how does NDP determine default router with multiple gateways?

[notaciscoguy]

I am attempting to wrap my head around NDP collecting default router information for automatic addresses. this makes perfect sense in a network that only has a single gateway, however I can find no information regarding how a device selects a default router for its IPv6 configuration if there are multiple routers located on the same network segment. 

[Harold Ritter]

Hi,

Please refer to RFC4861, section 6.3.6 for a description of how the default router should be selected.

https://tools.ietf.org/html/rfc4861#section-6.3.6

Furthermore, RFC4191 introduces the configuration of a preference that can be used to select a default router over another.

https://tools.ietf.org/html/rfc4191

Regards,