OSPF
Open Shortest Path First (OSPF) is a link state routing protocol that was developed for IPv4 and later IPv6 networks and is based on the Shortest Path First (SPF) algorithm. OSPF is an Interior Gateway Protocol (IGP).
OSPF Version 2 is defined in RFC 2328 for IPv4.
The updates for IPv6 are specified as OSPF Version 3 in RFC 5340.
For our entire OSPF course, take a look here:
https://networklessons.com/ospf
Basics
- OSPF packet types
- OSPF Path selection
- OSPF router ID
- OSPF Why it is not suitable for use on the Internet
- OSPF loop prevention
- OSPF - Area Border Router (ABR)
- OSPF ABR and Loop Prevention
- OSPF - ABR has at least one interface in Area 0
Neighbor Adjacency
Before OSPF routers can exchange LSAs, we have to form a neighbor adjacency.
- OSPF requirements for forming adjacency
- OSPF DR BDR election and neighbor adjacencies
- OSPF DR BDR election criteria
- OSPF DR BDR election process
- OSPF duplicate router IDs
- OSPF Hello packets unicast and multicast
- OSPF immediate hello packet
- OSPF Database Exchange Process Master Slave Election
- OSPF network types
Advertise
Notes related to how OSPF can advertise network information.
LSAs
OSPF uses Link State Advertisements (LSA) to advertise routing information.
- OSPF ABR Type 3 LSA filtering using access lists
- OSPF Determining which LSA is newer
- OSPF LSA Recursion
- OSPF LSA Sequence Numbers
- OSPF LSA Types
- OSPF Type 4 LSA
- OSPF Incremental SPF and receipt of LSAs
Areas
Everything related to OSPF areas.
- OSPF backbone area 0
- OSPF why is a backbone area 0 necessary
- OSPF Stub areas allowed LSAs
- OSPF area inactive
- OSPF area notation
- OSPF area type mismatch
- OSPF Discontiguous Area 0
- OSPF within what area is an OSPF router considered to be
- OSPF NSSA ABR advertises default route
Security
Notes related to making OSPF more secure.
IPv6
OSPFv2 is for IPv4. OSPFv3 supports both IPv4 and IPv6.
- OSPFv2 and OSPFv3 comparison
- OSPFv3 communication between routers and next hop addresses
- OSPFv3 instance ID
- OSPF router ID in an IPv6 environment
Advanced Features
Advanced features of OSPF that don't belong to any of the other topics.
- LFA, remote LFA, and how they work together in OSPF(
- OSPF sham-link
- OSPF sham-link cost
- VRF capability vrf-lite command
- Route-map matching OSPF router ID
- OSPF SPF Scheduling and throttling timers
Troubleshooting
How to troubleshoot OSPF when you can't form neighbor adjacencies or exchange routing information.
Misc
A collection of miscellaneous topics.
- OSPF IS-IS comparison
- OSPF in a GRE multipoint environment
- OSPF IP Unnumbered
- OSPF extent of reconvergence process
- OSPF Forwarding Address
- OSPF metric sum of outgoing interface costs
- OSPF Routing Bit
- OSPF where do you configure a virtual link
Links
https://www.ietf.org/rfc/rfc2328.txt https://datatracker.ietf.org/doc/html/rfc5340
Links to this page:
- home
- ACL Behavior with Local vs Transient Traffic
- ASBR Behavior with External Type 2 OSPF Routes
- BFD - Control Plane Independent (CPI) bit
- BFD - with multiple routing protocols
- BFD Session Troubleshooting
- BGP - bgp redistribute-internal command
- BGP - redistributing iBGP routes into an IGP
- BGP Path Selection Using IGP Metric as Tiebreaker
- BGP
- Career study advice
- Cisco IOS On Linux (IOL) Containers
- CoPP - Best practices and operation
- DMVPN - Dual-Hub Single-Cloud with redundant spoke links config guidelines
- DMVPN - OSPF and multiple areas
- DMVPN - Phase 2 BGP peerings
- DMVPN - Phase 2 EIGRP neighbor adjacencies
- DMVPN - Phase 2 OSPF neighbor adjacencies
- DMVPN - What is the best routing protocol to use
