14 Jul
2017
14 Jul
'17
12:54 a.m.
Hi Harald and Jeo,
Thank you for the code review. They are really helpful!
On 7/13/17, 11:14 AM, "Joe Stringer"
<joe(a)ovn.org> wrote:
On 13 July 2017 at 00:12, Harald Welte <laforge(a)gnumonks.org> wrote:
The flow listed out here is an example for the nature of the match
that can be performed, but the actual match rule that is programmed
by the control plane should wildcard the tun_src as noted by Harald.
It is the control plane’s responsibility to enforce the 3GPP Specifications,
e.g. creating flow rules to make TEID the only criteria for matching an
encapsulated packet to the tunnel.
I will provide a 3GPP compliant example in the next version, thank Harald
for pointing it out.
-Jiannan
I'm not familiar with the details here, but
does this imply that you
are matching on the outer (transport layer) source IP address? If so,
please note this is in violation of the 3GPP specifications for GTP,
which require explicitly that the TEID is the *only* criteria for
matching an encapsulated packet to the tunnel. Basically anyone can
send you an encapsulated packet from any random source IP, just as long
as the TEID matches a tunnel, it will be decapsulated.
This is [presumably] in order to take care of mobility, as the
subscribers' phone moves around different MME/S-GW/SGSN, each having
different source IP addresses.
I think that this will be hard to avoid; the several existing tunnel
implementations that OVS plugs into all allow matching on the outer
addresses/ports, I don't see a good way to restrict it without
introducing completely new metadata_dst paths for GTP. I'd prefer not
to introduce something like this if we can avoid it; several tunnels
currently share all of the same metadata_dst code and that's proven
sufficient for all cases so far. If someone wishes to implement the
3GPP standard correctly then they should not create matches like this.
In quite a few cases, OVS tends to take the approach that we give the
user the tools to do what they need to do, but if they wish to shoot
themselves in the foot then that's up to them. We can of course work
towards ensuring the OVS userspace guides users in the right direction
though.