[Babel-users] Next Hop TLV meaning

[Lorenzo Ghiro]

Hi everybody, once again I need your help! :)
I do not understand the meaning of "next-hop" TLV for a subsequent Update.

I built a very basic network with two Babel nodes connected via a wired
link. Host1 interface's address is 1.1.1.1, Host2 interface's address is
2.2.2.2

Well, consider that after some time host1 installed the route 2.2.2.2/32,
learned via host2, therefore next-hop for that route is 2.2.2.2. Here below
I put the output that I get from a printf* put into flushupdates before
calling really_send_update

host1> Time:661.531458 Sending UpdateC for learned route<Prefix:2.2.2.2/32
> - NH:2.2.2.2 - contribute: 2>


*[when invoking printf, a babel_route *route is available, so I believe I
am not doing wrong in getting the NH as shown in this little piece of code

>   printf("%ld.%06ld\t Sending UpdateC for learned route<Prefix:%s - NH:%s
> - contribute: %i>\n",
>                 now.tv_sec, now.tv_usec,
>                 format_prefix(route->src->prefix, route->src->plen),
>                 format_address(route->nexthop), (1 + total_contribute));

]

At host2 side I expect that, receiving the just sent update, the preceding
NH TLV should carry the address 2.2.2.2, but instead, as you can see I get
1.1.1.1 (actually the source address of this packet)

host2> Time: 661.532299 Received nh 1.1.1.1 (1) from
> fe80::e43d:3ff:feeb:bf58 on h2-eth0.
> host2> Time: 661.532299 Received update for 2.2.2.2/32 from
> fe80::e43d:3ff:feeb:bf58 on h2-eth0.


Although this result complies with the RFC
<<The next-hop address for this update is taken from the last preceding
Next Hop TLV with a matching address family in the same packet; if no
such TLV exists, it is taken from the network-layer source address of
this packet>>
nevertheless I do not understand why it works like this :(

What should I do put the route's next-hop into update messages? I should
put the "route->nexthop" into a subtlv? Or I just need to better understand
the use of  already present next-hop TLV?

Thank you and best regards,

Lorenzo
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.alioth.debian.org/pipermail/babel-users/attachments/20161206/150bb50f/attachment.html>