netdev - Re: [PATCH net-next 09/14] gtp: Allow configuring GTP interface as standalone

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Date:   Wed, 20 Sep 2017 18:07:49 +0200
From:   Andreas Schultz <aschultz@...p.net>
To:     Tom Herbert <tom@...bertland.com>
Cc:     Tom Herbert <tom@...ntonium.net>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Harald Welte <laforge@...monks.org>,
        Rohit Seth <rohit@...ntonium.net>
Subject: Re: [PATCH net-next 09/14] gtp: Allow configuring GTP interface as
 standalone



On 20/09/17 17:57, Tom Herbert wrote:
> On Wed, Sep 20, 2017 at 8:27 AM, Andreas Schultz <aschultz@...p.net> wrote:
>> On 19/09/17 02:38, Tom Herbert wrote:
>>>
>>> Add new configuration of GTP interfaces that allow specifying a port to
>>> listen on (as opposed to having to get sockets from a userspace control
>>> plane). This allows GTP interfaces to be configured and the data path
>>> tested without requiring a GTP-C daemon.
>>
>>
>> This would imply that you can have multiple independent GTP sockets on the
>> same IP address.That is not permitted by the GTP specifications. 3GPP TS
>> 29.281, section 4.3 states clearly that there is "only" one GTP entity per
>> IP address.A PDP context is defined by the destination IP and the TEID. The
>> destination port is not part of the identity of a PDP context.
>>
> We are in no way trying change GTP, if someone runs this in a real GTP
> network then they need to abide by the specification. However, there
> is nothing inconsistent and it breaks nothing if someone wishes to use
> different port numbers in their own private network for testing or
> development purposes. Every other UDP application that has assigned
> port number allows configurable ports, I don't see that GTP is so
> special that it should be an exception.

GTP isn't special, I just don't like to have testing only features in 
there when the same goal can be reached without having to add extra 
stuff. Adding code that is not going to be useful in real production 
setups (or in this case would even break production setups when enabled 
accidentally) makes the implementation more complex than it needs to be.

You can always add multiple IP's to your test system and have the same 
effect without having to change the ports.

Regards
Andreas

> 
> Tom
>