[Olsr-users] Question on multiple interfaces

[Henning Rogge]

I would say OLSR knows because it knows the incoming (local)
interface. Of course seeing the same neighbor link on two interfaces
is a bit unusual so I am not sure it will work well with our
implementation.

But it does work well with our OLSRd v2 implementation.

Henning Rogge

On Thu, Aug 1, 2013 at 12:56 PM, Thijs van Veen <(spam-protected)> wrote:
> Hello,
>
> I have a small question (based on the RFC
> http://tools.ietf.org/html/rfc3626) regarding multiple interface nodes.
>
> Given the following network with node A having 3 interfaces, 2 of which
> are connected to B (single interface) and the other connected to C. B
> and C are connected and all links are symmetric.
>
> +----------------+
> |       A         |
> |  if.0 if.1 if.2 |
> +----------------+
>    \   /     /
>      B -- C
>
> Paths from A to B are:
> A.if.0 -> B
> A.if.1 -> B
> A.if.2 -> C -> B
>
> When considering the link A <-> B, will OLSR distinguish between the
> links if.0 <-> B and if.1 <-> B?
>
> To me the RFC suggests it only considers the faster link (judging from
> HELLO processing on A):
>
> From the RFC 3.4. Packet Processing and Message Flooding:
> "3.1  if there exists a tuple in the duplicate set, where:
>
>                              D_addr    == Originator Address, AND
>
>                              D_seq_num == Message Sequence Number
>
>                then the message has already been completely processed
>                and MUST not be processed again.
> "
> So only the first link is considered, because while received on
> different interfaces, both messages have the same originator address and
> sequence number causing the latter to be ignored;
>
> Or, if the message is not ignored.
>
> From the RFC, 7.1. Populating the Link Set:
> "1    Upon receiving a HELLO message, if there exists no link tuple
>           with
>
>                L_neighbor_iface_addr == Source Address
>
>           a new tuple is created with
>
>                L_neighbor_iface_addr = Source Address
>
>                L_local_iface_addr    = Address of the interface
>                                        which received the
>                                        HELLO message
>
>                L_SYM_time            = current time - 1 (expired)
>
>                L_time                = current time + validity time
>
> 2   The tuple (existing or new) with:
>
>                L_neighbor_iface_addr == Source Address
>
>           is then modified as follows:
>
>           2.1  L_ASYM_time = current time + validity time;
>
>           2.2  if the node finds the address of the interface which
>                received the HELLO message among the addresses listed in
>                the link message then the tuple is modified as follows:
>
>            2.2.1
>                     if Link Type is equal to LOST_LINK then
>
>                          L_SYM_time = current time - 1 (i.e., expired)
>
>           2.2.2
>                     else if Link Type is equal to SYM_LINK or ASYM_LINK
>                     then
>
>                          L_SYM_time = current time + validity time,
>
>                          L_time     = L_SYM_time + NEIGHB_HOLD_TIME
>
>           2.3  L_time = max(L_time, L_ASYM_time)
> [...]
> "
> Only the first link is considered and for longer, because the latter
> message (sent from same interface) has not been ignored and modifies the
> time-outs of the first. This would cause the slower interface to be
> added in the event the first interface had already been removed, but
> this only reverses the problem.
>
> The other way around (processing on B), would work because the message
> got sent from different interfaces.
>
> --
>   Thijs van Veen
>   (spam-protected)
>
> --
> http://www.fastmail.fm - One of many happy users:
>   http://www.fastmail.fm/help/overview_quotes.html
>
>
> --
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> (spam-protected)
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