Interface bind causes only IPv6 peer/tracker can be connected with dual stack

[zhangweilst]

qBittorrent & operating system versions

qBittorrent: 5.0.1 nox
Operating system: Ubuntu 24.04 LTS
Qt: 6.8.0
libtorrent-rasterbar: 2.0.10.0

What is the problem?

Interface settings:

$ ip a
9: br2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 0e:3a:99:6a:e3:66 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.2/16 brd 10.0.255.255 scope global br2
       valid_lft forever preferred_lft forever
    inet6 2409:xxx::bad:babe/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 2591792sec preferred_lft 604592sec

qBittorrent options (Options -> Advanced):

Network interface: br2
Optional IP address to bind to: All addresses

What happens:

• All peers are IPv6. Some IPv4 addresses appear, but disappear soon after several seconds
• IPv4 only tracker will be "Host is unreachable"
• The tracker is accessible from command line (e.g. wget --bind-address=10.0.0.2 https://tracker.sjtu.edu.cn)
• SYN_SENT can be seen for IPv4, but never ESTABLISHED. Both true for peers and tracker.

Steps to reproduce

No response

Additional context

No response

Log(s) & preferences file(s)

[Application]
FileLogger\Age=1
FileLogger\AgeType=1
FileLogger\Backup=true
FileLogger\DeleteOld=true
FileLogger\Enabled=true
FileLogger\MaxSizeBytes=66560
FileLogger\Path=/root/.local/share/qBittorrent/logs
MemoryWorkingSetLimit=4096

[AutoRun]
OnTorrentAdded\Enabled=false
OnTorrentAdded\Program=
enabled=false
program=

[BitTorrent]
Session\AddTorrentStopped=false
Session\AlternativeGlobalDLSpeedLimit=102400
Session\AlternativeGlobalUPSpeedLimit=8192
Session\DefaultSavePath=/data03/qbit/general
Session\ExcludedFileNames=
Session\Interface=br2
Session\InterfaceAddress=
Session\InterfaceName=br2
Session\MaxConnections=1000
Session\MaxUploads=100
Session\MaxUploadsPerTorrent=10
Session\PerformanceWarning=true
Session\Port=37001
Session\QueueingSystemEnabled=false
Session\ReannounceWhenAddressChanged=true
Session\SSL\Port=43568
Session\ShareLimitAction=Stop
Session\UseAlternativeGlobalSpeedLimit=false

[Core]
AutoDeleteAddedTorrentFile=Never

[LegalNotice]
Accepted=true

[Meta]
MigrationVersion=8

[Network]
PortForwardingEnabled=false
Proxy\HostnameLookupEnabled=false
Proxy\Profiles\BitTorrent=true
Proxy\Profiles\Misc=true
Proxy\Profiles\RSS=true

[Preferences]
Advanced\RecheckOnCompletion=false
Advanced\trackerPort=9000
Advanced\trackerPortForwarding=false
Connection\ResolvePeerCountries=true
DynDNS\DomainName=changeme.dyndns.org
DynDNS\Enabled=false
DynDNS\Password=
DynDNS\Service=DynDNS
DynDNS\Username=
General\Locale=en
MailNotification\email=
MailNotification\enabled=false
MailNotification\password=
MailNotification\req_auth=true
MailNotification\req_ssl=false
MailNotification\sender=[email protected]
MailNotification\smtp_server=smtp.changeme.com
MailNotification\username=
WebUI\Address=*
WebUI\AlternativeUIEnabled=false
WebUI\AuthSubnetWhitelist=@invalid()
WebUI\AuthSubnetWhitelistEnabled=false
WebUI\BanDuration=3600
WebUI\CSRFProtection=true
WebUI\ClickjackingProtection=true
WebUI\CustomHTTPHeaders=
WebUI\CustomHTTPHeadersEnabled=false
WebUI\HTTPS\CertificatePath=
WebUI\HTTPS\Enabled=false
WebUI\HTTPS\KeyPath=
WebUI\HostHeaderValidation=true
WebUI\LocalHostAuth=false
WebUI\MaxAuthenticationFailCount=5
WebUI\Password_PBKDF2="redacted"
WebUI\Port=redacted
WebUI\ReverseProxySupportEnabled=false
WebUI\RootFolder=
WebUI\SecureCookie=true
WebUI\ServerDomains=*
WebUI\SessionTimeout=3600
WebUI\TrustedReverseProxiesList=
WebUI\UseUPnP=false
WebUI\Username=redacted

[zhangweilst]

To further explain the problem, when "Optional IP address to bind to" is set to "All IPv4 addresses", the IPv4 funcionality is all fine. Peers are all IPv4 and can download/upload, and trackers can be connected normally!

[zhangweilst]

I'll provide more details if necessary. Binding to an interface is absolutely necessary for me, since I want none of the BT traffic goes through my VPN. Hope can help address this issue for others too!