Fully Qualified Domain Name

I came across the term FQDN. It is also called as the absolute domain name.

Given a device with a local hostname 'myhost' and a parent domain name 'example.com', the fully qualified domain name is written like this:
myhost.example.com
The FQDN therefore uniquely identifies the device, while there may be many hosts in the world called myhost, there can only be one myhost.example.com.

Reference -> http://en.wikipedia.org/wiki/Fully_qualified_domain_name

DNS Server and DNS Resolver

DNS Server is looked into for resolving the DNS and the IP address and to forward the message to the particular DNS. In short, the DNS server acts as a database having the IP address and the Domain Names.

DNS client side is called as DNS resolver that is responsible for initating and sequencing the query so that the Domain Name gets mapped with the corresponding IP address. A DNS query may be either a non-recursive query or a recursive query.

Router Discovery Messages

The router discovery messages enable hosts to discover the existence of neighboring routers, but not which router is best to reach a particular destination. If a host chooses a poor first-hop router for a particular destination, it should receive an ICMP Redirect from that router, identifying a better one. These messages do not constitute a routing protocol.