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The RFC for Neighbor Discovery (RFC4861), in section 8 states:

"A router MUST be able to determine the link-local address for each of its neighboring routers in order to ensure that the target address in a Redirect message identifies the neighbor router by its link-local address. For static routing, this requirement implies that the next- hop router's address should be specified using the link-local address of the router. For dynamic routing, this requirement implies that all IPv6 routing protocols must somehow exchange the link-local addresses of neighboring routers."

Yet, all documentation I encountered, including Cisco and Juniper, use simple Global Unicast Address or Local Unicast Address as next hop for IPv6 static routing.

. is the use of link-local address mandatory as IPv6 static routing next hop?

. is the use of link-local address a best practice as IPv6 static routing next hop?

Thanks for any clarification

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In practice using GUA addresses is perfectly fine.

The restriction (well, strong recommendation, as it is specified as SHOULD) is to make it possible for the device with the static route to send redirect messages. These days redirect messages are often already disabled because of security and performance issues, so using a GUA as next hop is no problem.

  • So if I understand well, we have a RFC on one side; and security, performances, ease of use (using FE80::/10 as next hop is less straightforward) and common practices on the other. Should we formulate the answer as 'As a rule of thumb, don't use link-local address as next hop'? What would be the cases where using a link-local address should be preferred ? Saving /64 subnets in core routing ? – networkIT May 7 '18 at 19:28
  • Routing protocols use link local next hops. It's great for automatic stuff! When manually configuring a route, using global addresses makes things easier for the network admin. – Sander Steffann May 8 '18 at 7:12

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