After configuring LLT over UDP using IPV6, one of the configured link may show DOWN status for lltstat command

Last published : Sep 11, 2026
On configuring LLT over UDP using IPV6, one of the configured links shows down status. However, the IP address for this link can successfully be pinged.
This happens due to the default route settings for ipv6. In case of UDP, the Linux Kernel's UDP APIs rely on the Linux networking stack to send data. In some cases the networking stack uses a different source IP address than the correct one to send packets on a link.
Workaround:
Set the proper static routes so that the networking stack can use the correct network interfaces. Use the following steps to add a static route using the smitty utility:
  1. Run the command: # smitty tcpip
  2. Select IPV6 Configuration from the menu and press Enter.
  3. Select IPV6 Static Routes and then Add an IPV6 Static Route from the menu.
  4. Specify the value for * IPV6 DESTINATION Address,* IPV6 GATEWAY Address , and Network Interface fields to set source and destination address.
Related information
LLT known issues