# reliable off-line protocol detection **URL:** \ **Category:** Zeek\ **Created:** [August 26, 2005, 10:21pm UTC](https://community.zeek.org/t/reliable-off-line-protocol-detection/847 "2005-08-26T22:21:24Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Vern](https://yyz1.discourse-cdn.com/flex011/user_avatar/community.zeek.org/vern/32/630_2.png) [@Vern](https://community.zeek.org/u/Vern)\ **Post date:** [August 26, 2005, 10:21pm UTC](https://community.zeek.org/t/reliable-off-line-protocol-detection/847/1 "2005-08-26T22:21:24Z")
> smtp.dump > > \> 1124785239.632272 127.0.0.1/56034 \> 127.0.0.1/778 ftp-sig > \> 1124785306.080354 127.0.0.1/56037 \> 127.0.0.1/778 ftp-sig > \> 1124785591.602025 127.0.0.1/56048 \> 127.0.0.1/778 ftp-sig > \> 1124785606.143460 127.0.0.1/56050 \> 127.0.0.1/778 ftp-sig > > WHY? ( =A91992 Annie Lennox) The FTP backdoor detector isn't precise - it looks for initial 220 or 426 replies, which SMTP servers can generate too. Ideally, the SMTP detector would trigger first (based on seeing EHLO or HELO). If you have a simple trace that shows it's failing to do so, go ahead and send it to me and I'll see what's up.     Vern ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/zeek/original/1X/f09d732bc2cc7c7cc7e35db67cf4e1d5233ce7a7.png) [@system](https://community.zeek.org/u/system)\ **Post date:** [May 6, 2022, 3:37pm UTC](https://community.zeek.org/t/reliable-off-line-protocol-detection/847/2 "2022-05-06T15:37:39Z")