netdev - Re: [PATCH net-next 12/14] gtp: Configuration for zero UDP checksum

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Message-ID: <20170921015522.sv5netrlcj5vebys@nataraja>
Date:   Thu, 21 Sep 2017 09:55:22 +0800
From:   Harald Welte <laforge@...monks.org>
To:     Tom Herbert <tom@...bertland.com>
Cc:     David Miller <davem@...emloft.net>,
        Tom Herbert <tom@...ntonium.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Rohit Seth <rohit@...ntonium.net>
Subject: Re: [PATCH net-next 12/14] gtp: Configuration for zero UDP checksum

Hi Tom,

On Wed, Sep 20, 2017 at 11:09:29AM -0700, Tom Herbert wrote:
> On Mon, Sep 18, 2017 at 9:24 PM, David Miller <davem@...emloft.net> wrote:
> > From: Tom Herbert <tom@...ntonium.net>
> >> Add configuration to control use of zero checksums on transmit for both
> >> IPv4 and IPv6, and control over accepting zero IPv6 checksums on
> >> receive.
> >
> > I thought we were trying to move away from this special case of allowing
> > zero UDP checksums with tunnels, especially for ipv6.
> 
> I don't have a strong preference either way. I like consistency with
> VXLAN and foo/UDP, but I guess it's not required. Interestingly, since
> GTP only carries IP, IPv6 zero checksums are actually safer here than
> VXLAN or GRE/UDP.

Just for the record: I don't care either way and I defer to the kernel
networking developers to decide if they want to have zero UDP checksum
in GTP or not.

The 3GPP specs don't say anything about UDP checksums.  So there's no
requirement to use them, and hence operation without UDP checksums
should be compliant.  Cisco GTP implementation has udp checksumming
configurable, so other implementations also seem to provide both ways.

In general, I would argue one wants UDP checksumming of GTP in all
setups, as while the inner IP packet might be protected, the GTP header
itself is not, and that's what contains important data suhc as the TEID
(Tunnel Endpoint ID).  But that's of course just my personal opinion,
and I'm not saying we should prevent people from using lower protection
if that's what they want.

-- 
- Harald Welte <laforge@...monks.org>           http://laforge.gnumonks.org/
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