I was able to identify from where the port range list is initialize, and the decision is taken by binary package "libdns162" (source package "bind9")[1] which dhclient relies on. Basically, it randomly takes any port available between 1024 and 65535[2]
So there is a port randomization mechanism made by the library that take the decision instead of, for instance in some other cases, where the decision is leave it to the kernel[3]. In this particular case both sysctl options : net.ipv4.ip_local_port_range net.ipv4.ip_local_reserved_ports have no effect on port assignation decision. [1] - https://github.com/wklaebe/bind9/blob/ac1dcdd124a5abdec4969e2c33836d863bf73aa7/lib/dns/dispatch.c#L1921 [2] - https://tools.ietf.org/html/rfc6335 [3] - Example : net.ipv4.ip_local_port_range = 32768 60999 Regards, -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1176046 Title: isc-dhcp dhclient listens on extra random ports To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1176046/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
