What is Multicast DNS?

 Multicast DNS (mDNS)

With regard to computer networking, mDNS (multicast DNS) is a protocol that resolves hostnames to IP addresses within small networks where a local nameserver is not included. It is a zero-configuration service. The multicast process is part of TCP/IP. It can work without the appropriate configurations.

Multicast DNS uses the same packet formats, operating semantics and programming interfaces as the unicast Domain Name System (DNS). Despite being designed as a stand-alone protocol, mDNS can work together with standard DNS servers. This protocol is published as RFC 6762. It uses IP multicast User Datagram Protocol (UDP) packets.

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How does Multicast DNS work?

Multicast DNS (mDNS) is a protocol that aids in name resolution in smaller networks. It makes use of a different approach than that in DNS, for the above-mentioned purpose. Rather than querying a nameserver, all participants in the network are directly addressed in it. A multicast is sent into the network by the appropriate client, while it is enquired about the network participant that matches up with the hostname. A multicast entails a unique type of communication. Through this unique form of communication an individual message is directed towards a recipients’ group, which can consist of an entire network or a sub-network. In this manner, the request also reaches that particular group participant by whom that hostname is owned that has been searched for. A response is generated for the entire network through the multicast. All participants receive information regarding the connection between the name and IP address. This enables them to make a corresponding entry into their multicast DNS cache. Till the time that this notation remains valid, none in the network requires to request the hostname.

A relatively large amount of traffic is created by the multicast DNS. It tries to save those network resources that are active. In order to accomplish this purpose, the client that has made the request sends a reply which as per the client is correct. In the event that this isn’t correct anymore or when the entry is going to expire, the recipient needs to reply. The other participants get informed prior to receiving a reply. Hence, this protocol reduces the traffic within the network. Only those hostnames are possible with multicast DNS that have the ending “.local”. This imposes a limitation on this type of name resolution on local networks. Multicast DNS does not process hostnames with other top-level domains (TLDs). Hence, this way can’t be used to resolve web addresses.

 

Advantages of Multicast DNS

There are many advantages of multicast DNS protocol. These are mentioned below, in no particular order.

It executes operation that is like DNS on local link, sans the conventional DNS server.

The mDNS system doesn’t require configuration or administration.

Multicast DNS service implementation does not need any additional infrastructure.

It works even when the system’s infrastructure fails.

It saves the cost that is required to reserve global domain name.

It doesn’t need a separate error detection mechanism.

It is designed for small networks and increases their user-friendliness.

It doesn’t need a server or directory to be established.

Additional devices can be imported quickly and dynamically.

Disadvantages of Multicast DNS

The disadvantages of multicast DNS are recounted below, in no particular order.

It can’t be used with regard to a network that has a large number of nodes.

Multicast DNS’ performance is poor compared to that of conventional DNS in network with larger nodes.

A large number of queries and their responses are generated by mDNS, which results in a significant burden on the local network.

Multiple IP subnets cannot use multicast DNS.

Multicast DNS burdens the processing power.

Confidential data can be found via an open multicast DNS.

Cybercriminals can find and use an open multicast DNS for DDoS (distributed denial-of-service) attacks.

Source: https://htswebhosting.wordpress.com/2021/01/27/what-is-multicast-dns/