Re: IPv6AcceptRA: RDNSS Lifetime is not expiring

Petr Menšík <pemensik@xxxxxxxxxx> · Mon, 17 Jul 2023 11:39:32 +0200



    I would suggest creating issue at github.com/systemd/systemd
      repository. I have not tested it, but sounds like it should be
      fixed.

    
    On 12. 07. 23 0:39, Muggeridge, Matt
      wrote:

    
        Hello there!
         
        In our IPv6 network, the address of a
          Recursive DNS Server (RDNSS) is supplied in a Router
          Advertisement (RA), with a lifetime of 60 seconds.
         
        It appears that RDNSS lifetime is not being
          honoured (RFC 8106, section 5.1).  I
          reviewed the code and can see where the RDNSS lifetime is being saved,
          though I was unable to determine how it was being handled upon
          expiry.
         
        How do I configure networkd so that the
          RA’s RDNSS lifetime is honoured?
         
        Here is a summary of the simple protocol
          exchange:
         
        
          Router: 
            Send RA [RDNSS address of “nameserver60s”, lifetime: “60”]
          Host:
            “resolvectl” shows the link’s DNS server now lists the RDNSS
            address of “nameserver60s”
          ** Wait for
            more than 60 seconds – the RDNSS entry should expire **
          Host:
          
            “resolvectl”
              continues to list the address of “nameserver60s” on the
              link.
            Using
              tcpdump to trace “ping test.example.com”, the
              “nameserver60s” is still being used.  It never timed out.
          
        
        Here is my network configuration, showing
          UseDNS and UseDomains both set to “yes”:
         
        ------------------------------------------------------------
        $ cat /etc/systemd/network/10-eno0.network
          
        [Match]
        KernelCommandLine=!nfsroot
        Name=eno0
         
        [DHCP]
        ClientIdentifier=mac
        RouteMetric=10
        UseDomains=yes
        UseHostname=yes
        UseMTU=yes
         
        [Network]
        #DHCP=ipv6
        Address=10.1.1.1/24
        #DNS=1.2.3.6
        Gateway=1.1.1.2
        IPv6AcceptRA=yes
         
        [IPv6AcceptRA]
        UseDNS=yes
        UseDomains=yes
        ------------------------------------------------------------
         
        Grateful for any suggestions.
         
        Kind regards,
        Matt.
        PS: We’re on systemd 250.  I’ve searched
          later versions of the
          release notes and it seems there
          have been no changes in this area.
         
         
    -- 
Petr Menšík
Software Engineer, RHEL
Red Hat, http://www.redhat.com/
PGP: DFCF908DB7C87E8E529925BC4931CA5B6C9FC5CB