OSPF - Autonomous System Boundary Router (ASBR)

OSPF - Type 5 LSA filtering on an ASBR

OSPF Forwarding Address

OSPF LSA Types


An [OSPF](/ospf) Type 5 [Link State Advertisement (LSA)](/ospf-lsa-types), also known as an External LSA, that contains information about routes that are external to the OSPF domain.  Such an LSA is generated by ASBRs and propagated from area to area by [ABR](/ospf-area-border-router-abr)s.

Take a look at this diagram:

![ospf-lsa-type-5.png](/attachments/ospf-lsa-type-5.png)

In the above diagram, you can see that R1 is an [ASBR](/ospf-autonomous-system-boundary-router-asbr) because it is connected to a [RIP](/rip) domain, which resides outside of the OSPF routing domain.  Information from that RIP domain is learned by R1 and is injected into OSPF Area 2 using a  Type 5 LSA.

This LSA is then propagated via ABRs from area to area.  In this case, R2 injects it into Area 0 and R3 injects it into Area 51.

In large networks, Type 5 LSAs can create very large Link State Databases (LSDBs).  For this reason, the idea of an [OSPF Stub area](/ospf-stub-areas-and-allowed-lsas) has been introduced that allows and disallows various types of LSAs.  In particular, stub areas will not allow External LSAs within that area.

For this reason, [OSPF NSSAs](/ospf-not-so-stubby-area-nssa) have been introduced along with [Type 7 LSAs](/ospf-type-7-lsa) to allow ASBRs to operate within a stub network.

## Links

https://networklessons.com/ospf/ospf-lsa-types-explained

https://networklessons.com/ospf/how-to-configure-ospf-stub-area



OSPF Type 5 LSA

OSPF - Type1 LSA

OSPF - Update pacing timers

OSPF - capablity vrf-lite

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 - network type mismatch

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

OSPF BDR to DR Transition Time

OSPF DR BDR election and neighbor adjacencies

OSPF DR BDR election criteria

OSPF DR BDR election process

OSPF Database Exchange Process Master Slave Election

OSPF Design - When to create new instance

OSPF Determining which LSA is newer

OSPF Discontiguous Area 0

OSPF Do Not Age (DNA) Flag

OSPF E1 E2 N1 N2 routes

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 NSSA ABR advertises default route

OSPF Not So Stubby Area NSSA

OSPF Packet Types and Their Transmission Methods

OSPF Path selection

OSPF Prefix Suppression Considerations

OSPF Route Filtering

OSPF Routing Bit

OSPF SPF Scheduling and throttling timers

OSPF Summarization Restrictions Within an Area

OSPF TTL Security Check

OSPF Troubleshooting

OSPF Type 3 LSA

OSPF Type 4 LSA

OSPF Type 7 LSA

OSPF Understanding LSA Aging and Refreshing

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 duplicate router IDs

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 packet types

OSPF point to point network type for Ethernet

OSPF requirements for forming adjacency

OSPF router ID in an IPv6 environment

OSPF router ID

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

OSPF

OSPFv2 and OSPFv3 comparison

OSPFv3 - router ospfv3 command

OSPFv3 communication between routers and next hop addresses

OSPFv3 instance ID

Offset-list

PAT (overloading) maximum number of translations per inside global address

PAgP

PBR - Policy Based Routing

PBR - Transport Layer port number

PBR - load balancing

PBR - matching prefix lists

PBR - route-map and ACL deny statements not supported

PBR - set interface command

PBR next hop recursive

PBR next hop verify availability

OSPF Type 5 LSA

Links

Links to this page: