fredy:

• Device problem occurs on
  TP-LINK C20 (AC750) v4

• Software versions of OpenWrt/LEDE release, packages, etc.
  OpenWrt 18.06.1 r7258-5eb055306f
  Kernel 4.14.63
  OpenVPN 2.4.5 mipsel-openwrt-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [MH/PKTINFO] [AEAD]
  library versions: OpenSSL 1.0.2p 14 Aug 2018, LZO 2.10

• Steps to reproduce
  Configure 2 sides using the uci format (exemple below) using the "option comp_lzo yes" and they will not connect or pass any traffic. When this option is removed it then connects

I have installed this version of OpenWrt on this hardware and tried to bring up a P2P OpenVPN as done before with other OpenWrt routers (other versions of hardware and OpenWrt). After a lot of troubleshooting I found that when running it with "option comp_lzo yes" it never works.

In one of the troubleshoots I have done I have used this configuration at both sides:

Server

config openvpn myvpn
option port 1194
option proto udp
option dev tun0
option keepalive "10 60"
option persist_key 1
option persist_tun 1
option cipher AES-128-CBC
option secret /etc/config/mykey.key
option ifconfig "10.0.0.1 10.0.0.2"
list route "192.168.1.0 255.255.255.0"
list push "redirect-gateway def1"
option comp_lzo yes
option enabled 1

Client

/usr/sbin/openvpn --remote myhostname.zapto.org --proto udp --port 1194 --dev tun0 --cipher AES-128-CBC --secret /root/mykey.key --keepalive 10 60 --ping-timer-rem --persist-tun --persist-key --ifconfig 10.0.0.2 10.0.0.1 --route 192.168.2.0 255.255.255.0 10.0.0.21 --comp-lzo --push redirect-gateway def1 --script-security 2

RESULTS

• I get the following on the client side:

Tue Oct 30 03:50:54 2018 Bad LZO decompression header byte: 69
Tue Oct 30 03:50:55 2018 Bad LZO decompression header byte: 69
Tue Oct 30 03:50:56 2018 Bad LZO decompression header byte: 69
Tue Oct 30 03:50:56 2018 Bad LZO decompression header byte: 40

Software Versions

• I have been using in this way between several routers and versions of OpenWrt and never had such problem, only in 18.06.1 and in TP-Link C20 v4. Find below the version of software in each of the routers for comparison:

This Router (doesn't work) - TP-Link C20 v4 -> library versions: OpenSSL 1.0.2p 14 Aug 2018, LZO 2.10
Router 2 (works)- Debian 8, armv7l, Kernel 3.4.39 -> library versions: OpenSSL 1.0.1t 3 May 2016, LZO 2.08
Router 3 (works) - Debian 7.9, armv6l, 4.1.13+ -> library versions: OpenSSL 1.0.2g 1 Mar 2016, LZO 2.08
Router 4 (works) - TP-Link TL-WDR3600 v1, LEDE 17.01.4, r3560-79f57e422d, mips, Kernel 4.4.92 -> library versions: OpenSSL 1.0.2n 7 Dec 2017, LZO 2.10
Router 5 (works) - TP-Link TL-WDR3600 v1, OpenWrt Chaos Calmer 15.05.1, mips, Kernel 3.18.23 -> library versions: OpenSSL 1.0.2g 1 Mar 2016, LZO 2.08

*works - between all of them, except with the TP-Link C20 v4 running 18.06.1

Another test running directly in command line

• I have done an ad-hoc test running in the command line and it seemed to work. It was between this router and a Windows 10 Machine. However when running using the UCI configuration it gives me the LZO decompression header problem. See below the two configuration

Server side (this router)

/usr/sbin/openvpn --proto udp --lport 1400 --dev tun10 --cipher AES-128-CBC --secret /root/mykey.key --keepalive 10 60 --ping-timer-rem --persist-tun --persist-key --ifconfig 192.168.14.1 192.168.14.2 --comp-lzo --push "redirect-gateway def1"

Client Side (Windows 10)

proto udp
dev tun
remote myhostname.zapto.org
port 1400
cipher AES-128-CBC
keepalive 10 60
ping-timer-rem
persist-tun
persist-key
comp-lzo
tun-mtu 1500
mssfix 1300
ifconfig 192.168.14.2 192.168.14.1

Now using the UCI OpenWrt configuration (same Client configuration above)

Server

config openvpn remote
option enabled 1
option port 1400
option proto udp
option dev tun10
option keepalive "10 60"
option persist_key 1
option persist_tun 1
option cipher AES-128-CBC
option secret /etc/config/mykey.key
option ifconfig "192.168.14.1 192.168.14.2"
list push "redirect-gateway def1"

Result

Tue Oct 30 10:53:38 2018 Bad LZO decompression header byte: 42
Tue Oct 30 10:53:48 2018 Bad LZO decompression header byte: 42
Tue Oct 30 10:53:58 2018 Bad LZO decompression header byte: 42