Si Switch Series Configuration Guide
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70 • Same VLAN-to-instance mapping configuration • Same MSTP revision level • Physically linked together Multiple MST regions can exist in a switched network. You can assign multiple devices to the same MST region. In Figure 20, the switched network comprises four MST regions, MST region 1 through MST region 4, and all devices in each MST region have the same MST region configuration. MSTI MSTP can generate multiple independent spanning tr ees in an MST region, and each spanning tree is mapped to the specific VLANs. Each spanning tree is referred to as a multiple spanning tree instance (MSTI). In Figure 21 , MST region 3 comprises three MSTIs, MSTI 1, MSTI 2, and MSTI 0. VLAN-to-instance mapping table As an attribute of an MST region, the VLAN-to-instance mapping table describes the mapping relationships between VLANs and MSTIs. In Figure 21 , the VL AN-to-instance mapping table of MST region 3 is: VLAN 1 to MSTI 1, VLAN 2 and VLAN 3 to MSTI 2, and other VLANs to MSTI 0. MSTP achieves load balancing by means of the VLAN-to-instance mapping table. CST The common spanning tree (CST) is a single spanning tree that connects all MST regions in a switched network. If you regard each MST region as a device, the CST is a spanning tree calculated by these devices through STP or RSTP. The blue lines in Figure 20 r epresent the CST. IST An internal spanning tree (IST) is a spanning tree that runs in an MST region. It is also called MSTI 0, a special MSTI to which all VLANs are mapped by default. In Figure 20 , M STI 0 is the IST in MST region 3. CIST The common and internal spanning tree (CIST) is a si ngle spanning tree that connects all devices in a switched network. It consists of the ISTs in all MST regions and the CST. In Figure 20 , t he ISTs (MSTI 0) in all MST regions plus the inter-region CST constitute the CIST of the entire network. Regional root The ro ot bridg e of the IST or an MSTI wi thin an MST re g ion i s the re g ional ro ot of the IST or MSTI. B ase d on the topology, different spanning trees in an MST region might have different regional roots. For example, in MST region 3 in Figure 21, the regional root of MSTI 1 is Device B, the regional root of MSTI 2 is Device C, and the regional root of MSTI 0 (also known as the IST) is Device A. Common root bridge The common root bridge is the root bridge of the CIST. In Figure 20 , f or example, the common root bridge is a device in MST region 1.
71 Port roles A port can play different roles in different MSTIs. As shown in Figure 22, an MST region comprises Device A, Device B, Device C, and Device D. Port A1 and port A2 of Device A connect to the common root bridge. Port B2 and Port B3 of Device B form a loop. Port C3 and Port C4 of Device C connect to other MST regions. Port D3 of Device D directly connects to a host. Figure 22 Port roles MSTP calculation involves the following port roles: • Root port —Forwards data for a non-root bridge to the root bridge. The root bridge does not have any root port. • Designated port —Forwards data to the downstream network segment or device. • Alternate port —The backup port for a root port or master port. When the root port or master port is blocked, the alternate port takes over. • Backup port —The backup port of a designated port. Wh en the designated port is invalid, the backup port becomes the new designated port. A loop occurs when two ports of the same spanning tree device are interconnected, so the de vice blocks one of the ports. The blocked port acts as the backup. • Edge port —An edge port does not connect to any networ k device or network segment, but directly connects to a user host. • Master port —A port on the shortest path from the local MST region to the common root bridge. The master port is not always located on the regional root . It is a root port on the IST or CIST and still a master port on the other MSTIs. • Boundary port —Connects an MST region to another MST region or to an STP/RSTP-running device. In MSTP calculation, a boundary port’s role on an MSTI is consistent with its role on the CIST. But that is not true with master ports. A master port on MSTIs is a root port on the CIST. Port states In MSTP, a port can be in one of the following states:
72 • Forwarding —The port receives and sends BPDUs, obtains MAC addresses, and forwards user traffic. • Learning —The port receives and sends BPDUs, obtains MAC addresses, but does not forward user traffic. Learning is an intermediate port state. • Discarding —The port receives and sends BPDUs, but does not obtain MAC addresses or forward user traffic. When in different MSTIs, a port can be in different st ates. A port state is not exclusively associated with a port role. Table 13 lists the por t states that each por t ro l e s u p p o r t s. (A ch e ck m a rk [ √] indicates that the port supports this state, while a dash [—] indicates that the port does not support this state.) Table 13 Port states that differe nt port roles support Port role (ri ght) Root port/master port Designated port Alternate port Backup port Port state (below) Forwarding √ √ — — Learning √ √ — — Discarding √ √ √ √ How MSTP works