Frequent dhclient DHCPREQUEST messages in syslog

[yanggis]

I setup a softether vpn server on ubuntu server. Initially, everything works fine. I can connect the ubuntu server remotely from another ubuntu client. However, recently, I found tons of dhclient DHCPREQUEST messages in syslog indicating that dhclient is sending a DHCPREQUEST on vpn_soft_vpn to 192.168.30.1. Once these message start, they repeat approximately every 1 second.
Something likes this:
Mar 3 22:54:07 XK dhclient[8545]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0xa027abf)
Mar 3 22:54:07 XK dhclient[9080]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x462c3792)
Mar 3 22:54:11 XK dhclient[3252]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x2be20562)
Mar 3 22:54:11 XK dhclient[2909]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x2496151f)
Mar 3 22:54:12 XK dhclient[3047]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x2b8914c0)
Mar 3 22:54:12 XK dhclient[7897]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x3baf17f9)
Mar 3 22:54:13 XK dhclient[4473]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x409d0433)
Mar 3 22:54:14 XK dhclient[1865]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x7f45b09b)
Mar 3 22:54:15 XK dhclient[13627]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0xec18551)
Mar 3 22:54:15 XK dhclient[8193]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x2ae566f9)
Mar 3 22:54:16 XK dhclient[5010]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x4decc5a8)
Mar 3 22:54:16 XK dhclient[9080]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x462c3792)
Could please check what's wrong with the client?

[yanggis]

BTW, I'v added this rule to iptable rules on the server:
sudo iptables -A INPUT -i tap_soft -p udp --dport 67 -j ACCEPT
I also checked this rule has got some accepted packages.

[yanggis]

Now the log info output likes this:

Mar 4 01:38:34 XK dhclient[5010]: dhclient.c:2755: Failed to send 300 byte long packet over vpn_soft_vpn interface.
Mar 4 01:38:35 XK dhclient[8545]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0xa027abf)
Mar 4 01:38:35 XK dhclient[4473]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 255.255.255.255 port 67 (xid=0x409d0433)
Mar 4 01:38:35 XK dhclient[4473]: send_packet: No such device or address
Mar 4 01:38:35 XK dhclient[4473]: dhclient.c:2755: Failed to send 300 byte long packet over vpn_soft_vpn interface.
Mar 4 01:38:36 XK dhclient[8193]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x2ae566f9)
Mar 4 01:38:37 XK dhclient[4214]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 255.255.255.255 port 67 (xid=0x4c74e463)
Mar 4 01:38:37 XK dhclient[4214]: send_packet: No such device or address
Mar 4 01:38:37 XK dhclient[4214]: dhclient.c:2755: Failed to send 300 byte long packet over vpn_soft_vpn interface.
Mar 4 01:38:37 XK dhclient[3713]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 255.255.255.255 port 67 (xid=0x1f905b30)
Mar 4 01:38:37 XK dhclient[3713]: send_packet: No such device or address
Mar 4 01:38:37 XK dhclient[3713]: dhclient.c:2755: Failed to send 300 byte long packet over vpn_soft_vpn interface.
Mar 4 01:38:38 XK dhclient[2909]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 255.255.255.255 port 67 (xid=0x2496151f)
Mar 4 01:38:38 XK dhclient[2909]: send_packet: No such device or address
Mar 4 01:38:38 XK dhclient[2909]: dhclient.c:2755: Failed to send 300 byte long packet over vpn_soft_vpn interface.
Mar 4 01:38:39 XK dhclient[9080]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x462c3792)
Mar 4 01:38:40 XK dhclient[3047]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 255.255.255.255 port 67 (xid=0x2b8914c0)
Mar 4 01:38:40 XK dhclient[3047]: send_packet: No such device or address
Mar 4 01:38:40 XK dhclient[3047]: dhclient.c:2755: Failed to send 300 byte long packet over vpn_soft_vpn interface.
Mar 4 01:38:41 XK dhclient[7897]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0x3baf17f9)
Mar 4 01:38:41 XK dhclient[13627]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 192.168.30.1 port 67 (xid=0xec18551)
Mar 4 01:38:42 XK dhclient[3252]: DHCPREQUEST of 192.168.30.20 on vpn_soft_vpn to 255.255.255.255 port 67 (xid=0x2be20562)
Mar 4 01:38:42 XK dhclient[3252]: send_packet: No such device or address
Mar 4 01:38:42 XK dhclient[3252]: dhclient.c:2755: Failed to send 300 byte long packet over vpn_soft_vpn interface.

[PizzaProgram]

Hi,
I'm a newbee here too, and I am also experiencing huge amount of communication even if nothing happens !
Only having 2 inactive clients, connected to the server (not allowing them to go to the internet through it! )
can create a 1.5MB log file pro day = ca 5 entries / PC each second.

