Subject: Re: [PATCH net-next v2 07/12] gtp: use ephemeral source port

From: Harald Welte <[email-masked]>
Date: Sat, 12 Dec 2020 11:07:05 +0100

Hi Jonas,

On Fri, Dec 11, 2020 at 01:26:07PM +0100, Jonas Bonn wrote:
> From 3GPP TS 29.281:
> "...the UDP Source Port or the Flow Label field... should be set dynamically
> by the sending GTP-U entity to help balancing the load in the transport
> network."

You unfortuantely didn't specifiy which 3GPP release you are referring to.

At least in V15.7.0 (2020-01)  Release 15 I can only find:

"For the messages described below, the UDP Source Port (except as
specified for the Echo Response message) may be allocated either
statically or dynamically by the sending GTP-U entity.  NOTE: Dynamic
allocation of the UDP source port can help balancing the load in the
network, depending on network deployments and network node
implementations."

For GTPv0, TS 29.060 states:

"The UDP Source Port is a locally allocated port number at the sending
GSN/RNC."

unfortuantely it doesn't say if it's a locally allocated number globally
for that entire GSN/RNC, or it's dynamic per flow or per packet.

As I'm aware of a lot of very tight packet filtering between GSNs,
I would probably not go for fully dynamic source port allocation
without some kind of way how the user (GTP-control instance) being
able to decide on that policy.

-- 
- Harald Welte <[email-masked]>           http://laforge.gnumonks.org/
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