One of the reasons that IPv6 (rfc2460) dropped the header checksum
that was in IPv4 is that with link layers all doing FCS it served no
purpose. For the same reason TCP and UDP checksums server no purpose.
The link layer checksum fails and the packet is dropped. Since this
is usually not at the last hop (often a local Ethernet) but instead in
a WAN link, the packet never arrives at the destination for anything
to count IP header or TCP or UDP checksum errors.
Also all of the following handle both data integrity and congestion
avoidance the same way:
UDP over IP over Ethernet
UDP over IP over MPLS over Ethernet
UDP over IP over MPLS over UDP over IP over Ethernet
s/Ethernet/{POS,GFP,etc}/ for all of the above
s/^UDP over IP/PW/ for all of the above
In all of the above cases data integrity is handled by the link layer.
In all of the above cases congestion avoidance is handled by the
application (or not at all). Whether MPLS is carried directly over a
link layer or over UDP/IP over a link layer makes no difference.
Curtis
In message <290E20B455C66743BE178C5C84F1240847E63346BF@xxxxxxxxxxxxxxxxxxxxxx>
l.wood@xxxxxxxxxxxx writes:
> Really, you'd want to expose the pseudoheader check at endhosts; a well-instrumented Linux box could tell you a lot
> about checksum failures.
>
> But in this case, a router would be decapping UDP/MPLS tunnels as an endpoint, so could report on checksum failures -
> if the checksum wasn't zero.
>
> Lloyd Wood
> http://about.me/lloydwood
> ________________________________________
> From: Dino Farinacci [farinacci@xxxxxxxxx]
> Sent: 12 January 2014 21:37
> To: Wood L Dr (Electronic Eng)
> Cc: <mark.tinka@xxxxxxxxx>; <mpls@xxxxxxxx>; gorry@xxxxxxxxxxxxxx; lisp@xxxxxxxx; david.black@xxxxxxx; randy@xxxxxxx; tsvwg@xxxxxxxx; jnc@xxxxxxx; ietf@xxxxxxxx
> Subject: Re: [lisp] [mpls] draft-ietf-mpls-in-udp was RE: gre-in-udp draft (was: RE: [tsvwg] Milestones changed for tsvwg WG)
>
> > Do any routers count TCP/UDP checksum failures, much less
> > expose the count via SNMP?
>
> Typically they do but only for packets destined to them. Much like hosts would check the header checksum.
>
> Dino
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