This article outlines the reason behind the generation of log message:

This message has no effect on service and can be safely ignored. A procedure to avoid displaying it is provided.

The default IPV6 link local address starts in the range of FE80:. However, if this default value is changed on the router to another address, perhaps starting with FE81, the router will start generating the following error message /kernel: nd6_cache_lladdr: no route to src fe80::ad19:d69b:851e:32f9 dst=ff02::0002 received on ifl.

These logs will appear only when there is another IPV6 host connected to the other end of the interface on the router. Consider a scenario where a PC with IPV6 addressing enabled is connected to a router. On the router, the default link local address is changed to fe81::ad19:d69b:851e:32f9. The PC will have a default link local address starting with FE80. As soon as the PC comes online, it starts sending a Router Solicitation message with a source link-local address in the range of FE80::/64. Upon receipt of this RS from an unknown source link-local address, the router generates the subject log message. In this case, the address starting with FE80 is unknown to the router and it responds with the log message.

These messages are display notices only and can be safely ignored. They do not have any service impact. To avoid displaying them, enable the following command on the device:

set protocols neighbor-discovery onlink-subnet-only

• Understanding IPv6