A group of links may contain upstream links and downstream links. When all upstream links in a group are down, Link State Tracking (LST) shuts all the downstream links down. In order to let the peer on the other side know that it needs to stop sending traffic on the downstream links. When the upstream link recovers, LST brings up the downstream links, letting the peers know that they may resume forwarding traffic on those links.

A link can be a member of several groups. A downstream interface is shut down if at least one of the groups requests a shutdown and is brought back up if all groups request it to be up.

In situations with only downstream links in a group (no upstream links), the downstream links will stay up.

Configuring Link State Tracking

The following is a basic example of how to configure link state tracking group and tracking VLAN.

To configure Link State Tracking group:

Create tracking group. Run:

switch-1 (config) # link state tracking group group1

Configure link type on the interface. Run:

switch-1 (config) # interface ethernet 1/2 link type upstream
switch-1 (config) # interface ethernet 1/1 link type downstream

Add interfaces into the group. Run:

switch-1 (config) # interface ethernet 1/1 link state tracking group group1
switch-1 (config) # interface ethernet 1/2 link state tracking group group1

To configure Link State Tracking VLAN:

Create VLAN. Run:
```
switch-2 (config) # vlan 100
```

Configure VLAN members. Run:

switch-2 (config) # interface ethernet 1/1 switchport access vlan 100
switch-2 (config) # interface ethernet 1/2 switchport access vlan 100

Configure link type on the interface. Run:

switch-2 (config) # interface ethernet 1/2 link type upstream
switch-2 (config) # interface ethernet 1/1 link type downstream

Create link state tracking VLAN. Run:

switch-2 (config) # link state tracking vlan 100

To verify Link State Tracking configuration, run:

switch-1 (config) # show link state tracking group group1

---------------------------------------------------------------------------------------
Group              Port Type      Interface          Admin Status   Operational Status
--------------------------------------------------------------------------------------- 
group1             Upstream       Eth1/2             Enabled        Up

Link State Tracking Commands

link type

	link type {downstream \| upstream} no link type Configures an interface’s link direction. The no form of the command deletes the interface’s link direction configuration.
Syntax Description	downstream	Configures interface as downstream
	upstream	Configures interface as upstream
Default	N/A
Configuration Mode	config interface ethernet
History	3.7.1000
Example	switch (config interface ethernet 1/1)# link type downstream
Related Commands	show link state tracking
Notes	IPL, loopback, and VLAN interfaces are not supported. An interface can be either upstream or downstream but not both.

link state tracking group

	link state tracking group <group-name> no link state tracking group <group-name> Creates a link state tracking group if one does not exist, and if applied to a specific interface, then it adds that interface to the group. The no form of the command deletes a link state tracking group, and if applied to a specific interface, then it removes that interface from the group.
Syntax Description	group-name	Name for link state tracking group
Default	N/A
Configuration Mode	config config interface ethernet config interface port-channel config interface mlag-port-channel
History	3.7.1000
Example	switch (config interface ethernet 1/1)# link state tracking group group1
Related Commands	show link state tracking
Notes	The maximum number of tracking groups/VLANs is 64 Link state tracking group name should not contain any of the following characters: [*/\"\\ ;,.?<>:@#$%^&()=] and should consist of no more than 255 characters Tracking the link state of member ports in a LAG or MLAG is not supported

link state tracking vlan

	link state tracking vlan <vlan-id> no link state tracking vlan <vlan-id> Creates a VLAN link state tracking group. All VLAN members are automatically added into this group. The no form of the command deletes a VLAN link state tracking group.
Syntax Description	vlan-id	ID of VLAN whose link state to track
Default	N/A
Configuration Mode	config
History	3.7.1000
Example	switch (config)# link state tracking vlan 100
Related Commands	show link state tracking
Notes	The maximum number of tracking groups/VLANs is 64

show link state tracking

	show link state tracking [group <group-name> \| vlan <vlan-id>] Displays link state tracking configuration.
Syntax Description	group	Displays link state tracking per tracking group
	vlan	Displays link state tracking per VLAN
Default	N/A
Configuration Mode	Any command mode
History	3.7.1000
Example
switch (config)# show link state tracking --------------------------------------------------------------------------------------- Group Port Type Interface Admin Status Operational Status --------------------------------------------------------------------------------------- Vlan 100 Upstream Eth1/54 Enabled Down Vlan 100 Downstream Eth1/1 Enabled Down (by tracking) Vlan 100 Unassigned Eth1/2 Enabled Up Vlan 101 Upstream Eth1/54 Enabled Down Vlan 101 Downstream Eth1/1 Enabled Down (by tracking) Vlan 101 Unassigned Eth1/2 Enabled Up group1 Downstream Eth1/1 Enabled Down (by tracking)
Related Commands	link type link state tracking group link state tracking vlan
Notes	The maximum number of tracking groups/VLANs is 64

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