Information About The Service Discovery Gateway And Mdns; Mdns; Mdns-Sd - Cisco Catalyst 3850 series Configuration Manual

Information about the Service Discovery Gateway and mDNS

• The Service Discovery Gateway does not support topologies with multiple hops. All network segments

Information about the Service Discovery Gateway and mDNS

mDNS

mDNS was defined to achieve zero configuration, with zero configuration being defined as providing the
following features:
• Addressing—Allocating IP addresses to hosts
• Naming—Using names to refer to hosts instead of IP addresses
• Service discovery—Finding services automatically on the network
With mDNS, network users no longer have to assign IP addresses, assign host names, or type in names to
access services on the network. Users only need to ask to see what network services are available, and choose
from a list.
With mDNS, addressing is accomplished through the use of DHCP/DHCPv6 or IPv4 and IPv6 Link Local
scoped addresses. The benefit of zero-configuration occurs when no infrastructure services such as DHCP or
DNS are present and self-assigned link-local addressing can be used. The client can then select a random IPv4
address in the link-local range (169.254.0.0/24) or use its IPv6 link-local address (FE80::/10) for communication.
With mDNS, naming (name-to-address translation on a local network using mDNS) queries are sent over the
local network using link-local scoped IP multicast. Because these DNS queries are sent to a multicast address
(IPv4 address 224.0.0.251 or IPv6 address FF02::FB), no single DNS server with global knowledge is required
to answer the queries. When a service or device sees a query for any service it is aware of, it provides a DNS
response with the information from its cache.
With mDNS, service discovery is accomplished by browsing. An mDNS query is sent out for a given service
type and domain, and any device that is aware of matching services replies with service information. The
result is a list of available services for the user to choose from.
The mDNS protocol (mDNS-RFC), together with DNS Service Discovery (DNS-SD-RFC) achieves the
zero-configuration addressing, naming, and service discovery.

mDNS-SD

Multicast DNS Service Discovery (mDNS-SD) uses DNS protocol semantics and multicast over well-known
multicast addresses to achieve zero configuration service discovery. DNS packets are sent to and received on
port 5353 using a multicast address of 224.0.0.251 and its IPv6 equivalent FF02::FB.
Because mDNS uses a link-local multicast address, its scope is limited to a single physical or logical LAN.
If the networking reach needs to be extended to a distributed campus or to a wide-area environment consisting
of many different networking technologies, mDNS gateway is implemented. An mDNS gateway provides a
transport for mDNS packets across Layer 3 boundaries by filtering, caching, and redistributing services from
one Layer 3 domain to another.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
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must be connected directly to it. The Service Discovery Gateway can learn services from all connected
segments to build its cache and respond to requests acting as a proxy.
Configuring the Service Discovery Gateway
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