Understanding and Troubleshooting the Autostate Feature in Catalyst Switches

Introduction

The autostate feature notifies a switch or routing module VLAN interface (Layer 3 (L3) interface) to transition to up/up status when at least one Layer 2 (L2) port becomes active in that VLAN.

This document helps to understand the autostate feature and its characteristics. After configuring the interface <vlan-id> command on routers, the interface stays in the up/down or down/down status, depending on the platform. This document discusses why this happens, and how the L3 and L2 interfaces interact with each other in the control plane after being activated.

Before You Begin

Conventions

For more information on document conventions, see the Cisco Technical Tips Conventions.

Prerequisites

There are no specific prerequisites for this document.

Components Used

This document is not restricted to specific software and hardware versions.

The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.

Understanding Autostate

Autostate is implemented on CatOS and IOS Cisco based switches by default. On some CatOS platforms, this feature can be disabled in order to allow redundancy in special scenarios. On IOS based switches, this feature cannot be disabled.

The router VLAN interfaces have to fulfill the following general conditions to be up/up:

• VLAN exists and is in active status on the switch VLAN database.

• VLAN interface exists on the router and is not administratively down.

• At least one L2 (access port or trunk) port exists and has a link up on this VLAN. The latest implementation of the autostate feature allows synchronization to Spanning-Tree Protocol (STP) port status.

  A VLAN interface will be brought up after the L2 port has had time to converge (that is, transition from listening-learning to forwarding). This will prevent routing protocols and other features from using the VLAN interface as if it were fully operational. This also prevents other problems, such as routing black holes, from occurring.

• At least one L2 (access port or trunk) port is in spanning-tree forwarding state on the VLAN.

Autostate Configuration on Catalyst Switches

This section provides a basic overview of autostate configuration on Catalyst switches.

Catalyst 6000 Native IOS / Catalyst 4000 Cisco IOS (Supervisor III and IV) / Catalyst 3550

For these switches, the autostate feature is enabled by default. The autostate feature is synchronized with the STP state.

The protocol line state for the VLAN interfaces will come up when the first switchport belonging to the corresponding VLAN link comes up and is in spanning-tree forwarding state.

Issue the following commands to check the status of all conditions during troubleshooting:

• sh vlan

• sh int vlan <vlan-id>

• sh int <fast | gig> mod/port (L2 port)

• sh int <fast | gig> mod/port trunk (if L2 port is trunk)

• sh spanning-tree vlan <vlan-id>

Note: Autostate synchronized with STP was introduced in code 12.1(8a)E and later. Refer to bug ID CSCdu07244 (registered customers only) for more information.

Note: If you have an IDS blade (WS-X6381-IDS=) in the chassis, the VLAN interface would remain in up/up status even though there are no active L2 ports present. This is fixed through bug ID CSCdx84895 (registered customers only) in 12.1.13E and later releases. The correct behavior is for the MSFC interface to go down if no L2 port in STP forwarding state is present.

Catalyst 6000 Hybrid Running CatOS with MSFC card (SUP IA, SUP II, MSFC, MSFC 2)

For these switches, the following additional conditions must be fulfilled, in addition to the up/up status general conditions:

• The router (Multilayer Switch Feature Card (MSFC)) port (15/1,16/1) must be in trunking mode.

• The VLAN must be allowed on the trunk to the MSFC.

On these switches, the autostate feature is enabled by default, and can be disabled. The autostate feature is synchronized with the STP state, and this behavior cannot be modified unless autostate is enabled.

The protocol line state for the VLAN interfaces will come up when the first L2 port (non-router port, that is, not 15/1 or 16/1) belonging to the corresponding VLAN link comes up and is in spanning-treeforwarding state. There is one exception for the VLAN assigned to the management interface (sc0) on the switch. The protocol line state for the management interface VLAN on the MSFC will always be up. The sc0 should always be up after the switch boots. This interface, however, can be forced to administratively down.

