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Date: Thu, 19 Aug 2021 12:16:52 +0300 From: Oleg <lego12239@...dex.ru> To: Thorsten Glaser <t.glaser@...ent.de> Cc: netdev@...r.kernel.org Subject: Re: ipv6 ::1 and lo dev On Wed, Aug 18, 2021 at 07:47:37PM +0200, Thorsten Glaser wrote: > On Wed, 18 Aug 2021, Oleg wrote: > > > I try to replace ::1/128 ipv6 address on lo dev with ::1/112 to > > access more than 1 address(like with ipv4 127.0.0.1/8). But i get > > AIUI this is not possible in IPv6, only :: and ::1 are reserved, > the rest of ::/96 is IPv4-compatible IPv6 addresses. This is a big mistake of standards and, i think, we shouldn't conform to standards in this area. Because standards conflicts with real life practice (and needs) here. I think, we can safely use ::/104 as analog of 127.0.0.1/8, because, AFAIK, 0.0.0.0/8 isn't used now in practice and thus there are no problems with ipv4-mapped ipv6 addresses. In any case, we should allow users to get an expected behaviour for lo dev address - as with 127.0.0.1/8. I.e. when i remove ::1/128 and set ::1/104 i expect that ping ::2, ::3 and etc will work(may be only if some parameter for "ip a add" is specified). Unfortunately i can't suggest any patch, because my kernel programming level is about 0 :-). May be anybody can do it? > I never understood why you’d want more than one address for loopback > anyway (in my experience, the more addresses a host has, the more > confused it’ll get about which ones to use for what). Besides already mentioned cases i say you about my 2 cases: 1. We have a service which serve many tunnels to different machines (think of it as many ssh -R X:127.0.0.N:Y to our service servers). Each machine is mapped to address:port(thus it constant between sessions). And we use many addresses from 127.0.0.1/8 :-). 2. We have many qemu VMs on several hardware hosts. We assign an address to every VM from 127.0.0.1/8 for comfort use of telnet/vnc. E.g. we have in /etc/hosts something like this(where third column is for host machine index and fourth column is for VM index): ... 127.0.1.2 www1.vm 127.0.1.3 www2.vm 127.0.1.4 www3.vm 127.0.1.5 dns1.vm 127.0.1.5 dns2.vm 127.0.1.6 mail1.vm ... and run qemu with: -serial telnet:dns1.vm:23,server,nowait -vnc dns1.vm:0 This /etc/hosts syncronized between hardware hosts and if one if it fail we can migrate all VMs from it to another one and their addresses aren't intermixed. -- Олег Неманов (Oleg Nemanov)
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