Subject: [Int-area] draft-ietf-intarea-gre-ipv6-11 and IPv6 header checksum

From: "Templin, Fred L" <[email-masked]>
Date: Thu, 6 Aug 2015 14:35:13 +0000

Here's an idea for GRE encapsulation in IPv6. When the Checksum Present
bit is 1, the Checksum field contains a Checksum of the GRE header plus
payload as usual, but the Reserved1 field encodes a checksum of the IPv6
encapsulation header. Also treat Checksum value 0 as "no checksum" the
same as for UDP checksums.

Thanks - Fred
[email-masked]

---

From: Tom Herbert <[email-masked]>
Date: Thu, 6 Aug 2015 09:11:50 -0700

> same as for UDP checksums.
Seems like a possibility. The alternate checksum field could provide a
checksum over GRE header plus the typical pseudo header. RFC2784
indicates Reserved1 must be transmitted as zero, but does not indicate
how a non-zero value on receive is handled-- I think we need to assume
that implementations currently ignore a non-zero value. Unfortunately,
RFC2784 didn't include the provision for zero value as "no checksum
present" in Checksum, and allowing this now wouldn't be forward
compatible.

Tom

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