Scaling up DNS-based service discovery Go to ‘View’ menu > ‘Header and Footer…’ to edit the footers on this slide (click ‘Apply’ to change only the currently selected slide, or ‘Apply to All’ to change the footers on all slides). To add a background image to this slide; drag a picture to the placeholder or click the icon in the centre of the placeholder to browse for and add another image. Once added, the image can be cropped, resized or repositioned to suit. Scaling up DNS-based service discovery 18/09/2018 Dr Tim Chown, Jisc TNC, Prague, 15th June 2016

What is DNS-based service discovery? DNS-based service discovery (RFC 6763) was designed for zero configuration networking within a local subnet Allows devices to automatically discover services on other devices that are ‘nearby’ Driven by Apple, commonly referred to as ‘Bonjour’ Works with link-local addressing and naming (mDNS, under .local, as per RFC 6762), and DNS TXT/PTR/SRV records to describe the services Service discovery messages are sent as link scope multicast using well-known addresses, on UDP port 5353 IPv4 : 224.0.0.251 IPv6 : ff02::fb May be user to device, or device to device, with an ever wider variety of services for which discovery is desirable 15/06/2016 Scaling up DNS-based service discovery

OK, so what is the problem? The messages are constrained to a local subnet Because link scope multicast is not forwarded by routers So discovery only works for devices on the same link But increasingly they are not, e.g., devices in a campus network, or emerging multi-link home networks A screen in the same room, but on a wired network while you are on WiFi Two WiFi devices in different eduroam subnets Frustrating when you can see the device you want to discover! So how do we solve this? 15/06/2016 Scaling up DNS-based service discovery

Requirements? We’d like a scalable DNS-based service discovery mechanism Capable of running over / spanning multiple subnets Applicable to personal, home, campus, enterprise and other network scenarios Backwardly compatible with mDNS/DNS-SD And supporting incremental deployment May need to be be zero configuration, e.g., in the home Or may benefit from supporting administrator configuration, e.g., in a campus environment The IETF dnssd WG has been formed to address this problem, and it has already documented requirements Published as RFC 7558 – https://tools.ietf.org/html/rfc7558 15/06/2016 Scaling up DNS-based service discovery

What about solution approaches? What could we do? Define a new “xmDNS” that operates by extending mDNS to use site scope multicast messages Not scalable, or interoperable with existing mDNS Bridge queries and responses Beware loops. And no use when subnets are disjoint Make the network flat But a campus may have 20,000++ devices… Hybrid Unicast/Multicast DNS-Based Service Discovery Leaf routers act as proxies to their local links Clients query a list of proxies, and aggregate the results mDNS / DNS-SD runs as normal in local subnets 15/06/2016 Scaling up DNS-based service discovery

How far has the dnssd WG got? Produced a draft documenting the hybrid proxy solution https://tools.ietf.org/html/draft-ietf-dnssd-hybrid-03 Produced a draft on DNS Push mechanism Subscription-based DNS updates (for timeliness…) https://tools.ietf.org/html/draft-ietf-dnssd-push-07 Identified issues with label interoperability between mDNS and DNS name space (UTF-8 vs IDNA2008) https://tools.ietf.org/html/draft-ietf-dnssd-mdns-dns- interop-02 Considering privacy issues https://tools.ietf.org/html/draft-huitema-dnssd-privacy-01 Still non-standards work to be done as well… What does the user interface look like? 15/06/2016 Scaling up DNS-based service discovery

How you can get involved… Take a look at the IETF dnssd WG Charter: http://datatracker.ietf.org/wg/dnssd/charter/ Check the status pages for existing dnssd drafts: http://tools.ietf.org/wg/dnssd/ Join the mail list, join discussions: dnssd@ietf.org To join: https://www.ietf.org/mailman/listinfo/dnssd Explore early implementations See section 6 of the hybrid proxy draft 15/06/2016 Scaling up DNS-based service discovery

Find out more… Contact: Dr Tim Chown Senior Network Services Developer Tim.Chown@jisc.ac.uk jisc.ac.uk Go to ‘View’ menu > ‘Header and Footer…’ to edit the footers on this slide (click ‘Apply’ to change only the currently selected slide, or ‘Apply to All’ to change the footers on all slides). Except where otherwise noted, this work is licensed under CC-BY-NC-ND 15/06/2016 Scaling up DNS-based service discovery