Final answer:
The DNS record that specifies a host and port for discovering network services is the SRV (Server Record). It allows the identification of specific services by hostname and port number, compared to NS, PTR, and DKIM which serve different purposes.
Step-by-step explanation:
The DNS record that specifies a host and port information to help find specific services on a network is the SRV (Server Record). The SRV record essentially allows service discovery on a network by specifying the hostname and port number of servers offering particular types of services. For example, the SRV record is used in the context of SIP (Session Initiation Protocol) to locate SIP servers or in LDAP (Lightweight Directory Access Protocol) to find directory servers. This contrasts with other types of DNS records, such as NS (Network Service) records that delegate a DNS zone to use another name server, PTR (Pointer Record) that maps an IP address to a canonical host name, or DKIM records (DomainKeys Identified Mail) that are used to authenticate email messages.