IPv6AcceptRA: RDNSS Lifetime is not expiring

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:

 

1. Router:  Send RA [RDNSS address of “nameserver60s”, lifetime: “60”]
2. Host: “resolvectl” shows the link’s DNS server now lists the RDNSS address of “nameserver60s”
3. ** Wait for more than 60 seconds – the RDNSS entry should expire **
4. Host:
1. “resolvectl” continues to list the address of “nameserver60s” on the link.
2. 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.