EIGRP Packet Format

Figure 6-4 shows the EIGRP packet header. Notice that following the autonomous systems number are the Type/Length/Value (TLV) triplets. The TLV triplets carry route entries, as well as provide the fields for DUAL process management. Some common TLVs are the EIGRP parameter TLV, the IP internal route TLV, and the IP external route TLV.

Figure 6-4. EIGRP Packet Header

Figure 6-4. EIGRP Packet Header

The EIGRP packet parameters are described as follows:

• Version— Specifies different versions of EIGRP. Version 2 of EIGRP was imple-mented beginning with Cisco IOS Software Releases 10.3(11), 11.0(8), and 11.1(3). EIGRP Version 2 is the most recent version that contains many enhancements to improve the stability and scalability of EIGRP.

• Opcode— Specifies the types of EIGRP packet contained. Opcode 1 is the update packet, opcode 3 is the Query, opcode 4 is the reply, and opcode 5 is the EIGRP hello packet.

• Checksum— Used as the regular IP checksum, calculated based on the entire EIGRP packet, excluding the IP header.

• Flags— Involves only two flags now. The flag indicates either an init for new neighbor relationship or the conditional receive for EIGRP RTP.

• Sequence— Specifies the sequence number used by the EIGRP RTP.

• Acknowledgment— Used to acknowledge the receipt of an EIGRP reliable packet.

• Autonomous System Number— Specifies the number for the identification of EIGRP

network range.

One of the most common EIGRP TLVs is the EIGRP parameter TLV, as shown in Figure 6-5, which contains the parameter needed to establish a neighbor relationship. The constant K values are included in this TLV, as well as the hold time. The K values between two routers must agree before they can establish a neighbor relationship.

Figure 6-5. EIGRP Parameters TLV

Was this article helpful?

0 0

Post a comment