Re: [PATCH net-next 12/14] gtp: Configuration for zero UDP checksum
From: Tom Herbert <hidden>
Date: 2017-09-21 22:41:04
On Wed, Sep 20, 2017 at 6:55 PM, Harald Welte [off-list ref] wrote:
Hi Tom, On Wed, Sep 20, 2017 at 11:09:29AM -0700, Tom Herbert wrote:quoted
On Mon, Sep 18, 2017 at 9:24 PM, David Miller [off-list ref] wrote:quoted
From: Tom Herbert <redacted>quoted
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.
The tradeoffs and requirements of zero UDP6 checksums are discussed at length in RFC6935 and RFC6936. Given other implementations make it configurable it should also be here. Tom
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