Dear Jacni, Just after reading RFC 1981, I think fragmentation of IPv6 is needed. In section 5.1, it says, "It is possible that a packetization layer, perhaps a UDP application outside the kernel, is unable to change the size of messages it sends. This may result in a packet size that exceeds the Path MTU. To accommodate such situations, IPv6 defines a mechanism that allows large payloads to be divided into fragments, with each fragment sent in a separate packet (see [IPv6-SPEC] section "Fragment Header")."
If the node which makes PMTU is the multicast source, it can change the size of message when the size exceeds the PMTU value. However, mAFTR, as a router, is unable to change the size of the message. Here is an example: An IPv4 packet is sent from the multicast source to mAFTR with size of 1000, while the IPv6 PMTU for mAFTR and mB4 is 960, how does mAFTR forward the packet? One possible way is to make IPv6 fragmentation, with two fragments: one is 960 and the other is 40 with "IPv6 Fragment Header". In addition, there may be also other ways to avoid fragmentation, e.g., cache in mAFTR as defined in [draft-jiang-behave-v4v6mc-proxy]. Best Regards, Tina TSOU http://tinatsou.weebly.com/contact.html From: Jacni Qin [mailto:jac...@gmail.com] Sent: Thursday, August 25, 2011 9:41 PM To: Tina TSOU Cc: softwires@ietf.org Subject: Re: [Softwires] Comments on section 6.3 of draft-qin-softwire-dslite-multicast-04 Hi, On Fri, Aug 26, 2011 at 10:36 AM, Tina TSOU <tina.tsou.zout...@huawei.com<mailto:tina.tsou.zout...@huawei.com>> wrote: Hi all, In section 6.3, "To avoid fragmentation, a service provider may increase the MTU size by 40 bytes on the IPv6 network or mAFTR and mB4 may use IPv6 Path MTU discovery." How to use IPv6 Path MTU discovery to avoid fragmentation? Jacni>: You can read RFC1981, thanks. Cheers, Jacni Best Regards, Tina TSOU http://tinatsou.weebly.com/contact.html _______________________________________________ Softwires mailing list Softwires@ietf.org<mailto:Softwires@ietf.org> https://www.ietf.org/mailman/listinfo/softwires
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