netdev - Re: [PATCH net-next v2 10/12] gtp: add IPv6 support

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Date:   Sat, 12 Dec 2020 14:59:14 +0100
From:   Jonas Bonn <jonas@...rbonn.se>
To:     Harald Welte <laforge@...filter.org>
Cc:     netdev@...r.kernel.org, pablo@...filter.org
Subject: Re: [PATCH net-next v2 10/12] gtp: add IPv6 support

Hi Harald,

On 12/12/2020 12:22, Harald Welte wrote:
> Hi Jonas,
> 
> thanks again for your patches, they are very much appreciated.
> 
> However, I don't think that it is "that easy".
> 
> PDP contexts (at least) in GPRS/EDGE and UMTS come in three flavors:
> * IPv4 only
> * IPv6 only
> * IPv4v6 (i.e. both an IPv4 and an IPv6 address within the same tunnel)
> 
> See for example osmo-ggsn at https://git.osmocom.org/osmo-ggsn
> for an userspace implementation that covers all three cases,
> as well as a related automatic test suite containing cases
> for all three flavors at
> https://git.osmocom.org/osmo-ttcn3-hacks/tree/ggsn_tests
> 
> If I read your patch correctly
> 
> On Fri, Dec 11, 2020 at 01:26:10PM +0100, Jonas Bonn wrote:
>> -	struct in_addr		ms_addr_ip4;
>> -	struct in_addr		peer_addr_ip4;
>> +	struct in6_addr		ms_addr;
>> +	struct in6_addr		peer_addr;
> 
> this simply replaces the (inner) IPv4 "MS addr" with an IPv6 "MS addr".

Yes, that's correct.  It's currently an either-or proposition for the UE 
address.

I actually wanted to proceed a bit carefully here because this patch 
series is already quite large.  I do plan on adding support for multiple 
MS addresses, but already just juggling mixed inner and outer tunnels 
seemed challenging enough to review.

> 
> Sure, it is an improvement over v4-only.  But IMHO any follow-up
> change to introduce v4v6 PDP contexts would require significant changes,
> basically re-introducing the ms_add_ip4 member which you are removing here.

I think we ultimately need to take the MS (UE address) member out of the 
PDP context struct altogether.  A single PDP context can apply to even 
more than two addresses as the UE can/should be provisioned with 
multiple IPv6 addresses (as I understand it, superficially).

> 
> Therefore, I argue very much in favor of intrducing proper IPv6 support
> (including v4v6) in one go.

For provisioning contexts via Netlink, I agree that we should try to 
avoid pathological intermediate steps.  For the actual packet handling 
of outer and inner IPv6 tunnels, I think it's moot whether or not the 
PDP contexts support multiple addresses or not: the subsequent step to 
extend to multiple IP's is a bit of churn, but doesn't immediately seem 
overly intrusive.

Anyway, I'll look into making this change...

Thanks for the review!

/Jonas

> 
> Regards,
> 	Harald
>