DNS响应超过512B导致某些操作系统nslookup查询失败 #1417
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Operating system
Linux
System version
openwrt linux 5.15
Installation type
Original sing-box Command Line
If you are using a graphical client, please provide the version of the client.
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Version
Description
在使用sing-box udp dns查询过程中，当响应体超过512B时，某些操作系统（例如openwrt）使用nslookup程序查询dns会返回解析错误。在 #991 中已经提到相关问题，但当时只看到了现象不明确原因，后来issue被搁置了，在这边重开一个，之前的已经关掉了
使用下面复现步骤对512.size.dns.netmeister.org进行查询（这个域名无意义，仅作为测试使用，实际情况可以用cn-beijing-data.aliyundrive.net进行测试）
我尝试修改源码，截取部分dns响应结果，可以正确解析
在不使用sing-box情况下，直接进行dns查询，即便响应体超过512B也不会出错
~$ nslookup 512.size.dns.netmeister.org Server: 127.0.0.1 Address: 127.0.0.1:53 Non-authoritative answer: Non-authoritative answer: Name: 512.size.dns.netmeister.org Address: 127.0.0.17 Name: 512.size.dns.netmeister.org Address: 127.0.0.10 Name: 512.size.dns.netmeister.org Address: 127.0.0.18 Name: 512.size.dns.netmeister.org Address: 127.0.0.22 Name: 512.size.dns.netmeister.org Address: 127.0.0.24 Name: 512.size.dns.netmeister.org Address: 127.0.0.2 Name: 512.size.dns.netmeister.org Address: 127.0.0.4 Name: 512.size.dns.netmeister.org Address: 127.0.0.12 Name: 512.size.dns.netmeister.org Address: 127.0.0.19 Name: 512.size.dns.netmeister.org Address: 127.0.0.26 Name: 512.size.dns.netmeister.org Address: 127.0.0.0 Name: 512.size.dns.netmeister.org Address: 127.0.0.16 Name: 512.size.dns.netmeister.org Address: 127.0.0.9 Name: 512.size.dns.netmeister.org Address: 127.0.0.6 Name: 512.size.dns.netmeister.org Address: 127.0.0.8 Name: 512.size.dns.netmeister.org Address: 127.0.0.1 Name: 512.size.dns.netmeister.org Address: 127.0.0.15 Name: 512.size.dns.netmeister.org Address: 127.0.0.3 Name: 512.size.dns.netmeister.org Address: 127.0.0.21 Name: 512.size.dns.netmeister.org Address: 127.0.0.5 Name: 512.size.dns.netmeister.org Address: 127.0.0.20 Name: 512.size.dns.netmeister.org Address: 127.0.0.25 Name: 512.size.dns.netmeister.org Address: 127.0.0.14 Name: 512.size.dns.netmeister.org Address: 127.0.0.7 Name: 512.size.dns.netmeister.org Address: 127.0.0.11 Name: 512.size.dns.netmeister.org Address: 127.0.0.23 Name: 512.size.dns.netmeister.org Address: 127.0.0.13 Name: 512.size.dns.netmeister.org Address: 127.0.0.27总结一下，不使用sing-box对512.size.dns.netmeister.org进行查询能够解析，使用sing-box对512.size.dns.netmeister.org进行查询不能解析，修改代码截取部分响应也可以解析。不过查资料对不能解析的定位又是“响应体超过512B”的原因，猜测直接响应和sing-box解析重构的响应有某些参数差别导致一个被接受一个不被接受。以我目前的知识储备不足以弄清楚这个问题，想请教下这个问题算不算sing-box的bug
相关参考资料
Reproduction
使用此配置运行sing-box，在linux中用
nslookup 512.size.dns.netmeister.org 127.0.0.1:1053进行dns查询，返回解析错误{ "log": { "level": "trace" }, "inbounds": [ { "tag": "in-dns", "type": "direct", "listen": "::", "listen_port": 1053 } ], "outbounds": [ { "tag": "out-direct", "type": "direct" }, { "tag": "out-dns", "type": "dns" } ], "dns": { "servers": [ { "tag": "dns-direct", "detour": "out-direct", "address": "223.5.5.5" } ], "final": "dns-direct", "strategy": "ipv4_only" }, "route": { "rules": [ { "inbound": "in-dns", "outbound": "out-dns" } ], "final": "out-direct" } }Logs
Integrity requirements
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