WORKAROUND: if the other application which needs to bind to a UDP port can be configured to bind to a specific interface, then you can make isc-dhcp-server bind to a different interface in dhcpd.conf. e.g.
ddns-local-address4 127.0.0.1; ddns-local-address6 ::1; -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to isc-dhcp in Ubuntu. https://bugs.launchpad.net/bugs/1670303 Title: dhcpd does not respect ip_local_port _range or ip_local_reserved_ports Status in isc-dhcp package in Ubuntu: New Bug description: When isc-dhcp-server starts up, in addition to listening on port 67, it binds to a random UDP port on an IPv4 socket and another on an IPv6 socket: # netstat -naup | grep dhcp udp 0 0 0.0.0.0:11075 0.0.0.0:* 8188/dhcpd udp 0 0 0.0.0.0:67 0.0.0.0:* 8188/dhcpd udp6 0 0 :::10800 :::* 8188/dhcpd # (I am guessing this is for making outbound DNS queries?) However, this prevented a later application of mine from working, as it wanted to bind to port 11075 for accepting incoming data. Simply doing "service isc-dhcp-server restart" makes it choose new ports, but this problem may occur again in the future. In the default configuration, I believe ephemeral ports should only use 32768 and above: # cat /proc/sys/net/ipv4/ip_local_port_range 32768 60999 # cat /proc/sys/net/ipv4/ip_local_reserved_ports # I also tried setting a reservation, and this was not respected either. # sysctl net.ipv4.ip_local_reserved_ports="10000-59999" net.ipv4.ip_local_reserved_ports = 10000-59999 After restarting dhcpd: # netstat -naup | grep dhcp udp 0 0 0.0.0.0:50610 0.0.0.0:* 4592/dhcpd udp 0 0 0.0.0.0:67 0.0.0.0:* 4592/dhcpd udp6 0 0 :::28891 :::* 4592/dhcpd I can find no way to tell isc-dhcp-server which port range to use. Setting "omapi-port" in dhcpd.conf makes it listen for *TCP* connections on the given port, and does not affect the UDP behaviour. I don't know if this is a problem with the application (explicitly picking a local port), the resolver library (ditto), or the kernel (ignoring its own ip_local_port_range) ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: isc-dhcp-server 4.3.3-5ubuntu12.6 ProcVersionSignature: Ubuntu 4.4.0-64.85-generic 4.4.44 Uname: Linux 4.4.0-64-generic x86_64 ApportVersion: 2.20.1-0ubuntu2.5 Architecture: amd64 Date: Mon Mar 6 09:30:29 2017 DhServerLeases: InstallationDate: Installed on 2017-03-04 (2 days ago) InstallationMedia: Ubuntu-Server 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.8) ProcEnviron: SHELL=/bin/bash TERM=xterm-256color PATH=(custom, no user) LANG=en_US LANGUAGE=en_US: SourcePackage: isc-dhcp UpgradeStatus: No upgrade log present (probably fresh install) mtime.conffile..etc.dhcp.dhcpd.conf: 2017-03-04T09:46:07.987046 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1670303/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
