netdev - ftp ipvs connect failed in ipv6

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Message-ID: <e1527ca5f8f84be09022859f5e33b584@huawei.com>
Date: Mon, 10 Feb 2025 13:06:11 +0000
From: mengkanglai <mengkanglai2@...wei.com>
To: Pablo Neira Ayuso <pablo@...filter.org>, Jozsef Kadlecsik
	<kadlec@...filter.org>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
	"coreteam@...filter.org" <coreteam@...filter.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "Yanan (Euler)" <yanan@...wei.com>, "Fengtao (fengtao, Euler)"
	<fengtao40@...wei.com>, "gaoxingwang (A)" <gaoxingwang1@...wei.com>
Subject: ftp ipvs connect failed in ipv6

Hello:
I found a problem with ftp ipvs.
I create 3 virtual machine in one host. One is the FTP client, the other is the ipvs transition host, and the other is the FTP server.
The ftp connection is successful in ipv4 address,but failed in ipv6 address.
The failure is tcp6 checksum error in tcp_dnat_handler(tcp_dnat_handler-> tcp_csum_check->csum_ipv6_magic),
I trace back where skb->csum is assigned and found skb->csum is assigned in nf_ip6_checksum in case CHECKSUM_NONE(ipv6_conntrack_in=> nf_conntrack_in => nf_conntrack_tcp_packet => nf_ip6_checksum).
I don't know much about ipv6 checksums,why ipv6 nf_conntrack assign skb->csum but check error in ipvs tcp_dnat_handler?
Best wishes!