Re: [lisp] IPv6 UDP checksum issue

[Lars Eggert]

Hi,

could you share some data on how much of a performance impact we're
talking about here? I was under the (maybe naive) impression that
checksum offloading was practically ubiquitous these days.

One of the problems with IPv6 is that is so similar to IPv4 but
different enough to cause pain for implementations. So since we can
use 0 UDP checksums for IPv4 in UDP in IPv4, we would want to build
(or use existing hardware) that does IPv6-or-IPv4 in UDP in IPv6.

if the existing hardware sends UDP packets over IPv6 with checksum zero, it is not compliant to the RFCs. If you're building new hardware, you will have to sacrifice some gates to do a UDP checksum calculation. Alternatively, you could pick a different encapsulation or change the IETF consensus on using UDP in IPv6.

Sorry, but we want to build practical products. If you don't build
practical standards, vendors will violate them.

Let me be blunt: If you are going to ignore IETF consensus, why are you here? If you want to change that consensus, please convince the IETF to do so. Ignoring the consensus and the process by which we arrive at it is not an option.

There are no practical reasons to use outer header UDP checksums

v6-in-v4, or v4-or-v6) being forwarded by LISP routers.

regardless of the 4 combinations of packet types (v4-in-v4, v6-in- v6,

I hear you, but is there any quantifiable downside to just compute
the checksums, esp. if it can be done in hardware?

A hardware forwarding engine is not going to compute a pseudo-header
checksum and compute every byte of a packet. It's just not going to
happen.

I freely admit I'm not a hardware guy, but a hardware checksum was cheaply doable at (then) high-performance in 1995. See RFC1936.

There has never been a requirement to do this before. My guess is you
can slow performance by 20%.

Lars

There hasn't been a requirement for IPv4 because there is an IP header checksum. As to the performance numbers, my guess would be different, which is why I asked if you had data.

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