Troubleshooting vIST Failure

About this task

When you use Virtual Inter-Switch Trunk (vIST), all critical network traffic runs on this link. If vIST fails, network protocols such as RIP, VRRP, OSPF, and VLACP go down and eventually cause a network outage.

vIST uses an SPBM tunnel to virtually connect two nodes that can be anywhere in the SPBM cloud. Even if the two vIST nodes are directly connected by an MLT link, the vIST VLAN does not have MLT ports as members. Instead, it is configured to be an SPBM C-VLAN.

Note

Note

For more information on vIST and a configuration example, see MultiLink Trunking and Split MultiLink Trunking.

The vIST tunnel is up as long as there is SPBM connectivity between the IST peers. If there is a vIST failure, check the following procedure for some possible reasons:

Procedure

  1. Enter Global Configuration mode:

    enable

    configure terminal

  2. Verify that the vIST VLAN is configured on the vIST switch:

    show virtual-ist

  3. Verify that an I-SID is associated with the vIST VLAN:

    show isis spbm i-sid discover

    Important

    Important

    The I-SID associated with the vIST VLAN should be the same on the vIST peer, and this I-SID should not be used anywhere else in the network.

  4. Verify that the vIST peers are on the same subnet.
  5. If peer ARP is not resolved, enable trace level 14 to see if ARP request/response are being sent/received.
  6. If vIST is not up, check the mac fdb table and verify that the peer MAC is synchronized:

    show vlan mac-address-entry <1-4059>

  7. If the vIST peer MAC is learned, check to see if the peer IP address is reachable.
    1. Use show virtual-ist to obtain the vIST peer IP address.
    2. Ping the peer IP address.
  8. If unable to ping the peer IP address, check to see if ARP is resolved.

    show ip arp vlan <vid>

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