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So I was testing a router and it added some random IPv6 addresses to all the machines on my network, including my DNS server. Somehow those IPs were broadcasted around as valid DNS servers (not sure how as only the real router sends IPv6 RA packets) but long story short, now all my machines are sending DNS queries to an IP address that doesn't exist.

If I restart resolved with systemctl restart systemd-resolved then resolvectl still shows these bogus IPs as valid name servers.

They are listed in /etc/resolv.conf so if I delete them there and restart systemd-resolved it just adds the bogus IPs back in again.

If I look in the logs with journalctl --unit=systemd-resolved then it tells me the bogus IPs are operating in "degraded feature mode" but doesn't tell me where it found those IPs to begin with.

Where is it picking up these wrong IP addresses from?? Is there some cache file I need to delete to make it go back to only using the IPs supplied from the IPv6 router advertisements only?

ipv6 systemd-resolved

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asked 2 hours ago

MalvineousMalvineous

2,16512135

add a comment | 

0

So I was testing a router and it added some random IPv6 addresses to all the machines on my network, including my DNS server. Somehow those IPs were broadcasted around as valid DNS servers (not sure how as only the real router sends IPv6 RA packets) but long story short, now all my machines are sending DNS queries to an IP address that doesn't exist.

If I restart resolved with systemctl restart systemd-resolved then resolvectl still shows these bogus IPs as valid name servers.

They are listed in /etc/resolv.conf so if I delete them there and restart systemd-resolved it just adds the bogus IPs back in again.

If I look in the logs with journalctl --unit=systemd-resolved then it tells me the bogus IPs are operating in "degraded feature mode" but doesn't tell me where it found those IPs to begin with.

Where is it picking up these wrong IP addresses from?? Is there some cache file I need to delete to make it go back to only using the IPs supplied from the IPv6 router advertisements only?

ipv6 systemd-resolved

share|improve this question

asked 2 hours ago

MalvineousMalvineous

2,16512135

add a comment | 

So I was testing a router and it added some random IPv6 addresses to all the machines on my network, including my DNS server. Somehow those IPs were broadcasted around as valid DNS servers (not sure how as only the real router sends IPv6 RA packets) but long story short, now all my machines are sending DNS queries to an IP address that doesn't exist.

If I restart resolved with systemctl restart systemd-resolved then resolvectl still shows these bogus IPs as valid name servers.

They are listed in /etc/resolv.conf so if I delete them there and restart systemd-resolved it just adds the bogus IPs back in again.

If I look in the logs with journalctl --unit=systemd-resolved then it tells me the bogus IPs are operating in "degraded feature mode" but doesn't tell me where it found those IPs to begin with.

Where is it picking up these wrong IP addresses from?? Is there some cache file I need to delete to make it go back to only using the IPs supplied from the IPv6 router advertisements only?

ipv6 systemd-resolved

share|improve this question

asked 2 hours ago

MalvineousMalvineous

2,16512135

share|improve this question

asked 2 hours ago

MalvineousMalvineous

2,16512135

share|improve this question

asked 2 hours ago

MalvineousMalvineous

2,16512135

asked 2 hours ago

MalvineousMalvineous

2,16512135

asked 2 hours ago

MalvineousMalvineous

2,16512135

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You may use this command: sudo systemd-resolve --flush-caches

To verify that flush was sucessfull, use: sudo systemd-resolve --statistics

Sample output:

Cache

  Current Cache Size: 0

          Cache Hits: 101

        Cache Misses: 256

Answer taken from https://askubuntu.com/questions/906476/how-can-i-flush-the-dns-on-ubuntu-17-04 and reproduced here.

Google keywords used to find that page:

systemd-resolved flush cache

First result.

share

answered 4 mins ago

thecarpythecarpy

2,7001028

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You may use this command: sudo systemd-resolve --flush-caches

To verify that flush was sucessfull, use: sudo systemd-resolve --statistics

Sample output:

Cache

  Current Cache Size: 0

          Cache Hits: 101

        Cache Misses: 256

Answer taken from https://askubuntu.com/questions/906476/how-can-i-flush-the-dns-on-ubuntu-17-04 and reproduced here.

Google keywords used to find that page:

systemd-resolved flush cache

First result.

share

answered 4 mins ago

thecarpythecarpy

2,7001028

add a comment | 

0

You may use this command: sudo systemd-resolve --flush-caches

To verify that flush was sucessfull, use: sudo systemd-resolve --statistics

Sample output:

Cache

  Current Cache Size: 0

          Cache Hits: 101

        Cache Misses: 256

Answer taken from https://askubuntu.com/questions/906476/how-can-i-flush-the-dns-on-ubuntu-17-04 and reproduced here.

Google keywords used to find that page:

systemd-resolved flush cache

First result.

share

answered 4 mins ago

thecarpythecarpy

2,7001028

add a comment | 

You may use this command: sudo systemd-resolve --flush-caches

To verify that flush was sucessfull, use: sudo systemd-resolve --statistics

Sample output:

Cache

  Current Cache Size: 0

          Cache Hits: 101

        Cache Misses: 256

Answer taken from https://askubuntu.com/questions/906476/how-can-i-flush-the-dns-on-ubuntu-17-04 and reproduced here.

Google keywords used to find that page:

systemd-resolved flush cache

First result.

share

answered 4 mins ago

thecarpythecarpy

2,7001028

Cache

  Current Cache Size: 0

          Cache Hits: 101

        Cache Misses: 256

share

answered 4 mins ago

thecarpythecarpy

2,7001028

answered 4 mins ago

thecarpythecarpy

2,7001028

answered 4 mins ago

thecarpythecarpy

2,7001028