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hamnarauf committed Jul 10, 2023
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Expand Up @@ -82,9 +82,9 @@ Multiple Spanning Tree Protocol (MSTP) enhances the Spanning Tree Protocol (STP)
# Introduction
Spanning Tree Protocol (STP) prevents bridge looping on LANs that include redundant links. Per VLAN Spanning Tree (PVST) is a modification of STP that allows for running separate instances of spanning tree for each VLAN.

Multiple Spanning Tree Protocol (MSTP) allows frames assigned to different VLANs to follow separate paths. These paths are based on independent Multiple Spanning Tree Instances (MSTI), within Multiple Spanning Tree (MST) Region. These Regions and the other Bridges and LANs are connected into a single Common Spanning Tree (CST).
Multiple Spanning Tree Protocol (MSTP) allows the mapping of multiple VLANs to a single instance hence allows frames assigned to different VLANs to follow separate paths. These paths are based on independent Multiple Spanning Tree Instances (MSTI) that run inside MST Region. VLANs that are not explicitly assigned to any specific MSTI are automatically managed by the default Internal Spanning Tree (IST) associated with instance 0. MSTP ensures that frames with a given VID are assigned to only one of the MSTIs or the IST within the Region and the assignment is consistent amongst all the Bridges within the region.

MSTP connects all Bridges and LANs with a single Common and Internal Spanning Tree (CIST). The connectivity calculated for the CIST provides the CST for interconnecting these Regions, and an Internal Spanning Tree (IST) within each Region. MSTP ensures that frames with a given VID are assigned to one and only one of the MSTIs or the IST within the Region, that the assignment is consistent amongst all the Bridges within the region.
To facilitate the interconnection among MST regions, a Common Spanning Tree (CST) is established, allowing communication between switches in different MST regions. MSTP connects all Bridges and LANs with a single Common and Internal Spanning Tree (CIST). CIST refers to the combination of the Common Spanning Tree (CST) and the Internal Spanning Tree (IST) and it is the overall spanning tree instance that spans the entire MSTP domain.

By providing VLAN-to-instance mapping, MSTP ensures that a limited number of instances are created, allowing for network segregation. In contrast, PVST lacks control over VLAN-to-instance mapping, leading to numerous instances and inefficient memory utilization.

Expand All @@ -93,21 +93,24 @@ STP only supports a single instance, resulting in under utilized network bandwid
MSTP calculates spanning trees on the basis of Multiple Spanning Tree Bridge Protocol Data Units (MST BPDUs).

<div align="center">
MSTP BPDU Format<br>
<img src="images/MSTP_BPDU.png" alt="MSTP BPDU">
<p>MSTP BPDU Format</p>
</div><br>
<div align="center">
MSTI Configuration Messages<br>
<img src="images/MSTI_config_message.PNG" alt="MSTP Config Message">
<p>MSTI Configuration Messages</p>
</div>

*Refer to [RFC IEEE 802.1s-2002](https://standards.ieee.org/ieee/802.1s/1042/) for MSTP BPDU details.*

# Requirements
1. Support the assignment of multiple VLAN(s) to multiple spanning tree identifiers (MSTI) within each region.
1. Support the creation of Multiple Spanning Tree Instances (MSTIs).
1. Support the assignment of one or more VLANs to a specific MSTI within a region.
1. Support the option to assign a region name and revision number to MSTP regions in order to achieve unique identification of VLAN to instance mapping across switches.
1. Support path selection and forwarding behaviour in MSTI to optimize network performance within each instance by configuring a distinct root bridge.
1. Support the configuration of spanning tree parameters such as forward delay, hello timer, hop count, max age.
1. Support the configuration of spanning tree parameters such as forward delay, hello timer, hop count and max age.
1. The Destination Mac Address will be 01:80:C2:00:00:00 for MSTP BPDUs.
1. Support compatibility with networks employing different spanning tree protocols, such as STP, RSTP via Protocol Migration.
1. Support compatibility with networks employing different spanning tree protocols, such as STP, RSTP and PVST via Protocol Migration.

# Architecture Design
Following diagram explains the architectural design and linkages for MSTP. MSTP uses multiple existing SONiC containers, configuration details of each is mentioned below as well.
Expand All @@ -126,7 +129,9 @@ Responsible for all MST protocol related calculations. BPDUs are sent and receiv
### STPSync
A process running as a part of STPD. Responsible for updating all the MSTP states in APP DB.

The BPDU rx/tx, handling of changes related to port or LAG using netlink events and STP port state sync to Linux Kernel will function the same as PVST.
The BPDU rx/tx, BPDU processing, handling of timers, handling of changes related to port or LAG using netlink events and STP port state sync to Linux Kernel will function the same as PVST.

