ccna global knowledge

ccna global knowledge.Figure 16-1 EIGRP FSM Logic16.1.3 IPv4EIGRP Packet TypesThere are five IPv4EIGRP packet types, and certain types (such as query and reply) are used in pairs. IPv4EIGRP packets can be sent as unicast or multicast depending on the situation. Hello packets: sent periodically as multicast to establish and maintain EIGRP neighbor relationships. Hello numberThe acknowledgement number of the data packet is always 0 and therefore no acknowledgement is required. By default. an EIGRP Hello packet is sent every 5 seconds on a point-to-point link or a multipoint link with a bandwidth greater than T1. On low-speed links with bandwidths less than T1, EIGRP Hello packets are sent every 60 seconds. The hold time is the maximum time that an EIGRP neighbor receiving this packet should wait before it believes that the router sending the announcement is down. By default, the hold time is three times the interval between Hello packet transmissions. After the hold time is reached, EIGRP deletes the neighbor and all entries in the topology table learned from the neighbor.Update packets: When a router receives the first Hello packet from a neighboring router, the neighbor relationship is successfully negotiated and an update packet containing the routing information it knows is sent as a unicast transmission. When the routing information changes, an update packet containing only the changed routing information is sent as a multicast transmission. EIGRP uses partial updates and qualified updates in routing updates. A partial update is a routing update that contains only the information related to the routing change. A qualified update is one in which partial update information is sent only to the routers affected by the change. Qualified updates help EIGRP minimize the bandwidth required to send EIGRP update information. Update packets are delivered in a reliable manner and therefore require neighbors to send acknowledgement packets for confirmation.Query packet: When a link fails and there are no feasible successor routes in the topology table, the router needs to re-run the route computation, and the router sends a query packet as a multicast to its neighbors to ask if they have a route to the destination network. The query packet is usually a multicast packet.Reply packet: A unicast response to a neighbor's query, the reply packet is a unicast packet.Acknowledgement (ACK) packets: Hello packets sent unicast without any data, containing a non-zero acknowledgement number, are used to acknowledge update, query and reply packets. Acknowledgement packets do not require acknowledgement.16.1.4 IPv4EIGRP Packet FormatEach IPv4E1GRP packet consists of an EIGRP packet header and a T/L/V [Type /Length / Value]. The IPv4EIGRP packet header and TLV are encapsulated into an IP packet with a protocol field of 88, representing EIGRPo If the IPv4EIGRP packet is a multicast packet, the destination address is the multicast address 224.0.0.10, and if the EIGRP packet is encapsulated within an Ethernet frame, the multicast destination MAC address is 01 -00-5E-00-00-0Ao The IPv4EIGRP packet format is shown in Figure 16.2.