OSPF best way to learn
Here's a table showing the step-by-step process of forming an OSPF adjacency between two routers, R1 (10.1.1.1) and R2 (10.1.1.2), along with the messages exchanged at each step. This will help you understand what to expect in Wireshark packets.
| Step | State | Router 1 (R1) - 10.1.1.1 | Router 2 (R2) - 10.1.1.2 | Message Type | Description |
|---|---|---|---|---|---|
| 1 | Down | Sends Hello | Sends Hello | Hello | Initial Hello packets sent to discover neighbors. |
| 2 | Init | Receives Hello | Receives Hello | Hello | Hello packets received, but Router IDs not yet seen in each other's Hello. |
| 3 | 2-Way | Sees R2's Router ID in Hello | Sees R1's Router ID in Hello | Hello | Bidirectional communication established. |
| 4 | ExStart | Sends DBD (Master) | Sends DBD (Slave) | DBD (Database Description) | Master and slave roles determined, initial sequence number set. |
| 5 | Exchange | Sends DBD | Sends DBD | DBD | Exchange of Database Description packets to describe link-state databases. |
| 6 | Loading | Sends Link-State Request | Sends Link-State Request | Link-State Request | Requests for detailed information about routes described in DBD packets. |
| 7 | Loading | Sends Link-State Update | Sends Link-State Update | Link-State Update | Detailed route information sent in response to Link-State Requests. |
| 8 | Full | Database synchronized | Database synchronized | - | Routers have identical link-state databases, adjacency fully established. |
Wireshark Packet Details
Hello Packet:
- Fields: Router ID, Area ID, Hello Interval, Dead Interval, Neighbor IDs.
- Purpose: Discover and maintain neighbor relationships.
Database Description (DBD) Packet:
- Fields: Interface MTU, Options, Sequence Number, LSA Headers.
- Purpose: Summarize the contents of the link-state database.
Link-State Request Packet:
- Fields: LSA Type, Link-State ID, Advertising Router.
- Purpose: Request detailed information about specific LSAs.
Link-State Update Packet:
- Fields: LSA Type, Link-State ID, Advertising Router, LSA Data.
- Purpose: Provide detailed information about specific LSAs.
By capturing these packets in Wireshark, you can observe the OSPF neighbor state transitions and the exchange of routing information between R1 and R2
The master-slave relationship in OSPF is formed during the ExStart state of the neighbor adjacency process. The router with the higher Router ID becomes the master, and the other becomes the slave. This relationship is crucial for the exchange of Database Description (DBD) packets.
Criteria for Master-Slave Election
- Router ID: The router with the higher Router ID is elected as the master.
- Sequence Numbers: The master initiates the DBD packet exchange and controls the sequence numbers.
Real Configuration Example
Let's use the topology with two routers, R1 (10.1.1.1) and R2 (10.1.1.2). Here are the configurations and the steps involved:
Router R1 Configuration (10.1.1.1)
Router(config)# router ospf 1
Router(config-router)# router-id 1.1.1.1
Router(config-router)# network 10.1.1.0 0.0.0.255 area 0
Router R2 Configuration (10.1.1.2)
Router(config)# router ospf 1
Router(config-router)# router-id 2.2.2.2
Router(config-router)# network 10.1.1.0 0.0.0.255 area 0OSPFv2 and OSPFv3 are both versions of the OSPF routing protocol, but they have several key differences, primarily due to OSPFv3's support for IPv6. Here's a comparison of the two:
Key Differences Between OSPFv2 and OSPFv3
Feature OSPFv2 OSPFv3 Protocol Version OSPFv2 (RFC 2328) OSPFv3 (RFC 5340) IP Version IPv4 IPv6 Addressing Uses IPv4 addresses Uses IPv6 addresses, primarily link-local LSA Types Types 1-5 Types 1-5, plus new types 8 and 9 Authentication Built-in (MD5, plain text) Relies on IPsec for authentication Packet Format Includes IPv4 addresses Includes IPv6 addresses, no network mask field Instance ID Not used Used to support multiple OSPF instances on a link Link Handling Per subnet Per link Multicast Addresses 224.0.0.5 (All SPF Routers), 224.0.0.6 (All DR Routers) FF02::5 (All SPF Routers), FF02::6 (All DR Routers) LSA Flooding Scope Area, AS Link, Area, AS Router ID and Area ID 32-bit 32-bit Support for Multiple Instances No Yes
Detailed Differences
Addressing and IP Version:
- OSPFv2: Designed for IPv4 networks, uses IPv4 addresses.
- OSPFv3: Designed for IPv6 networks, uses IPv6 addresses, primarily link-local addresses for communication.
LSA Types:
- OSPFv2: Supports LSA Types 1-5.
- OSPFv3: Supports LSA Types 1-5, and introduces new LSA Types 8 (Link LSA) and 9 (Intra-Area Prefix LSA) to handle IPv6 prefixes.
Authentication:
- OSPFv2: Includes built-in authentication methods (MD5, plain text).
- OSPFv3: Relies on IPsec for authentication, providing more flexible and secure options.
Packet Format:
- OSPFv2: Includes IPv4 addresses and network mask fields.
- OSPFv3: Uses IPv6 addresses and does not include network mask fields, as IPv6 handles addressing differently.
Instance ID:
- OSPFv2: Does not use Instance IDs.
- OSPFv3: Uses Instance IDs to support multiple OSPF instances on a single link, allowing for more flexible network designs.
Link Handling:
- OSPFv2: Operates on a per-subnet basis.
- OSPFv3: Operates on a per-link basis, allowing multiple IP subnets on a single link.
Multicast Addresses:
- OSPFv2: Uses 224.0.0.5 for All SPF Routers and 224.0.0.6 for All DR Routers.
- OSPFv3: Uses FF02::5 for All SPF Routers and FF02::6 for All DR Routers.
Summary
OSPFv3 is an adaptation of OSPFv2 to support IPv6, with changes in addressing, LSA types, authentication, and packet formats. These differences allow OSPFv3 to efficiently handle the requirements of IPv6 networks while maintaining the core functionalities of OSPF
Comments
Post a Comment