Issue the following commands to check the status of all conditions during troubleshooting:

• On MSFC, issue the show int vlan <vlan-id> command.

• On the switch, issue the sh vlan , sh port mod/port (L2 port), sh trunk mod/port (if the L2 port is a trunk), and sh spantree <vlan-id> commands.

Disable the Autostate Feature

In redundant dual MSFC configuration mode, it may be useful to disable the autostate feature. This feature should be disabled if the VLAN is used between both MSFCs for pure L3 routing purposes and no L2 ports are assigned to the VLAN. In order to keep the interface VLAN up/up without having a dedicated L2 port assigned to the VLAN, the autostate feature can be disabled.

Issue the following command for the current autostate feature setting:

Switch (enable) sh msfcautostate     
MSFC Auto port state: enabled

Issue the following command to disable the autostate feature:

  
Switch (enable) set msfcautostate disable 
Switch (enable) sh msfcautostate          
MSFC Auto port state: disabled
Switch (enable)

Note: Autostate synchronized with STP for Catalyst hybrid switches is supported starting with 5.5(10) and 6.3(1) . Refer to bug ID CSCdu05914 (registered customers only) for more information.

Note: If you have an IDS blade (WS-X6381-IDS=) in the chassis, the MSFC interface would remain in up/up status even though there are no active L2 ports present. This is fixed through bug ID CSCdt75094 (registered customers only) in 6.2.2 , 6.3.1 and later releases. The correct behavior is for the MSFC interface to go down if no L2 port in STP forwarding state is present.

Catalyst 5000 with RSM/RSFC Card

For these switches, the following additional conditions must be fulfilled, in addition to the up/up general conditions:

• The router (Route Switch Module (RSM) / Route Switch Feature Card (RSFC) ) port must be in trunking mode.

• The VLAN must be allowed on the router trunk.

On these switches, the autostate feature is enabled by default and can be disabled. The autostate feature is not synchronized with the STP state.

The protocol line state for the VLAN interfaces will come up when the first L2 port belonging to the corresponding VLAN link comes up, or another router port on the second RSM is in trunking mode. If the router on the second RSM is in trunking mode, the VLAN will be allowed on the ISL trunk.

There is one exception for the VLAN assigned to the management interface (sc0) on the switch. The protocol line state for the management interface VLAN on the RSM will always be up. The sc0 should always be up after the switch boots. This interface, however, can be forced to administratively down.

Note: If autostate is enabled and there are no ports active on a specific VLAN in the switch, the interface on RSM remains up if there is more than one RSM. This allows traffic to flow between the two RSMs on that VLAN without disabling the autostate feature. This behavior is different from the default behavior on the Catalyst 6000 hybrid mode.

Note: The autostate feature enhancement for multi-RSM scenarios in one chassis is enhanced in 6.1.2. (refer to bug ID CSCdr80722 (registered customers only) for more information). Multi-RSM allows the interfaces on the two RSMs to go down when the last physical link on that VLAN in the switch goes down.

Issue the following commands to check the status of all conditions during troubleshooting:

• On the RSM, issue the show int <vlan-id> command.

• On the switch, issue the sh vlan, sh port mod/port (L2 port), sh trunk mod/port (if the L2 port is a trunk), and sh spantree <vlan-id> commands.

Issue the following command to view the current autostate feature setting:

Switch (enable) sh rsmautostate 
RSM Auto port state: enabled
Multi-RSM Option: enabled

Issue the following command to disable the autostate feature:

Switch (enable) set rsmautostate disable 
RSM port auto state disabled.
Switch (enable) sh rsmautostate          
RSM Auto port state: disabled
Multi-RSM Option: enabled
Switch (enable)

Issue the following command to disable the multi-RSM feature in autostate:

Switch (enable) sh rsmautostate            
RSM Auto port state: enabled
Multi-RSM Option: enabled
Switch (enable) set rsmautosta multirsm disable 
RSM port auto state multiple RSM disabled.
Switch (enable) sh rsmautostate                 
RSM Auto port state: enabled
Multi-RSM Option: disabled
Switch (enable)

Note: Disabling multi-RSM is an additional feature of autostate. To use this feature, autostate must be enabled.

