Dave Thaler Microsoft

Transcription

1 Dave Thaler Microsoft 1

2 Overview of design team recommendation Transport Mechanism: Q: How do discovery messages get from devices to servers (if any)? A: Site-scoped anycast Content Mechanism Q: What s the format of the discovery messages? A: DNS SRV lookups 2

3 Anycast deployment scenarios How do you securely inject anycast host route? Run DNS servers on routers Run routing daemons on DNS servers to talk to routers Run multiple servers on same link, configure servers routers with static route Upgrade servers routers to advertise route based on ND responses for anycast address Develop a real host-router anycast group joining protocol (draft-haberman-ipngwghost-anycast-00.txt) 3

4 Response must be able to contain: 1 or more DNS server addresses (ordered?) Could just be the anycast address Multiple addresses allow end nodes to more quickly fail over to other servers Client s domain name Client s search path (ordered) Response must fit in 512 bytes 4

5 Allow single config for entire site Allow per-subnet config as an option Request should include subnet information Want a single request message Implies a single query in practice 5

6 Anycast for name resolution DNS server list MAY just contain the anycast address itself Nodes just send UDP queries to the DNS server anycast address to resolve names Deployment notes: Already tried (w/o domain name or search path) Trivial to obtain & maintain server list, but slower convergence time on server failure Reply doesn t come from request destination 6

7 Resolver does a lookup using a wellknown domain name and service name IPNG WG will define details of how to embed necessary information in SRV records Mechanism can be disabled using an existing flag in Router Advertisements that says to use DHCP for other configuration 7

8 Specified in RFC 2782 Record has format _Service._Proto.Name TTL Class SRV Priority Weight Port Target Query for: _Service._Proto.Name Example: _ldap._tcp.example.com Priority field imposes an ordering Weight field used for probabilistic load balancing within a priority Target is a name 8

9 $ORIGIN example.com.... ; foobar - use old-slow-box or new-fast-box if ; either is available, make three quarters of the ; logins go to new-fast-box. _foobar._tcp SRV old-slow-box.example.com. SRV new-fast-box.example.com. ; if neither old-slow-box or new-fast-box is up, ; switch to using the sysdmin's box and the server SRV sysadmins-box.example.com. SRV server.example.com. ; NO other services are supported *._tcp SRV *._udp SRV

10 What name do you ask for? How do you do longest match, so that you get subnet-specific information if available, and site information otherwise? How encode 3 types of information? 10

11 Well known (domain) Name (local.arpa?) Well known Protocol: e.g. _dnsinfo Don t need to use this field for anything else Allows use of Service field for longest match wildcarding Put SLA in Service field of query Example: Client is on subnet fec0:0:1234::/64 Query for _1234._dnsinfo.local.arpa 11

12 Use Port to encode type (e.g., 0=domain name, 1=search path, 2=server) Use Priority to specify ordering within a type Only server Targets need address records 12

13 $ORIGIN local.arpa.... ; Specify default domain name *._dnsinfo SRV seattle.example.com. ; Specify default search path *._dnsinfo SRV seattle.example.com. *._dnsinfo SRV example.com. *._dnsinfo SRV foobar.com. ; Specify server list. Split among dns1-3 if ; available, else fall back to dns.foobar.com. *._dnsinfo SRV dns1.example.com. *._dnsinfo SRV dns2.example.com. *._dnsinfo SRV dns3.example.com. *._dnsinfo SRV dns.foobar.com. 13

14 ; Specify default domain name _1234._dnsinfo SRV marketing.example.com. ; Specify default search path _1234._dnsinfo SRV seattle.example.com. _1234._dnsinfo SRV example.com. ; Specify server list. Split among dns1-3. _1234._dnsinfo SRV dns1.example.com. _1234._dnsinfo SRV dns2.example.com. _1234._dnsinfo SRV dns3.example.com. 14

15 Can encode multiple types of information Can support 2-level longest match Site-specific and subnet-specific No changes to existing DNS servers 15

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