1. Teemu Savolainen (Nokia) MIF WG meeting @ IETF#75 28-July-2009
DNS Server Selection on Multi-Homed Hosts draft-savolainen-mif-dns-server-selection-00
Teemu Savolainen (Nokia)
MIF WG IETF#75
28-July-2009

2. Split-DNS
Host receives recursive DNS server addresses from multiple network interfaces, but some of the DNS servers may serve information others do not
(Primary/secondary servers from an interface are assumed to serve same information)
Some have unique information not available on others
E.g. IP addresses for private FQDNs
Some serve different information for the same query
E.g. FQDN results in different IP addresses from different interface’s name servers, and even worse, same FQDN may result in IP addresses of completely different network entities/services

3. What a MIF host should be able to accomplish
Send queries to DNS server able to answer properly
Use resolved IP addresses on the interface they work on

4. But there are problems.. How to select right DNS server?
Source/destination address selection algorithms are not suitable, as no destination IP addresses are available
“Second interface’s” DNS server might be able to serve even if “first interface’s” DNS server returned negative reply

5. Solution approaches
Avoid setting-up split-DNS => avoid creation of the problem
Bind applications to specific interfaces
See draft-mrw-mif-current-practices – i.e. even if host is multi-interfaced, an application would not be
Come up with optimized DNS resolution algorithm

6. Possibilities for the algorithm
Loop through DNS servers of all interfaces, collect responses, and prioritize conflicting information
May require waking up radio (battery consumption)
Increases number of DNS queries (increased traffic)
Increase odds by selecting the DNS server based on DNS suffixes (draft-savolainen-mif-dns-server-selection)
Learn interface specific DNS suffixes dynamically
E.g. DHCP Domain Search List option 119 (RFC3397)
E.g. DHCPv6 Domain Search List option 24 (RFC3646)
Send queries over an interface with matching suffix
Create interface specific DNS cache or have interface information in DNS cache
Otherwise problems may arise after movement

7. Comments and next steps
Yes, MIF is chartered to work on problem statement, existing practices, and analysis…
How many people are interested on this problem?