
Within the context of an [OSPF](/ospf) topology, the E-bit, also called the [ASBR](/ospf-autonomous-system-boundary-router-asbr) bit, is a flag found within a [Type 1 LSA](/ospf-type-1-lsa) that indicates that the sending router is an ASBR.  It is used to signal to its neighbors that it is capable of reaching networks that are external to the OSPF domain.

When an ASBR sends such a Type 1 LSA< the receiving ABR will relay that information to the rest of the OSPF domain as a [Type 4 Summary LSA](/ospf-type-4-lsa), as shown in the following diagram:

![ospf-lsa-type-4-1024x372.png](/attachments/ospf-lsa-type-4-1024x372.png)

## Links

https://networklessons.com/ospf/ospf-lsa-types-explained
https://datatracker.ietf.org/doc/html/rfc2328#appendix-A.2

OSPF - ASBR E-bit in an LSA

NetFlow - Flexible NetFlow

NetFlow - Flow Samplers

NetFlow - applying to an SVI

NetFlow - what is a flow

NetFlow local cache size

NetFlow

Network - BUM Traffic

Network - Discontiguous or Discontinuous

Network - Discontiguous

Network - Example of communication, encapsulation, and decapsulation, between hosts

Network - Layer 3 network

Network - Monitoring multiple IPs of a single device with Observium

Network - Observium vs LibreNMS

Network - Simultaneous network traffic handling

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Network Address Translation (NAT)

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Network Design Achieving Redundancy with PE Devices

Network Design Considerations Involving PE and P Routers

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Nexus

OSI Model

OSPF - A comparison with IS-IS

OSPF - ABR has at least one interface in Area 0

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

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OSPF - DR-BDR election priority of zero

OSPF - Database Example

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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

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OSPF - Type 1 LSA

OSPF - Type 5 LSA filtering on an ASBR

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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 Authentication for v2 and v3