Editing ICMP Router Discovery Protocol (section)

== Router discovery messages ==

To enable router discovery, the IRDP defines two kinds of ICMP messages:<ref name="Carrell">{{cite book|last1=Carrell|first1=Jeffrey L.|last2=Chappell|first2=Laura|last3=Tittel|first3=Ed|last4=Pyles|first4=James|title=Guide to TCP/IP|date=2013|publisher=Cengage Learning|isbn=978-1133019862|pages=288–289|url=https://books.google.com/books?id=mFr7CAAAQBAJ&q=%22Router+Discovery%22&pg=PA299|accessdate=23 June 2016|language=en}}</ref><ref name="Chen">{{cite book|last1=Chen|first1=Jyh-Cheng|last2=Zhang|first2=Tao|title=IP-Based Next-Generation Wireless Networks: Systems, Architectures, and Protocols|date=17 February 2004|publisher=John Wiley & Sons|isbn=9780471478263|page=182|url=https://books.google.com/books?id=2kSjPFW4tqEC&q=%22Router+Discovery%22&pg=PA182|accessdate=23 June 2016|language=en}}</ref>

* The ICMP Router Solicitation message is sent from a computer host to any routers on the local area network to request that they advertise their presence on the network.
* The ICMP Router Advertisement message is sent by a router on the local area network to announce its IP address as available for routing.

When a host boots up, it sends solicitation messages to IP multicast address 224.0.0.2.<ref name="Carrell" /> In response, one or more routers may send advertisement messages. If there is more than one router, the host usually picks the first message it gets and adds that router to its [[routing table]]. Independently of a solicitation, a router may periodically send out advertisement messages.<ref name="Panwar">{{cite book|last1=Panwar|first1=Shivendra S.|title=TCP/IP Essentials: A Lab-Based Approach|date=2004|publisher=Cambridge University Press|isbn=9780521601245|page=81|url=https://books.google.com/books?id=NbYKmCfw_PsC&q=%22ICMP+Router+Discovery%22&pg=PA81|language=en}}</ref> These messages are not considered a routing protocol, as they do not determine a routing path, just the presence of possible gateways.<ref name="Javvin" />