[dpdk-users] [dpdk-dev] IPV4/IPV6 TCP/UDP Pseudo Header Checksum APIs

Hyong Youb Kim hyonkim at cisco.com
Wed Nov 28 16:07:19 CET 2018


On Tue, Oct 23, 2018 at 11:01:58AM +0200, Olivier Matz wrote:
> Hi,
> 
> You are right, the current code does not take IP or IPv6 options
> in account. I think this should be considered as a bug.
> 
> The fix for IPv4 is not complicated, I did a quick draft here:
> http://git.droids-corp.org/?p=dpdk.git;a=commitdiff;h=96a6978ef6814e1450e1bd65fbce91c3d85b3121
> 
> For IPv6, it is more complex than expected:
> https://tools.ietf.org/html/rfc2460.html#section-8.1
> 
> - we need to skip extension headers
> - we need to parse routing headers and use the proper destination
>   address in the pseudo header checksum
> 
> This makes me think that the API is not adequate. Asking the user
> to provide the headers in a contiguous memory without specifying
> the length is quite dangerous, especially if the header comes from
> outside, as it can trigger out of bound accesses.
> 
> I wonder if we shouldn't switch to a mbuf based API instead, and
> deprecate the old one.
> 
> Thoughts?
> Olivier
> 

I have been looking into a similar issue because
rte_net_intel_cksum_prepare(), which is used by most tx_pkt_prepare
handlers, does not work when ipv6 extensions are present. That
function is using rte_ipv6_phdr_cksum(). And this makes
rte_eth_tx_prepare() kinda useless for any workloads that encounter
ipv6 extensions.

There are 2 routing header types now (2 and 3).

https://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtml#ipv6-parameters-3

In addition to these routing headers, there is also ipv6
mobility. Pseudo header's source address is supposed to be the address
in the Home Address option.

https://tools.ietf.org/html/rfc6275#page-36

Who knows there may be future extensions that affect pseudo
header.. We can probably make rte_ipv6_phdr_cksum() to understand all
existing headers that affect pseudo header, but it will still not be future
proof. Should at least document the limitations for rte_ipv6_phdr_cksum()..

-Hyong


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