- DMVPN - using a default route
- DMVPN dual hub single cloud
- DMVPN
- Demand Circuits
- Distribute-lists - using route maps to set attributes
- EGP
- EIGRP - Advertised metric is cumulative
- EIGRP - Source of values for metric calculation
- EIGRP - internal vs external routes
- FHRP - interaction with routing protocols
- GRE - Recursive routing error
- IOS key chain feature
- IP Addressing on a Router
- IPv4 - header protocol field
- IPv4 point to point addresses
- IS-IS
- Interface speed and bandwidth
- Interior Gateway Protocol (IGP)
- LFA - Topology Independent LFA
- LFA, remote LFA, and how they work together in OSPF
- Link State Routing Protocols
- Loop-Free Alternate (LFA) Fast Reroute (FRR)
- Loop-Free Alternate (LFA) and remote LFA
- MPLS - L3VPN BGP OSPF Redistribution
- MPLS - OSPF redistributed routes appear as O IA
- MPLS - Using RSVP for Traffic Engineering
- MPLS - multiarea OSPF in the core
- MPLS Label Edge Router
- MPLS advertising multiple customer subnets
- MPLS-TE - why are IGPs necessary
- Multi-Topology Routing
- Multicast - Example Use Cases
- Multicast - Local Network Control Block
- Multicast - PIM
- Multicast local subnetwork address range
- Network - Discontiguous
- Network - control plane
- Network Design - Load Balancing vs Load Sharing
- Network Design Achieving Redundancy with PE Devices
- Network Flapping
- Networks - Underlay Network
- Next Hop
- OSPF - A comparison with IS-IS
- OSPF - ABR has at least one interface in Area 0
- OSPF - ASBR E-bit in an LSA
- OSPF - Adjacencies in a Multi-Access network segment
- OSPF - Adjacency Between NBMA and P2MP Non-Broadcast Networks
- OSPF - Advertising point to multipoint networks
- OSPF - Area Border Router (ABR)
- OSPF - Autonomous System Boundary Router (ASBR)
- OSPF - BDR is elected before DR
- OSPF - Cost of summarized routes
- OSPF - DR-BDR election per broadcast domain
- OSPF - DR-BDR election priority of zero
- OSPF - Database Example
- OSPF - Default route advertisement next hop IP
- OSPF - Down (DN) Bit
- OSPF - ECMP across two different areas
- OSPF - ECMP to destination in Area 0
- OSPF - Enabling authentication
- OSPF - HMAC-SHA Extended Authentication
- OSPF - Identifying the router type
- OSPF - LSA Max Age
- OSPF - LSA Refresh Time
- OSPF - LSA checksum
- OSPF - Link ID and ADV Router in the OSPF database
- OSPF - Link ID in the OSPF database
- OSPF - Link State Updates (LSUs)
- OSPF - MPLS SuperBackbone
- OSPF - NBMA neighbors listen on 224.0.0.5
- OSPF - NSSA P-bit
- OSPF - NSSA no automatic default route
- OSPF - Neighbor states
- OSPF - Neighbor vs Adjacency
- OSPF - OSPFv3 authentication
- OSPF - Propagation of routes between areas
- OSPF - Stuck in ATTEMPT neighbor state
- OSPF - Stuck in ExStart or Exchange states
- OSPF - Type 1 LSA
- OSPF - Type 5 LSA filtering on an ASBR
- OSPF - Update pacing timers
- OSPF - control plane vs data plane loops
- OSPF - default-information originate always command
- OSPF - distance command
- OSPF - distribute-list filtering
- OSPF - manual neighbor configuration
- OSPF - non-zero Forwarding Address example
- OSPF - point-to-multipoint network type
- OSPF - route summarization
- OSPF - summary-address nssa-only on an ABR
- OSPF - what triggers a DR-BDR election
- OSPF ABR Type 3 LSA filtering using access lists
- OSPF ABR and Loop Prevention
- OSPF Advertising Networks using Redistribution vs Network Commands
- OSPF Authentication for v2 and v3
- OSPF BDR to DR Transition Time
- OSPF DR BDR election and neighbor adjacencies
- OSPF DR BDR election criteria
- OSPF DR BDR election process
- OSPF Design - When to create new instance
