Forcing SIP clients to provider's PPPoE Peer-DNS

RouterOS General
1

Hi,

I’m a customer of Deutsche Telekom und using their VoIP service. They tend to assign one of their SIP servers to a specific customer and the provider’s PPPoE Peer DNS will always resolve the URL to the correct server IP address on their site. The problem is whenever using public DNS servers, they tend to resolve to other IP addresses of Deutsche Telekom servers (simply using one in the pool of available servers) which causes the SIP connection to break.

What options do I have to correctly resolve my SIP client’s DNS requests correctly to the server assigned to my PPPoE connection?

  • Is it possible to redirect all DNS requests of a specific host (SIP client) to the dynamically assigned PPPoE Peer-DNS?


  • Is it possible to write a script which will run on each PPPoE update and assigns the PPPoE Peer-DNS IP address to a DstNAT rule to redirect my clients directly to the correct DNS server?


  • Is it possible to tell ROS to not buffer specific DNS entries and always request them from the upstream DNS server?


  • Is it possible to run the ROS DNS Server without any buffering (to ensure the provider will never change my server and having a delay (because of the DNS TTL) on my side until updating my clients)?

Or do you have any better ideas?

Thanks a lot in advance,

Thomas

2

hello.

Is it possible to redirect all DNS requests of a specific host (SIP client) to the dynamically assigned PPPoE Peer-DNS?

yes it is possible by using dst-nat. but the redirection results are depend on your isp pppoe routing scope and firewalls.

the results might be the same if you try to access your sip server from outside your isp network.

i think there’s no need to overwhelmed a simple redirection with script.

— edit. forgot about the dns buffering.

about the by passing certain dns query from your mikrotik dns caching servers,

you could just not using the mikrotik dns, and query directly to your isp.

don’t make your mikrotik router life harder by enabling that firewall content matcher.

have a good try, and good luck :+1:t2:

3

Okay, that’s clear.

How can I directly query to the DNS server of my ISP?
Especially, if I use the re-direct via DstNAT (as mentioned above), how can I specify the IP address of the dynamically assigned DNS server of the PPPoE connection to my ISP?

4

hi.

How can I directly query to the DNS server of my ISP?

dns server address is an option in every dhcp client setting. as well as the gateway address.

so, if you don’t want to query your mikrotik dns service, you can just use your own preferred isp dns setting on your sip client setting. but, the results will be applied to all dns query from that client.

if you want to use the firewall content matcher for specific dns query to your isp, mikrotik wiki has very good example of it.

basically, make an exemption src-addr list, proto tcp udp 53 to not use mikrotik dns.

— edit. ok. good point.

about changing the dns address for the dhcp client.

yes, that should be scripted.
to read from the pppoe dns, then distribute that dns address to dhcp scope option setting.

hope this helps.