[Babel-users] Next Hop TLV meaning

[Lorenzo Ghiro]

Thank you so much,

so if I understand correctly, when A sends an Update to B, B needs to know
address of A and, according to the proper circumstances, B gets address of
A either from IPv6 packet's source address (case 1) or from The Next-hop
TLV sent on purpose by A (case 2).

Considering the following scenario

  x         y   z        w
A  -------  B  -------  C

with B that has, in its routing table, an entry for prefix of C with
next-hop set to w.
I would like that by announcing this route, B includes the fact that its
selected next-hop is w.
So that receiving an "enriched" Update from B for <Prefix of C, NH=w>, a
neighbor node is able to check if it is the selected next-hop
(e.g. A will fail, because x==w->false, while C will succeed w==w->true).
If I understand correctly what I would call my "next-hop" TLV has a
different meaning from the RFC one, therefore I should put the info I need
into a subtlv right?

Thank you and best regards

Lorenzo



2016-12-06 17:43 GMT+01:00 Juliusz Chroboczek <jch at irif.fr>:

> > 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
>
>
>
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