在使用tun模式做透明代理流量很大的情况下，会触发panicked
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Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 48/100
- Issue type
- Bug
- Clarity
- Mostly clear
- Activity status
- Quiet
- Tech stack
- rust
- Domain
- networking
Research direction
Reproduce tun-mode operation under sustained high-volume TCP traffic on the reported shadowsocks-rust 1.24.0 and OpenWrt environment. Start at the smoltcp 0.12.0 panic reported in src/wire/tcp.rs:81 and use RUST_BACKTRACE=1 to trace the relevant path; done means the traffic no longer triggers sequence-number underflow or a panic.
Written by the indexing model from the issue text.
Description
非常感谢作者带来了tun模式，tun模式对于我一台老旧路由器的精简openwrt内核有着非常重要的作用，因为该路由器官方固件没有tproxy，甚至ipset也并未编译进系统，导致udp协议无法使用。
但是tun模式的出现拯救了我这台老旧路由器，代理效率（即速度）超出原本的期待。
回归到问题，该故障现象出现的时候有如下报错：
thread 'smoltcp-poll' (17908) panicked at /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/smoltcp-0.12.0/src/wire/tcp.rs:81:13:
attempt to subtract sequence numbers with underflow
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace
如标题所述，该故障现象仅当在流量大的情况下出现，应该是TCP流量，UDP流量暂时没法测。
它不是随机偶尔出现，是一定会伴随着在大流量的情况出现的。
shadowsocks-rust版本是：
INFO shadowsocks local 1.24.0 build 2025-12-11T00:30:22.902795962+00:00
官方固件的openwrt版本是这个：
root@WRT32X:~# uname -a
Linux WRT32X 4.4.14 #4 SMP Wed Apr 4 18:23:44 UTC 2018 armv7l GNU/Linux
希望该issue能得到调查和修正。非常感谢！
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