MSTP divides an entire Layer 2 network into multiple MST regions, which are connected by a calculated CST. Inside an MST region, multiple spanning trees are calculated. Each spanning tree is an MSTI. Among these MSTIs, MSTI 0 is the IST. Like STP, MSTP uses configuration BPDUs to calculate spanning trees. An important difference is that an MSTP BPDU carries the MSTP configuration of the bridge from which the BPDU is sent. CIST calculation The calculation of a CIST tree is also the process of configuration BPDU comparison. During this process, the device with the highest priority is elected as the root bridge of the CIST. MSTP generates an IST within each MST region through calculation. At the same time, MSTP regards each MST region as a single device and generates a CST among these MST regions through calculation. The CST and ISTs constitute the CIST of the entire network. MSTI calculation Within an MST region, MSTP generates different MSTIs for different VLANs based on the VLAN-to-instance mappings. For each spanning tree , MSTP performs a separate calculation process similar to spanning tree calculation in STP. For more information, see Calculation process of the STP algor ithm . In MSTP, a VLAN packet is forwarded along the following paths: • Within an MST region, the packet is forwarded along the corresponding MSTI. • Between two MST regions, the packet is forwarded along the CST. Implementation of MSTP on devices MSTP is compatible with STP and RSTP. Devices that are running MSTP and that are used for spanning tree calculation can identify STP and RSTP protocol packets.
73 In addition to basic MSTP functions, the following functions are provided for ease of management: • Root bridge hold • Root bridge backup • Root guard • BPDU guard • Loop guard • TC-BPDU guard • BPDU drop. Protocols and standards The spanning tree protocols are docu mented in the following standards: • IEEE 802.1d, Media Access Control (MAC) Bridges • IEEE 802.1w, Part 3: Media Access Control (MAC) Bridges—Amendment 2: Rapid Reconfiguration • IEEE 802.1s, Virtual Bridged Local Area Networks—A mendment 3: Multiple Spanning Trees Spanning tree configuration task list Before configuring a spanning tree, you must determine the spanning tree protocol to be used (STP, RSTP, PVST, or MSTP) and plan the device role s (the root bridge or leaf node). Configuration restrictions and guidelines • If GVRP and a spanning tree protocol are enabled on a device at the same time, GVRP packets are forwarded along the CIST. To advertise a certain VLAN within the network through GVRP, be sure that this VLAN is mapped to the CIST when you configure the VLAN-to-instance mapping table. For more information about GVRP, see Configuring GVRP. • The spanning tree configurations are mutually exclusive with any of the following functions on a port: service loopback, RRPP, Smart Link, and BPDU tunneling for STP. • The spanning tree configurations made in system vi ew take effect globally. Configurations made in L a y e r 2 E t h e r n e t i n t e r f a c e vi e w t a k e e f f e c t o n t h e current interface only. Configurations made in port group view take effect on all member ports in the port group. Configurations made in Layer 2 aggregate interface view take effect only on the aggregate interface. Configurations made on an aggregation member port can take effect only after the port is removed from the aggregation group. • After you enable a spanning tree protocol on a La yer 2 aggregate interface, the system performs spanning tree calculation on the Layer 2 aggregate interface but not on the aggregation member ports. The spanning tree protocol enable state and forwarding state of each selected member port is consistent with those of the corresponding Layer 2 aggregate interface. • Though the member ports of an aggregation group do not participate in spanning tree calculation, the ports still reserve their spanning tree configurations for participating in spanning tree calculation after leaving the aggregation group. STP configuration task list
74 Task Remarks Configuring the root bridge Setting the spanning tree mode Required Configure the device to operate in STP-compatible mode. Configuring the root bridge or a secondary root bridge Optional Configuring the device priority Optional Configuring the network diameter of a switched network Optional Configuring spanning tree timers Optional Configuring the timeout factor Optional Configuring the maximum port rate Optional Configuring the mode a port uses to recognize/send MSTP packets Optional Enabling outputting port state transition information Optional Enabling the spanning tree feature Required Configuring the leaf nodes Setting the spanning tree mode Required Configure the device to operate in STP-compatible mode. Configuring the device priority Optional Configuring the timeout factor Optional Configuring the maximum port rate Optional Configuring path costs of ports Optional Configuring the port priority Optional Configuring the mode a port uses to recognize/send MSTP packets Optional Enabling outputting port state transition information Optional Enabling the spanning tree feature Required Configuring TC snooping Optional Configuring protection functions Optional RSTP configuration task list Task Remarks Configuring the root bridge Setting the spanning tree mode Required Configure the device to operate in RSTP mode. Configuring the root bridge or a secondary root bridge Optional Configuring the device priority Optional Configuring the network diameter of a switched network Optional
