The link-up delay timer during an ISL failure

Configure the link-up delay timer and exclude LAGs so that if an ISL goes down, the downed ISL does not impact the state of the VLAN, and its SVI that is not a part of a VSX LAG. This SVI is part of at least one orphan port (besides the ISL LAG which is not a VSX LAG).

The following scenario explains what happens:

  • During the ISL going down (before the initial synchronization): As long as the secondary VSX node has a port that is a member of a VSX LAG, the associated SVI of the VLAN (transported by the VSX LAG) turns to OFF/SHUT on the VSX secondary node. This situation occurs regardless of orphan ports carrying the given VLAN.

  • During the running of the link-up delay timer (after the initial synchronization):

    As long as the secondary VSX node has a port that is a member of a VSX LAG, the associated SVI of the VLAN (transported by the VSX LAG) turns to OFF/SHUT on the VSX secondary node. This situation occurs regardless of orphan ports carrying the given VLAN.

    The associated SVI of the VLAN transported by VSX LAG restores to ON/UP on the VSX secondary node, only if the following two conditions are met:

    • The VSX LAG is excluded from the link-up delay timer by the following command: linkup-delay-timer exclude lag-list

    • The given VLAN is not allowed on a VSX LAG that is not in the part of the exclusion set.

The following example shows how a network was configured so an SVI that was not part of a VSX LAG (SVI 16 in this case) was restored. This example also shows the link-up delay timer and the exclusion of LAGs.

The network in the following example was configured as:

  • VLAN 16 is set on 1/1/5 (access).

  • VLAN 10 tagged as VSX LAG 11. *

  • LAG 1 is not a VSX LAG.*

  • LAG 2 and LAG 11 are VSX LAGs.

*This information is not accessible from the following example. 

switch# show vlan 10

--------------------------------------------------------------------------------------------------------------
VLAN  Name                              Status  Reason                Type      Interfaces
--------------------------------------------------------------------------------------------------------------
10    test_vlan10                       up      ok                    static    1/1/7,lag1-lag2,lag11-lag12,
                                                                                lag14,lag16,lag112
switch# show vlan 15

--------------------------------------------------------------------------------------------------------------
VLAN  Name                              Status  Reason                Type      Interfaces
--------------------------------------------------------------------------------------------------------------
15    ZTP_VLAN                          up      ok                    static    lag1-lag2

switch# show vlan 16

--------------------------------------------------------------------------------------------------------------
VLAN  Name                              Status  Reason                Type      Interfaces
--------------------------------------------------------------------------------------------------------------
16    VLAN16                            up      ok                    static    1/1/5,lag1

switch# show vlan 200

--------------------------------------------------------------------------------------------------------------
VLAN  Name                              Status  Reason                Type      Interfaces
--------------------------------------------------------------------------------------------------------------
200   interco_vlan                      up      ok                    static    lag1-lag2

switch# show run vsx
vsx
    system-mac 00:00:00:01:01:01
    inter-switch-link lag 1
    role secondary
    keepalive peer 192.168.10.1 source 192.168.10.2 vrf KeepAlive
    linkup-delay-timer exclude lag 2
    linkup-delay-timer 60


switch# show vsx status linkup-delay
Configured linkup delay-timer                                : 60 seconds
Initial sync status                                          : Completed
Delay timer status                                           : Running
Linkup Delay time left                                       : 0 minutes 58 seconds
Interfaces that will be brought up after delay timer expires : lag11-lag12,lag14,lag16,lag112
Interfaces that are excluded from delay timer                : lag2


switch# show int vlan10

Interface vlan10 is down
 Admin state is up
 Description:
 Hardware: Ethernet, MAC Address: 94:f1:28:1d:ad:00
 IPv4 address 10.10.10.3/26
 active gateway 10.10.10.1 00:00:00:00:11:01
 active gateway 2002:0a0a:0a00::1 00:00:00:00:66:01
switch# sh int vlan15

Interface vlan15 is up
 Admin state is up
 Description:
 Hardware: Ethernet, MAC Address: 94:f1:28:1d:ad:00
 IPv4 address 10.10.15.12/24
switch# sh int vlan16

Interface vlan16 is up
 Admin state is up
 Description:
 Hardware: Ethernet, MAC Address: 94:f1:28:1d:ad:00
 IPv4 address 10.10.16.2/24
switch# sh int vlan200

Interface vlan200 is up
 Admin state is up
 Description:
 Hardware: Ethernet, MAC Address: 94:f1:28:1d:ad:00
 IPv4 address 10.10.212.6/29

As expected, SVI 10 is in pseudo-shut during the link-up delay. SVI 10 was a part of LAG 2 which is in exclusion. SVI 16 is up, as expected because SVI 16 was not part of a VSX LAG.