[Babel-users] Next Hop TLV meaning

[Juliusz Chroboczek]

> I do not understand the meaning of "next-hop" TLV for a subsequent Update.
[...]
> What should I do put the route's next-hop into update messages?

1. For an IPv6 route, do not send a Next Hop TLV.  In its absence, the
   receiver will derive the next hop address from the IPv6 packet's source
   address.

       α     β
     A ------- B

   Node A has IPv6 address α.  It sends an Update to B in an IPv6 address
   with source address α.  B uses α as the route's next hop.

2. For an IPv4 route, precede the Update with a Next Hop TLV with the
   on-link address of the sending node.  The receiver will use this
   address as the route's next-hop.

       α     β
     A ------- B
       ℵ    ℶ

   Node A has IPv6 address α and IPv4 address ℵ (that's "aleph").  It
   sends an IPv4 Update to B, with source address α.  Since the route
   requires an IPv4 next hop, B needs to learn ℵ somehow — so it consults
   the preceding Next Hop packet, which contains ℵ.

— Juliusz