*Refer to [PVST's STP Container Details](https://github.com/sandeep-kulambi/SONiC/blob/631ab18211e7e396b138ace561b7a04e7f7b49a1/doc/stp/SONiC_PVST_HLD.md#34-stp-container)*

## SWSS Container

Expand Down Expand Up @@ -160,8 +165,8 @@ Following existing table of CONFIG_DB will be modified for MSTP implementation:
#### STP_GLOBAL_TABLE
A new value of `mstp` for `mode` column and a new column for holding `max-hops`
```
mode = "pvst" / "mstp" / "none" ; a new option for mstp (DEF: "none")
max_hops = 1*3DIGIT ; max hops (1 to 255, DEF: 20)
mode = "pvst" / "mstp" / "disable" ; a new option for mstp (DEF: "disable")
max_hops = 1*3DIGIT ; max hops (1 to 255, DEF: 20)
```
Other fields of this table i.e rootguard_timeout, forward_delay, hello_time, max_age, priority will also be used to hold the configurations received from CLI.

Expand Down Expand Up @@ -211,11 +216,9 @@ region_name = 1*32CHAR ; region name (DEF: mac-address of sw
revision = 1*5DIGIT ; region revision (0 to 65535, DEF: 0)
bridge_id = 16HEX ; bridge id
cist_root_bridge_id = 16HEX ; CIST root’s bridge id
regional_root_bridge_id = 16HEX ; Regional root’s bridge id
external_path_cost = 1*9DIGIT ; path cost to CIST bridge
internal_path_cost = 1*9DIGIT ; path cost to regional root bridge
root_port = ifName ; Root port name
root_max_age = 1*2DIGIT ; Max age as per CIST root bridge
external_path_cost = 1*9DIGIT ; path cost to CIST root bridge
root_port = ifName ; root port name
root_max_age = 1*2DIGIT ; max age as per CIST root bridge
root_hello_time = 1*2DIGIT ; hello time as per CIST root bridge
root_forward_delay = 1*2DIGIT ; forward delay as per CIST root bridge
root_max_hops = 1*3DIGIT ; max hops as per CIST root bridge
Expand All @@ -224,7 +227,7 @@ hello_time = 1*2DIGIT ; hello time in secs (1 to 10, DEF
forward_delay = 1*2DIGIT ; forward delay in secs (4 to 30, DEF: 15)
max_hops = 1*3DIGIT ; max hops (1 to 255; DEF:20)
last_topology_change = 1*10DIGIT ; time in secs since last topology change occured
topology_change_count = 1*10DIGIT ; Number of times topology change occured
topology_change_count = 1*10DIGIT ; number of times topology change occured
instances_configured = 1*2DIGIT ; total number of instances configured (DEF: 1)
```

Expand All @@ -235,11 +238,11 @@ key = MSTP_INSTANCE:"Instance"instanceid ; instance id
vlanids = vlan_id-or-range[,vlan_id-or-range] ; list of VLAN IDs
oper_status = "active" / "inactive" ; instance is active in mstp
bridge_id = 16HEXDIG ; bridge id
msti_root_bridge_id = 16HEXDIG ; MSTI regional root’s bridge id
msti_root_path_cost = 1*9DIGIT ; port path cost to MSTI root
msti_root_port = ifName ; Root port name
regional_root_bridge_id = 16HEXDIG ; regional root’s bridge id
internal_root_path_cost = 1*9DIGIT ; port path cost to regional root
root_port = ifName ; root port name
last_topology_change = 1*10DIGIT ; time in sec since last topology change occured
topology_change_count = 1*10DIGIT ; Number of times topology change occured
topology_change_count = 1*10DIGIT ; number of times topology change occured
```

#### MSTP_INSTANCE_PORT_TABLE
Expand All @@ -249,7 +252,8 @@ key = MSTP_INSTANCE_PORT:"Instance"instanceid:ifname ; instan
port_num = 1*3DIGIT ; port number of bridge port
path_cost = 1*9DIGIT ; port path cost (1 to 200000000)
priority = 1*3DIGIT ; port priority (0 to 240, DEF:128)
port_state = "state" ; STP state-disabled, block, listen, learn, forward
port_state = "state" ; STP state - disabled, block, listen, learn, forward
port_role = "role" ; STP port role - root, designated, blocking, alternate, master
desig_root = 16HEXDIG ; designated root
desig_cost = 1*9DIGIT ; designated cost
desig_bridge = 16HEXDIG ; designated bridge
Expand Down Expand Up @@ -319,7 +323,7 @@ MSTP design requires one new attribute `SAI_HOSTIF_TRAP_TYPE_MSTP` for control t
## Del VLAN from instance
![MSTP VLAN Del](images/MSTP_vlan_del.png)

Update port-state, topology change and instance-interface events remain the same as depicted in sequence diagrams of PVST.
Update port-state, topology change and instance-interface events remain the same as depicted in [Sequence Diagrams of PVST](https://github.com/sandeep-kulambi/SONiC/blob/631ab18211e7e396b138ace561b7a04e7f7b49a1/doc/stp/SONiC_PVST_HLD.md#4-flow-diagrams).

