Some small OSPF changes

[Ondrej Zajicek]

On Fri, Feb 24, 2012 at 11:30:19PM +0400, Alexander V. Chernikov wrote:
> Hello list!
>
> There are several improvements that can be applied to OSPF:
>
> 1) At the moment TTL is not explicitly set in per-interface sockets, so
> multicast messages are sent with default OS ttl (which is 255 on *BSD).

Hmm, you are right, default TTL for multicast seems to be 1 on Linux,
so i missed that.

>    sk->flags = SKF_LADDR_RX;
> +  sk->ttl = 1;

This will break vlinks (they use same sockets). As TTL for unicast can
be different than TTL for multicast, the simplest fix would be to keep
sk->ttl for unicast and add a ttl arg to sk_setup_multicast(). This will
leave 255 TTL for unicast packets on NBMA ifaces, which is probably not
a big issue.

Another possibility is to have a common independent socket
for vlinks, but i am not sure whether vlinks need an iface-specific
socket - have to be checked what are requirements for vlink
sockets. This would be probably better for implementing TTL
security later.



> 2) At the moment bird totally ignores neighbor MTU. We should at least  
> print warning (or error) if neighbor MTU differs. This greatly  
> simplifies debugging procedures.

OK

> +      if ((ps->iface_mtu != ifa->iface->mtu) && ((ifa->type != OSPF_IT_VLINK) ||
> +		((ps->iface_mtu != 0) && (ifa->iface->mtu != 0))))

Isn't ps->iface_mtu still in network order here?



3) Another problem with OSPF sockets is that they depend on device
routes in routing tables and depend on kernel to choose proper source
address (if there are more IPv4 prefixes on one iface.

In Linux, the multicast  source address is specified in IP_MULTICAST_IF or
IP_ADD_MEMBERSHIP, unicast source address is chosen based on dst. address.

I am not sure, but if i remember correctly, this does not work on
(at least some) BSD.

Depending on device routes is not a big problem, but makes it a bit more
fragile (and also a reason why we do not support _real_ unnumbered ptp
ifaces).

Some time ago i tried to use IP_PKTINFO to fix this, works for Linux but
it does not work on some BSD for raw sockets (which are used for OSPF).
I guess that using IP_HDRINCL would work, but it is ugly, just for IPv4
and not clearly encapsulated (reserved buffer space just on IPv4).
Any BSD hints for that?


-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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