EIGRP - Routing Protocols and Concepts - page 397

Convergence

Because of the unreliable nature of periodic updates, traditional distance vector routing protocols are
prone to routing loops and the count-to- infinity problem. RIP and IGRP use several mechanisms to
help avoid these problems including hold-down timers, which cause long convergence times.

EIGRP does not use hold-down timers. Instead, loop-free paths are achieved through a system of route
calculations (diffusing computations) that result is faster convergence than traditional distance vector
routing protocols.

EIGRP Message Format

Figure 9-1 shows an example of an encapsulated EIGRP message. Fill in the missing field contents.

Figure 9-1 Encapsulated EIGRP Message (Answer)

Data Link Frame
Header

IP Packet
Header

EIGRP Packet
Header

Type/Length/Values Types

Data Link Frame
MAC Source Address = Address of Sending Interface
MAC Destination Address = Multicast: 01-00-5E-00-00-0A
IP Packet
IP Source Address = Address of Sending Interface
IP Destination Address = Multicast:
Protocol Field = for EIGRP
EIGRP Packet Header
Opcode for EIGRP Packet Type

224.0.0.10

88

AS Number

TLV Types
Some Types Include:
0x0001
0x0102
0x0103

EIGRP Parameters
IP Internal Routes
IP External Routes

The EIGRP packet header is included with every EIGRP packet, regardless of its type. In the IP pack-
et header, the protocol field is set to 88 to indicate EIGRP, and the destination address is set to the
multicast 224.0.0.10 .

Every EIGRP message includes the header, as shown in Figure 9-2. Fill in the missing field contents.

Figure 9-2 EIGRP Packet Header (Answer)

Data Link Frame
Header

IP Packet
Header

EIGRP Packet
Header

Type/Length/Values Types

Bit 0 7 8 15 16 23 24 31

Version Opcode Checksum

Flags
Sequence
Ack

EIGRP
Header

Autonomous System

EIGRP
Message

Numbers TLVs