75 Task Remarks Configuring spanning tree timers Optional Configuring the timeout factor Optional Configuring the maximum port rate Optional Configuring edge ports Optional Configuring the port link type Optional Configuring the mode a port uses to recognize/send MSTP packets Optional Enabling outputting port state transition information Optional Enabling the spanning tree feature Required Configuring the leaf nodes Setting the spanning tree mode Required Configure the device to operate in RSTP mode. Configuring the device priority Optional Configuring the timeout factor Optional Configuring the maximum port rate Optional Configuring edge ports Optional Configuring path costs of ports Optional Configuring the port priority Optional Configuring the port link type Optional Configuring the mode a port uses to recognize/send MSTP packets Optional Enabling outputting port state transition information Optional Enabling the spanning tree feature Required Performing mCheck Optional Configuring TC snooping Optional Configuring protection functions Optional PVST configuration task list Task Remarks Configuring the root bridge Setting the spanning tree mode Required Configure the device to operate in PVST mode. Configuring the root bridge or a secondary root bridge Optional Configuring the device priority Optional Configuring the network diameter of a switched network Optional
76 Task Remarks Configuring spanning tree timers Optional Configuring the timeout factor Optional Configuring the maximum port rate Optional Configuring edge ports Optional Configuring the port link type Optional Enabling outputting port state transition information Optional Enabling the spanning tree feature Required Configuring the leaf nodes Setting the spanning tree mode Required Configure the device to operate in PVST mode. Configuring the device priority Optional Configuring the timeout factor Optional Configuring the maximum port rate Optional Configuring edge ports Optional Configuring path costs of ports Optional Configuring the port priority Optional Configuring the port link type Optional Enabling outputting port state transition information Optional Enabling the spanning tree feature Required Performing mCheck Optional Configuring protection functions Optional MSTP configuration task list Task Remarks Configuri ng the root bridge Setting the spanning tree mode Optional By default, the device operates in MSTP mode. Configuring an MST region Required Configuring the root bridge or a secondary root bridge Optional Configuring the device priority Optional Configuring the maximum hops of an MST region Optional Configuring the network diameter of a switched network Optional Configuring spanning tree timers Optional Configuring the timeout factor Optional
77 Task Remarks Configuring the maximum port rate Optional Configuring edge ports Optional Configuring the port link type Optional Configuring the mode a port uses to recognize/send MSTP packets Optional Enabling outputting port state transition information Optional Enabling the spanning tree feature Required Configuri ng the leaf nodes Setting the spanning tree mode Optional By default, the device operates in MSTP mode. Configuring an MST region Required Configuring the device priority Optional Configuring the timeout factor Optional Configuring the maximum port rate Optional Configuring edge ports Optional Configuring path costs of ports Optional Configuring the port priority Optional Configuring the port link type Optional Configuring the mode a port uses to recognize/send MSTP packets Optional Enabling outputting port state transition information Optional Enabling the spanning tree feature Required Performing mCheck Optional Configuring Digest Snooping Optional Configuring No Agreement Check Optional Configuring protection functions Optional Setting the spanning tree mode The spanning tree modes include: • STP-compatible mode —The device sends STP BPDUs through all ports. • RSTP mode —The device sends RSTP BPDUs through all ports, and ports that connect to STP devices automatically transitions to the STP-compatible mode. • MSTP mode —The device sends MSTP BPDUs through all ports, and ports that connect to STP devices automatically transitions to the STP-compatible mode. • PVST mode— The device sends PVST BPDUs through all ports and maintains a spanning tree for each VLAN. The number of VLANs that PVST can maintain instances for depends on the switch model. Suppose the number is n, which is 128 on the 5500 EI Switch Series and 32 on the 5500 SI Switch Series. When you configure PVST on devices of different models in a network, to avoid network failures, make sure that the number of VLANs for which PVST maintains instances does not exceed the lowest n.
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The MSTP mode is compatible with the RSTP mode, and the RSTP mode is compatible with the STP mode.