Catalyst 4000 (Supervisor I and II) with Layer 3 Modules

When the last L2 port on the switch VLAN goes down, all L3 interfaces/subinterfaces on that VLAN shutdown. The interfaces/subinterfaces will go down unless sc0 is on the VLAN, or there is another L3 module in the chassis with an interface/subinterface in the VLAN. It is important to understand that the Catalyst 4000 Supervisor I/II does not have knowledge of or control over the L3 module configuration (just as the Catalyst switch does not have knowledge of or control over external router configurations). Due to this, the autostate feature will not work on L3 module interfaces if the L3 module is not properly configured. Refer to the following guidelines:

• The autostate feature is enabled by default. Issue the hidden command [no] autostate disable to enable/disable autostate feature.

• The autostate feature is not synchronized with the STP state.

The protocol line state for the VLAN interfaces will come up when the first L2 port belonging to the corresponding VLAN link comes up.

Issue the following command to see what Catalyst 4000 L3 services module interfaces have been shut down or brought up by the autostate feature:

Router#sh autostate entries 
Autostate Feature is currently enabled on the system.

Issue the following command to disable the autostate feature (this is a hidden command):

Router#autostate disable
Disabling Autostate
Router#sh autostate entries 
Autostate Feature is currently disabled on the system.

Issue the following command to re-enable the autostate feature:

Router#no autostate disable 
Enabling Autostate
Router#sh autostate entries 
Autostate Feature is currently enabled on the system.

Troubleshooting the Autostate Feature on IOS Based Switches

Perform these troubleshooting steps if the VLAN interface is down.

1. This is the symptom of a VLAN interface being in up/down status.

   Corgon-6000#sh int vlan 151
   Vlan151 is up, line protocol is down
   
    !--- Line protocol on interface VLAN 151 is down. !--- You need to investigate why this line protocol is not up !--- (at least one L2 port exists, and there should be a !--- link up on this VLAN). 
   
   

2. Check to make sure that VLAN 151 exists in the VLAN database and is active. The command below shows that the VLAN exists and is active on the switch.

    
   Corgon-6000#sh vlan 151 | i 151
   151  VLAN151                          active    Gi4/10
   151  enet  100151     1500  -      -      -        -    -        0      0   
   Corgon-6000#
   
    !--- VLAN 151 exists in VLAN database and is active. !--- L2 port Gig4/10 is assigned to VLAN 151. 
   
   

3. Check the status of interface gig 4/10 assigned to VLAN 151.

   Corgon-6000#sh int gig 4/10
   GigabitEthernet4/10 is up, line protocol is down (notconnect)
   
   Corgon-6000#sh run int gig 4/10 
   Building configuration...
   Current configuration : 182 bytes
   !
   interface GigabitEthernet4/10
    no ip address
    logging event link-status
    logging event bundle-status
    switchport
    switchport access vlan 151
    switchport mode access
   end
   

4. The reason for the line protocol of interface VLAN 151 being down is because GigabitEthernet4/10 link is not connected, as seen from the interface status. It is possible that no device is connected to the interface or that the link has cabling or auto-negotiation issues preventing the link from being up.

5. Connect the device to GigabitEthernet4/10 to bring the interface link up.

    
   Mar 11 12:10:52.340: %LINK-3-UPDOWN: Interface GigabitEthernet4/10,changed state to up
   Mar 11 12:10:53.156: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet4/10,changed state to up
   Corgon-6000#
   Corgon-6000#
   Corgon-6000#sh int vlan 151
   Vlan151 is up, line protocol is down 
   

6. Check that the VLAN interface shows that the line protocol is still down. You need to investigate why this line protocol is not up. Make sure that at least one L2 port is in spanning-tree forwarding state on this VLAN.

