etwork. For example, all EIGRP routers within the same domain must be able to communi- cate with each other. Defining specific neighbors is not necessary with this protocol because they are discovered dynamically. Most interior gateway protocols discover neighbors dynamically. BGP does not discover neighbors. Instead, BGP must be configured to communicate with each neighbor manually. 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 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 configured to statically assign neighbors. This usually results in uni- cast messages being sent to specific routers instead of multicasts. Communication Between Routers 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 that are running the same routing protocols communicate with and discover each other. Router A Router B Router EIGRP Router D Router E Figure 10-1. Mu