The server Log of ca 1 second :
(Default LOG setup: TCP conn. + DHCP packet >> both headers only.)

Code: Select all

2023-03-07,01:45:03.925,SID-MEDIA-39,SID-GAMER2022-38,5EAAF3A4E674,5E9D92524322,0x86DD,86,TCP_CONNECTv6,SYN+ACK,fe80::fefa:8208:5d5c:416f,2869,fe80::ce88:f401:c40c:b1ba,49679,507403847,1233189011,WindowSize=65535,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.127,SID-MEDIA-39,SID-GAMER2022-38,5EAAF3A4E674,5E9D92524322,0x86DD,1359,TCP_CONNECTv6,FIN+PSH+ACK,fe80::fefa:8208:5d5c:416f,2869,fe80::ce88:f401:c40c:b1ba,49679,507450077,1233190786,WindowSize=512,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.137,SID-GAMER2022-38,SID-MEDIA-39,5E9D92524322,5EAAF3A4E674,0x86DD,74,TCP_CONNECTv6,FIN+ACK,fe80::ce88:f401:c40c:b1ba,49679,fe80::fefa:8208:5d5c:416f,2869,1233190786,507451363,WindowSize=508,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.147,SID-GAMER2022-38,SID-MEDIA-39,5E9D92524322,5EAAF3A4E674,0x86DD,86,TCP_CONNECTv6,SYN,fe80::ce88:f401:c40c:b1ba,49680,fe80::fefa:8208:5d5c:416f,2869,922624293,0,WindowSize=64800,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.147,SID-MEDIA-39,SID-GAMER2022-38,5EAAF3A4E674,5E9D92524322,0x86DD,86,TCP_CONNECTv6,SYN+ACK,fe80::fefa:8208:5d5c:416f,2869,fe80::ce88:f401:c40c:b1ba,49680,3128668901,922624294,WindowSize=65535,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.178,SID-MEDIA-39,SID-GAMER2022-38,5EAAF3A4E674,5E9D92524322,0x86DD,487,TCP_CONNECTv6,FIN+PSH+ACK,fe80::fefa:8208:5d5c:416f,2869,fe80::ce88:f401:c40c:b1ba,49680,3128669130,922625198,WindowSize=510,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.188,SID-GAMER2022-38,SID-MEDIA-39,5E9D92524322,5EAAF3A4E674,0x86DD,74,TCP_CONNECTv6,FIN+ACK,fe80::ce88:f401:c40c:b1ba,49680,fe80::fefa:8208:5d5c:416f,2869,922625198,3128669544,WindowSize=511,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.188,SID-GAMER2022-38,SID-MEDIA-39,5E9D92524322,5EAAF3A4E674,0x86DD,86,TCP_CONNECTv6,SYN,fe80::ce88:f401:c40c:b1ba,49681,fe80::fefa:8208:5d5c:416f,2869,1661175827,0,WindowSize=64800,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.198,SID-MEDIA-39,SID-GAMER2022-38,5EAAF3A4E674,5E9D92524322,0x86DD,86,TCP_CONNECTv6,SYN+ACK,fe80::fefa:8208:5d5c:416f,2869,fe80::ce88:f401:c40c:b1ba,49681,994395964,1661175828,WindowSize=65535,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.218,SID-MEDIA-39,SID-GAMER2022-38,5EAAF3A4E674,5E9D92524322,0x86DD,1144,TCP_CONNECTv6,FIN+PSH+ACK,fe80::fefa:8208:5d5c:416f,2869,fe80::ce88:f401:c40c:b1ba,49681,994402632,1661176099,WindowSize=512,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:04.228,SID-GAMER2022-38,SID-MEDIA-39,5E9D92524322,5EAAF3A4E674,0x86DD,74,TCP_CONNECTv6,FIN+ACK,fe80::ce88:f401:c40c:b1ba,49681,fe80::fefa:8208:5d5c:416f,2869,1661176099,994403703,WindowSize=513,-,178.48.96.1,178.48.96.1
2023-03-07,01:45:41.602,SID-MEDIA-39,SID-GAMER2022-38,5EAAF3A4E674,5E9D92524322,0x86DD,86,TCP_CONNECTv6,SYN,fe80::fefa:8208:5d5c:416f,62490,fe80::ce88:f401:c40c:b1ba,2869,3298406281,0,WindowSize=64800,-,178.48.96.1,178.48.96.1

My clients + server are the latest developer versions (5.02 nightly builds)

I do not know, if that's supposed to be "normal". I hope not.

(At OpenVPN we did not experience such frequent traffic if we did not connect to the client. Max 1 quick refresh/reconnect every 2/10 minutes)