RFC 6333, "Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion", August 2011Source of RFC: softwire (int)
Errata ID: 5847
Publication Format(s) : TEXT
Reported By: Mikael Abrahamsson
Date Reported: 2019-08-26
Section 5.3 says:
However, as not all service providers will be able to increase their link MTU, the B4 element MUST perform fragmentation and reassembly if the outgoing link MTU cannot accommodate the extra IPv6 header. The original IPv4 packet is not oversized. The packet is oversized after the IPv6 encapsulation. The inner IPv4 packet MUST NOT be fragmented. Fragmentation MUST happen after the encapsulation of the IPv6 packet. Reassembly MUST happen before the decapsulation of the IPv4 packet. A detailed procedure has been specified in [RFC2473] Section 7.2.
I do not have a corrected text. The above text doesn't say what RFC2473 section 7.2 says, so... what should it be? RFC2473 7.2 says to use the DF bit and decide whether to inner fragment or drop+send ICMP error. The above text seems to make normative statements that counter at least the DF=1 case in RFC2473 7.2. Also the text above says "Fragmentation MUST happen after the encapsulation of the IPv6 packet.". The IPv6 packet isn't encapsulated, so that sentence should be changed?