    
   Corgon-6000#sh spanning-tree vlan 151
   VLAN0151
     Spanning tree enabled protocol rstp
     Root ID    Priority    32768
                Address     00d0.003f.8897
                This bridge is the root
                Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
     Bridge ID  Priority    32768
                Address     00d0.003f.8897
                Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
                Aging Time 300
   
   Interface        Role Sts Cost      Prio.Nbr Type
   ---------------- ---- --- --------- -------- --------------------------------
   Gi4/10           Desg LRN 4         128.202  P2p 
   Corgon-6000#
   

7. The Spanning-tree port status is LRN, which means learning state. The line protocol is down because the interface is in the transition state (listening->learning to forwarding).

   Corgon-6000#
   Mar 11 12:11:23.406: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan151, 
      changed state to up

   Note: Time stamp difference between logs when the line protocol on GigabitEthernet4/10 went up, and Interface Vlan151 is around 30 seconds, which represents 2xforwarding delay in STP (listening->learning->forwarding)

   Corgon-6000#sh int vlan 151
   Vlan151 is up, line protocol is up
   

8. The line protocol is up. You need to verify spanning-tree port status on the L2 port (should be forwarding).

   Corgon-6000#sh spanning-tree vlan 151
   VLAN0151
     Spanning tree enabled protocol rstp
     Root ID    Priority    32768
                Address     00d0.003f.8897
                This bridge is the root
                Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
     Bridge ID  Priority    32768
                Address     00d0.003f.8897
                Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
                Aging Time 300
   
   
   Interface        Role Sts Cost      Prio.Nbr Type
   ---------------- ---- --- --------- -------- --------------------------------
   Gi4/10           Desg FWD 4         128.202  P2p 
   
    !--- Verified spanning-tree port status on L2 port !--- is FWN = forwarding.
    
   

Troubleshooting the Autostate Feature on CatOS Based Switches

Perform these troubleshooting steps if the VLAN interface is down.

1. This is the symptom of a VLAN interface on the MSFC being down/down

   Topvar-msfc>sh int vlan 151
   Vlan151 is down, line protocol is down 
   
    !--- Line protocol is down (not administratively down). If so, issue the !--- no shutdown command under the interface. !--- Line protocol on interface VLAN 151 is down in this output. !--- You need to investigate why this line protocol is not up !--- (at least one L2 port exists, and there should be a !--- link up on this VLAN).
   
   

2. Check to make sure that VLAN 151 exists in the VLAN database and is active. The command below shows that the VLAN exists and is active on the switch.

   Topvar (enable) sh vlan 151      
   VLAN Name                             Status    IfIndex Mod/Ports, Vlans
   ---- -------------------------------- --------- ------- ------------------------
   151  VLAN151                          active    284         3/1     15/1  
   

3. As you can see, L2 ports 3/1 and 15/1(MSFC) are assigned to VLAN 151. Check the status of port 3/1 assigned to VLAN 15. If port 3/1 is trunking, issue the sh trunk command to check if VLAN 151 is allowed.

   Topvar (enable) sh port 3/1   
   Port  Name                 Status     Vlan       Duplex Speed Type
   ----- -------------------- ---------- ---------- ------ ----- ------------
    3/1                      disabled      151        auto     auto    10/100BaseTX
   
    !--- Since the only port (3/1) is diabled, !--- the line protocol for interface VLAN 151 is down.
   
   

4. Enable port 3/1, as shown below.

   Topvar (enable) set port enable 3/1
   Port 3/1 enabled.
   2003 Mar 12 05:42:10 %PAGP-5-PORTTOSTP:Port 3/1 joined bridge port 3/1
   Topvar (enable) sh port 3/1
   Port     Name                 Status     Vlan     Duplex  Speed  Type
   ----- -------------------- ---------- ---------- ------   -----  ------------
    3/1                       connected    151       a-half  a-10   10/100BaseTX
   

5. Session into the MSFC and verify the status of the VLAN interface again.

   Topvar (enable) ses 15          
   Trying Router-15...
   Connected to Router-15.
   Escape character is '^]'.
   
