ly. The Internet Assigned Numbers Authority (IANA) shows all multicast addresses in use at http://www.iana.org/assignments/multicast-addresses. Some of the more common multicast addresses include: 224.0.0.0 Base Address (Reserved) [RFC1112,JBP] 224.0.0.1 All Systems on this Subnet [RFC1112,JBP] 224.0.0.2 All Routers on this Subnet [JBP] 224.0.0.4 DVMRP Routers [RFC1075,JBP] 224.0.0.5 OSPFIGP OSPFIGP All Routers [RFC2328,JXM1] 224.0.0.6 OSPFIGP OSPFIGP Designated Routers [RFC2328,JXM1] 224.0.0.9 RIP2 Routers [RFC1723,GSM11] 224.0.0.10 IGRP Routers [Farinacci] 224.0.0.12 DHCP Server / Relay Agent [RFC1884] 224.0.0.18 VRRP [RFC3768] 224.0.0.102 HSRP [Wilson] The list shows that all IGRP (Internal Gateway Routing Protocol) routers, including Enhanced IGRP routers, will listen to packets sent to the address 224.0.0.10. Not all routing protocols use multicasts to communicate. Because BGP does not discover neighbors, it has no need for multicasts, and instead uses unicast packets. Many other routing protocols can also be config- ured to assign neighbors statically. This usually results in unicast mes- sages, instead of multicasts, being sent to specific routers. Chapter 10: Routing Protocols There may be more than one type of routing protocol on a single network. In the Ethernet network shown in Figure 10-1, for example, there are five routers, three of which are running OSPF, and two of which are running EIGRP. There is no reason for the EIGRP routers to receive OSPF updates, or vice versa. Using multicasts ensures that only the routers running the same routing protocols communicate with and discover each other. Router A Router B Router C EIGRP Router D Router E Figure 10-1. Multiple routing protocols on a single Ethernet network A network may also contain multiple instances of the same routing protocol. These separate areas of control are called autonomous systems in EIGRP, and domains in OSPF (although the term autonomous system is often used incorrectly). In EIGRP, each in- stance is referenced with an autonomous sy