experimental support for IPv4 unicast extensions
- Reply: George Michaelson : "Re: experimental support for IPv4 unicast extensions"
- Go to: [ bottom of page ] [ top of archives ] [ this month ]
Date: Wed, 06 Jul 2022 22:06:30 UTC
I have been corresponding with the authors of Internet-Drafts that relax restrictions on parts of the IPv4 address space to allow normal unicast use, and I have FreeBSD changes to allow experimentation with these updates. This message summarizes my changes, and solicits input. The changes are all controlled by sysctl, and default to "off". The parts of the address space in question and the relevant changes: 0/8 (network 0) : Restrictions on network 0 are lifted if the sysctl net.inet.ip.allow_zeronet is set to 1. This applies to packet forwarding and ICMP echo. 224/4 (Experimental/"Class E") : Restrictions on the Experimental address class are lifted if the sysctl net.inet.ip.allow_experimental is set to 1. This applies to packet forwarding and ICMP echo. 127/8 (loopback net) : The size of the reservation for the loopback network can be reduced from 127/8 to 127.0/16 using the sysctl net.int.ip.loopback_mask. My current sysctl sets the mask, but that is a little cumbersome; I should probably change the sysctl to allow a mask length to be set. This change is limited to the kernel; the IN_LOOPBACK macro uses the current mask in the kernel, but the default mask at user level. Also, some user programs use IN_LOOPBACKNET along with a Class A shift to crack this by hand. The kernel change affects IP packet input and output as well as forwarding. The changes described above are all included in a single review for now, although I would probably separate them before pushing them. (They necessarily collide though.) The review is intended for comments only, and is https://reviews.freebsd.org/D35741. I think it makes sense to put these changes in -current in order to enable experimentation, but I wanted to open the subject for discussion first. Changes are also being made in Linux, although I don't know their state. Note that there is a related proposal and change to allow use of the lowest host on a network/subnet . This change was essentially a bug fix for FreeBSD, and is already in -current and 13.1-RELEASE. Mike  https://datatracker.ietf.org/doc/draft-schoen-intarea-unicast-0/01/  https://datatracker.ietf.org/doc/draft-schoen-intarea-unicast-240/  https://datatracker.ietf.org/doc/draft-schoen-intarea-unicast-127/  https://datatracker.ietf.org/doc/draft-schoen-intarea-unicast-lowest-address/