Transcript DNS Server Selection on Multi-Homed Hosts

DNS Server Selection on
Multi-Homed Hosts
draft-savolainen-mif-dns-server-selection-00
Teemu Savolainen (Nokia)
MIF WG meeting @ IETF#75
28-July-2009
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Split-DNS
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Host receives recursive DNS server addresses from
multiple network interfaces, but some of the DNS servers
may serve information others do not
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Some have unique information not available on others
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(Primary/secondary servers from an interface are assumed to serve same information)
E.g. IP addresses for private FQDNs
Some serve different information for the same query
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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
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What a MIF host should be able to
accomplish
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Send queries to DNS server able to answer
properly
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Use resolved IP addresses on the interface they
work on
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But there are problems..
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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
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Solution approaches
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Avoid setting-up split-DNS => avoid creation of
the problem
Bind applications to specific interfaces
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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
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Possibilities for the algorithm
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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
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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
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Comments and next steps
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Yes, MIF is chartered to work on problem
statement, existing practices, and analysis…
How many people are interested on this
problem?
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