On 14 December 2015 at 17:38, Alexey Eromenko <al4321@xxxxxxxxx> wrote: Hey, > * Slow-down of Core Routers. Citation needed. I believe checksum and CRC are linerate and pretty much free in terms of pincount, transistor and thermal. > Any advantages ? > * prevents single mis-routed packets, or a bad option from getting through. Prevents packet mangling, if done right. If there is L3 CRC (not checksum, it's too weak) which excludes changing data (hop count) and specification mandates that it's not recalculated on egress, but ingress value is reused. Then it will guarantee that router or switch does not mangle the data. > Quick result: besides ATM, everybody else seems to cover both headers > and all data. Arbitrarily strong guarantee at L2 does not guarantee integrity at L3. Routers and switches (not fibres/copper!) mangle data and calculate correct L2 CRC on the broken data. I've unfortunately seen[0] this several times in real networks and I know other[1] networks who've seen it as well . I got lucky and was using IPv4, which made the error visible in egress LER's, had I been running IPv6 only, I would have never known that I'm mangling some packets. [0] http://mailman.nanog.org/pipermail/nanog/2014-January/063654.html https://www.ietf.org/mail-archive/web/tsvwg/current/msg12457.html [1] http://www.evanjones.ca/tcp-and-ethernet-checksums-fail.html -- ++ytti