- OSPF Determining which LSA is newer
- OSPF Discontiguous Area 0
- OSPF Do Not Age (DNA) Flag
- OSPF Forwarding Address
- OSPF Hello packets unicast and multicast
- OSPF IP Unnumbered
- OSPF IS-IS comparison
- OSPF Incremental SPF and receipt of LSAs
- OSPF LSA Persistence with DNA flag
- OSPF LSA Recursion
- OSPF LSA Sequence Numbers
- OSPF LSA Types
- OSPF NSSA ABR advertises default route
- OSPF NSSAs, Totally NSSAs and Default Routes
- OSPF Neighbor Adjacency works with Network Type Mismatch
- OSPF Network Type in VXLAN the Underlay
- OSPF Packet Types and Their Transmission Methods
- OSPF Path selection
- OSPF Prefix Suppression Considerations
- OSPF Route Filtering
- OSPF Route Preference Intra-Area vs Inter-Area
- OSPF Routing Bit
- OSPF SPF Scheduling and throttling timers
- OSPF Stub Area vs Totally Stub Area
- OSPF Stub areas allowed LSAs
- OSPF Summarization Restrictions Within an Area
- OSPF TTL Security Check
- OSPF Troubleshooting
- OSPF Type 10 LSA
- OSPF Type 3 LSA
- OSPF Type 4 LSA
- OSPF Type 5 LSA
- OSPF Type 7 LSA
- OSPF Understanding LSA Aging and Refreshing
- OSPF Virtual Link Network Type Considerations
- OSPF Why it is not suitable for use on the Internet
- OSPF advertising loopback network
- OSPF area inactive
- OSPF area notation
- OSPF area type mismatch
- OSPF backbone area 0
- OSPF default metric values
- OSPF design - when to create a new area
- OSPF does not redistribute default route
- OSPF downheap LSA
- OSPF extent of reconvergence process
- OSPF immediate hello packet
- OSPF in a GRE multipoint environment
- OSPF loop prevention
- OSPF message options field
- OSPF metric sum of outgoing interface costs
- OSPF modifying the router ID
- OSPF network command
- OSPF network types
- OSPF non directly connected neighbor adjacencies
- OSPF over VXLAN L2 VNI Considerations
- OSPF packet types
- OSPF point to point network type for Ethernet
- OSPF requirements for forming adjacency
- OSPF router ID in an IPv6 environment
- OSPF sham-link cost
- OSPF sham-link
- OSPF virtual link and ABRs
- OSPF where do you configure a virtual link
- OSPF why is a backbone area 0 necessary
- OSPF within what area is an OSPF router considered to be
- OSPFv2 and OSPFv3 comparison
- OSPFv3 - router ospfv3 command
- OSPFv3 Prefix Information Separation
- OSPFv3 communication between routers and next hop addresses
- OSPFv3 instance ID
- Passive interface
- Prefix Lists
- Protocols with LFA support
- QoS - Classification by IP
- QoS - effects of bandwidth interface command
- RIP
- Route-map matching OSPF router ID
- Routers - what is a loopback interface
- Routing - Difference between IGPs and EGPs
- Routing - Administrative Distance
- Routing - Classless and Classful routing protocols
- Routing - Dynamic routing protocols
- Routing - How the routing table is populated
- Routing - Link-State vs Distance-Vector routing protocols
- Routing - Link-state routing protocol use cases
- Routing - Using the Null0 interface to prevent routing loops
- Routing - address-family
- Routing - fully specified route
- Routing - ip default-network command
- Routing - link-local IPv6 next hop address needs exit interface
- Routing - network vs redistribute connected commands
- Routing - redistribute command
- Routing - route tagging
- Routing - seed metrics
- Routing - what is redistribution
- Routing NX-OS passive-interface default
- Routing Table
- Routing what if the administrative distance is the same
- Security and Routing Roles at the Network Edge
- Time to live
- Type Length Value (TLV)
- Upgrade your R&S skills to modern networking
- VRF capability vrf-lite command