# Configuration Commands
Following configuration commands will be provided for configuration of MSTP:
Expand Down Expand Up @@ -370,9 +374,9 @@ Following commands are used for spanning-tree configurations on per instance, pe
- cost-value: Range: 1-200000000

## Show Commands
- show spanning_tree region brief
- show spanning_tree instance \<instance-id\>
- show spanning_tree instance interface \<instance-id\> \<ifname\>
- show spanning_tree

The output of this command will be as follows for `mstp`:
```
Spanning-tree Mode: MSTP
Expand All @@ -382,8 +386,6 @@ Revision : 0
CIST Bridge Identifier : 32768002438eefbc3
CIST Root Identifier : 32768002438eefbc3
CIST External Path Cost : 0
CIST Regional Root Identifier : 32768002438eefbc3
CIST Internal Path Cost : 0
Instances configured : 1
Last Topology Change : 0s
Number of Topology Changes : 0
Expand All @@ -393,19 +395,53 @@ CIST Root Timers : MaxAge 20s Hello 2s FwdDly 15s MaxHops 20
MSTP instance 0 - VLANs 10, 20, 30
-------------------------------------------------------------------------------------------------
Bridge MSTI Root Bridge RootPath Root Port LastTopology Topology
Bridge Regional Bridge RootPath RootPort LastTopology Topology
Identifier Identifier Cost Identifier Change Change
hex hex sec cnt
32768002438eefbc3 32768002438eefbc3 0 128.13 0 0
MSTP Port Parameters:
Port Prio Path Port Uplink State Designated Designated Designated
Num rity Cost Fast Fast Cost Root Bridge
Ethernet13 128 4 Y N FORWARDING 0 32768002438eefbc3 32768002438eefbc3
Port Prio Path Port Uplink State Role Designated Designated Designated
Num rity Cost Fast Fast Cost Root Bridge
Ethernet13 128 4 Y N FORWARDING Root 0 32768002438eefbc3 32768002438eefbc3
```
- show spanning_tree region

```
Region Name : regionA
Revision : 0
CIST Bridge Identifier : 32768002438eefbc3
CIST Root Identifier : 32768002438eefbc3
CIST External Path Cost : 0
Instances configured : 1
Last Topology Change : 0s
Number of Topology Changes : 0
Bridge Timers : MaxAge 20s Hello 2s FwdDly 15s MaxHops 20
CIST Root Timers : MaxAge 20s Hello 2s FwdDly 15s MaxHops 20
```

- show spanning_tree instance \<instance-id\>

```
MSTP instance 0 - VLANs 10, 20, 30
-------------------------------------------------------------------------------------------------
Bridge Regional Bridge RootPath RootPort LastTopology Topology
Identifier Identifier Cost Identifier Change Change
hex hex sec cnt
32768002438eefbc3 32768002438eefbc3 0 128.13 0 0
```

- show spanning_tree instance interface \<instance-id\> \<ifname\>

```
Port Prio Path Port Uplink State Role Designated Designated Designated
Num rity Cost Fast Fast Cost Root Bridge
Ethernet13 128 4 Y N FORWARDING Root 0 32768002438eefbc3 32768002438eefbc3
```

- show spanning_tree statistics region
### Statistics Commands
- show spanning_tree statistics instance \<instance-id\>
```
MSTP instance 0 - VLANs 10, 20, 30
Expand All @@ -416,7 +452,6 @@ PortChannel15 20 6 4 1
```

## Clear Commands
- sonic-clear spanning_tree statistics region
- sonic-clear spanning_tree statistics instance \<instance-id\>
- sonic-clear spanning_tree statistics instance interface \<instance-id\> \<ifname\>

Expand All @@ -433,7 +468,7 @@ Following debug commands will be supported for displaying internal data structur
- debug spanning_tree dump instance interface \<instance-id\> \<ifname\>

## Disabled Commands
Following commands are used to configure parameters at VLAN level and these commands are disabled if spanning-tree mode is MSTP:
Following commands are used to configure parameters at VLAN level and these commands are disabled if spanning-tree mode is `mstp`:

- config spanning_tree vlan (enable|disable) \<vlan\>
- config spanning_tree vlan forward_delay \<vlan\> \<fwd-delay-value\>
Expand All @@ -443,7 +478,7 @@ Following commands are used to configure parameters at VLAN level and these comm
- config spanning_tree vlan interface cost \<vlan\> \<ifname\> \<value\>
- config spanning_tree vlan interface priority \<vlan\> \<ifname\> \<value\>

Also, Instance level commands will be disabled if spanning-tree mode is PVST.
Also, Region level and Instance level commands will be disabled if spanning-tree mode is `pvst`.


# YANG Model
Expand Down Expand Up @@ -492,9 +527,9 @@ module sonic-stp {
type enumeration {
enum "pvst";
enum "mstp";
enum "none";
enum "disable";
}
default "none";
default "disable";
description "STP mode";
}
Expand Down

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