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1 Eigrp Packet Header

EIGRP Packet Header

RFC 7868: Section 6.5

The EIGRP packet header provides essential information about an Enhanced Interior Gateway Routing Protocol (EIGRP) packet. It includes the following fields:

  • Version: The version of EIGRP in use. Version 2 is the current and widely adopted version.

  • Opcode: This field indicates the purpose or type of the EIGRP packet. Possible opcode values include:

    • Update (1): Used for sending routing updates.
    • Request (2): Sent to request specific information from a neighbor.
    • Query (3): Used to query neighbors for specific route information.
    • Reply (4): Sent as a response to a query packet.
    • Hello (5): Used for neighbor discovery and maintenance.
    • SIA-Query (10): Used to query for Stuck-in-Active (SIA) routes.
    • SIA-Reply (11): Sent in response to SIA queries.

  • Checksum: A field used for error checking and ensuring the integrity of the packet.

  • Flags: Various flags that may be set in the EIGRP packet header, including:

    • Init: Indicates the start of an EIGRP session.
    • Conditional Receive (CR): Used for advanced protocol features.
    • Restart: Indicates a restart of the EIGRP process.
    • End of Table (EOT): Marks the end of a table in a packet.

  • Sequence Number: A unique number assigned to each EIGRP packet. It helps in ordering and sequencing packets.

  • Acknowledgement Number: Indicates the acknowledgment number for the received packet.

  • Virtual Router ID: Identifies the virtual router within the EIGRP domain. Multiple virtual routers can exist within the same EIGRP autonomous system (AS).

  • Autonomous System (AS) Number: The AS number associated with the EIGRP routing domain.

In summary, the EIGRP packet header contains vital information necessary for EIGRP routing, including version, opcode, checksum, flags, sequence numbers, acknowledgment numbers, virtual router IDs, and AS numbers.

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