The PVST modes compatibility with the other spanning tree mode varies by port type:
• On an access port, the PVST mode is compatible with any other spanning tree mode in any VLAN.
• On a trunk or hybrid port, the PVST mode is compat ible with any other spanning tree mode in only
VLAN 1.
Whether you need to specify the MSTI or VLAN for the spanning tree configuration varies with the
spanning tree modes.
• In STP-compatible or RSTP mode, do not specify any MSTI or VLAN. Otherwise, the spanning tree
configuration is ineffective.
• In MSTP mode, if you specify an MSTI, the spanning tree configuration is effective for the specified
MSTI. If you specify a VLAN list, the spanning tree configuration is ineffective. If you do not specify
any MSTI or VLAN, the spanning tree configuration is effective for the CIST.
• In PVST mode, if you specify a VLAN list, the spanning tree configuration is effective for the
specified VLANs. If you do not specify any VLAN, the spanning tree configuration is ineffective.
To set the spanning tree mode:
Step Command Remarks
1. Enter system view.
system-view N/A
2. Set the spanning tree mode.
stp mode { stp | rstp | mstp | pvst } MSTP mode by default.
Configuring an MST region
Tw o o r m o r e s p a n n i n g t r e e d e v i c e s b e l o n g t o t h e s a m e M ST r e g i o n o n l y i f t h e y a r e c o n f i g u r e d t o h a v e t h e
same format selector (0 by default, not configurable) , MST region name, MST region revision level, and
the same VLAN-to-instance mapping entries in the MST region, and they are connected via a physical
link.
Configuration restrictions and guidelines
• The configuration of MST region–related paramet ers, especially the VLAN-to-instance mapping
table, will result in a new spanning tree calculation. To reduce the possibility of topology instability,
the MST region configuration takes effect only after you activate it by using the active
region-configuration command, or enable a spanning tree protocol by using the stp enable
command in the case that the spanning tree protocol is disabled.
• The device in PVST mode automatically maps VLANs to MSTIs, and supports more MSTIs than in
MSTP mode. When you change the spanning tree mode from PVST to MSTP, exceeding
VLAN-to-instance mappings (arranged in ascendin g order of MSTI IDs) are silently deleted and
cannot be recovered even if you change the spanni ng tree mode back. To prevent loss of mappings,
do not manually configure VLAN-to-instance mappings in PVST mode.
Configuration procedure
To configure an MST region:
Step Command Remarks
1. Enter system view.
system-view N/A
79
Step Command Remarks
2. Enter MST region view.
stp region-configuration N/A
3. Configure the MST
region name. region-name
name Optional.
The MST region name is the MAC address
by default.
4. Configure the
VLAN-to-instance
mapping table. • instance instance-id vlan
vlan-list
• vlan-mapping modulo
modulo Optional.
Use either command.
All VLANs in an MST region are mapped
to the CIST (or MSTI 0) by default.
5. Configure the MSTP
revision level of the MST
region. revision-level
level Optional.
0 by default.
6. Display the MST region
configurations that are
not activated yet. check region-configuration
Optional.
7. Activate MST region
configuration manually. active region-configuration
N/A
8. Display the activated
configuration
information of the MST
region. display stp region-configuration
[ | { begin | exclude | include }
regular-expression ] Optional.
Available in any view
Configuring the root bridge or a secondary root
bridge
You can have MSTP determine the root bridge of a spanning tree through MSTP calculation, or you can
specify the current device as the root bridge or as a secondary root bridge using the commands that the
system provides.
A device has independent roles in different spanning trees. It can act as the root bridge in one spanning
tree and as a secondary root bridge in another. However, one device cannot be the root bridge and a
secondary root bridge in the same spanning tree.
A spanning tree can have one root bridge only. If two or more devices are designated as the root bridge
in a spanning tree at the same time, the device with the lowest MAC address wins.
When the root bridge of an instance fails or is shut down, the secondary root bridge (if you have
specified one) can take over the role of the primary root bridge. However, if you specify a new primary
root bridge for the instance then, the one you specify, not the secondary root bridge will become the root
bridge. If you have specified multiple secondary root bridges for an instance, when the root bridge fails,
the secondary root bridge with the lowest MAC address is selected as the new root bridge.
Configuration restrictions and guidelines
• You can specify one root bridge for each spanning tree, regardless of the device priority settings.
Once you specify a device as the root bridge or a secondary root bridge, you cannot change its
priority.