On Thu 7/30/09 6:51 PM, "Lars Eggert" <[email protected]> wrote:
> 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 >>>> regardless of the 4 combinations of packet types (v4-in-v4, v6-in- >>>> v6, >>>> v6-in-v4, or v4-or-v6) being forwarded by LISP routers. >>> >>> 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%. > > 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. It's not about performance; a large percentage of the currently-deployed hardware can¹t do UDP checksum calculations during encapsulation because it doesn¹t have access to the entire packet. Most hardware is streamlined to only provide the first n bytes of a packet to the forwarding engine, where typically n < 128. -J > > Lars > > > _______________________________________________ > lisp mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/lisp -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