   Topvar-msfc>sh int vlan 151
   Vlan151 is down, line protocol is down 

6. As you can see, the line protocol on interface VLAN 151 is still down. You need to investigate why this line protocol is not up. At least one L2 port is in spanning-tree forwarding state on this VLAN. Make sure by checking the switch, as shown below.

   Topvar (enable) sh spantree 151
   VLAN 151
   Spanning tree mode          PVST+ 
   Spanning tree type          ieee
   Spanning tree enabled
   Designated Root             00-07-4f-1c-e8-47
   Designated Root Priority    0
   Designated Root Cost        119
   Designated Root Port        3/1                     
   Root Max Age   20 sec   Hello Time 2  sec   Forward Delay 15 sec
   Bridge ID MAC ADDR          00-05-00-a9-f4-96
   Bridge ID Priority          32768
   Bridge Max Age 20 sec   Hello Time 2  sec   Forward Delay 15 sec
   Port                     Vlan Port-State    Cost      Prio Portfast Channel_id
   ---------------------- ---- ------------- --------- ---- -------- ----------
    3/1                       151  listening       100        32   disabled 0         
   
   Topvar (enable)

7. Spanning-tree port status is in listening yet. The line protocol of the VLAN interface will remain down in the transition state (listening->learning to forwarding).

   Topvar (enable) sh spantree 151
   VLAN 151
   Spanning tree mode          PVST+ 
   Spanning tree type          ieee
   Spanning tree enabled
   Designated Root             00-07-4f-1c-e8-47
   Designated Root Priority    0
   Designated Root Cost        119
   Designated Root Port        3/1                     
   Root Max Age   20 sec   Hello Time 2  sec   Forward Delay 15 sec
   Bridge ID MAC ADDR          00-05-00-a9-f4-96
   Bridge ID Priority          32768
   Bridge Max Age 20 sec   Hello Time 2  sec   Forward Delay 15 sec
    
   
   Port                     Vlan Port-State    Cost      Prio Portfast Channel_id
   ------------------------ ---- ------------- --------- ---- -------- ----------
    3/1                     151  forwarding          100   32 disabled 0         
   15/1                    151  forwarding            4   32 enabled  0         
   
   Topvar (enable)

8. Spanning-tree port status on the L2 port is forwarding. The line protocol on the interface VLAN should now be up. Verify that the line protocol is up, as shown below:

   Topvar (enable) ses 15
   Trying Router-15...
   Connected to Router-15.
   Escape character is '^]'.
   
   Topvar-msfc>sh int vlan 151
   Vlan151 is up, line protocol is up
   It is up in up/up status as expected.
   

9. If there is still problem with the interface VLAN being up/up, check that the router port is in trunking mode, and that the VLAN is allowed on the router trunk. A sample output is shown below.

   Topvar (enable) sh trunk 15/1
   * - indicates vtp domain mismatch
   Port      Mode            Encapsulation    Status        Native vlan
   --------  -----------      -------------    ------------    -----------
   15/1      nonegotiate      isl                   trunking   1
   
    
   Port      Vlans allowed on trunk
   --------  ---------------------------------------------------------------------
   15/1      1-1005,1025-4094
    
   
   Port      Vlans allowed and active in management domain 
   --------  ---------------------------------------------------------------------
   15/1      1,151
   
   Port      Vlans in spanning tree forwarding state and not pruned
   --------  ---------------------------------------------------------------------
   15/1      1,151
   
   Topvar (enable)
   
    !--- VLAN 151 is allowed, and is in spanning-tree !--- forwarding state. VLAN 151 is not pruned.
   
   

Related Information

• set msfcautostate
• set rsmautostate
• Understanding and Configuring Spanning-Tree Protocol (STP) on Catalyst Switches
• Technical Support & Documentation - Cisco Systems