OSPF - Cost of summarized routes

OSPF - route filtering

OSPF extent of reconvergence process

Summarization


[OSPF](/ospf) can do summarization, but it’s **impossible to summarize within an [area](/ospf-within-what-area-is-an-ospf-router-considered-to-be)**. This means we have to configure summarization on an **ABR or ASBR.** OSPF can **only summarize our [types 3 and 5](/ospf-lsa-types)**.

Summarization is applied using the `range` keyword under the OSPF configuration.  For example:

```
router ospf 1 
area 1 range 10.2.0.0 255.255.0.0
```

The `area range` command can only be applied at an ABR and it is used to perform route summarization. In the above example, it takes all learned prefixes from within area 1 that fall within the 10.2.0.0/16 range, and summarizes them before advertising them to other areas. This way you can consolidate multiple OSPF LSAs into a single summarized LSA making OSPF more efficient. 

The reason for this is that as a link-state protocol, every router within the same area must by definition have an identical link-state database (LSDB) for shortest path first (SPF) calculations. If you filter LSAs within an area, it would break this uniformity.

Similarly [route filtering in OSPF](/ospf-route-filtering) can only take place at an ABR.

For information about the cost used by OSPF in summarized routes, take a look at the [OSPF - Cost of summarized routes](/ospf-cost-of-summarized-routes) note.

Links:

https://forum.networklessons.com/t/introduction-to-ospf/878/191?u=lagapides

https://networklessons.com/ospf/how-to-configure-ospf-summarization

OSPF - route summarization

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

Network - Flapping

Network - Layer 2 network

Network - Layer 3 network

Network - Monitoring multiple IPs of a single device with Observium

Network - Observium vs LibreNMS

Network - broadcast domain

Network - control plane

Network - data plane

Network Address Translation (NAT)

Network Collisions

Network Design - Spine and leaf architecture

Network Design - Switch oversubscription ratios

Network Design - Traffic Engineering

Network Design - on-premises and off-premises

Network Time Protocol (NTP)

Network design - confine VLANs to as few access switches as possible

Network planes

Networking - what is a socket

Networks - Overlay Network

Networks - Overlay Transport Virtualization (OTV)

Networks - Spanning Layer 2 networks across remote sites

Networks - Underlay Network

Next Generation Multicast Virtual Private Network (NG-MVPN)

Nexus - using vPC with HSRP

Nexus - what is vPC

Nexus lacp rate fast

Nexus

OSI Model

OSPF - Advertising point to multipoint networks

OSPF - DR-BDR election per broadcast domain

OSPF - DR-BDR election priority of zero

OSPF - ECMP across two different areas

OSPF - Enabling authentication

OSPF - HMAC-SHA Extended Authentication

OSPF - Link State Updates (LSUs)

OSPF - MPLS SuperBackbone

OSPF - NBMA neighbors listen on 224.0.0.5

OSPF - NSSA P-bit

OSPF - Propagation of routes between areas

OSPF - Stub areas and allowed LSAs

OSPF - Type1 LSA

OSPF - Update pacing timers

OSPF - default-information originate always command

OSPF - distribute-list filtering

OSPF - manual neighbor configuration

OSPF - point-to-multipoint network type

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 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 E1 E2 N1 N2 routes

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 Recursion

OSPF LSA Sequence Numbers

OSPF LSA Types

OSPF NSSA ABR advertises default route

OSPF Not So Stubby Area NSSA

OSPF Path selection

OSPF Routing Bit

OSPF SPF Scheduling and throttling timers

OSPF TTL Security Check

OSPF Troubleshooting

OSPF Type 4 LSA

OSPF Type 5 LSA

OSPF Type 7 LSA

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 immediate hello packet

OSPF in a GRE multipoint environment

OSPF loop prevention

OSPF master slave election

OSPF message options field

OSPF metric sum of outgoing interface costs

OSPF modifying the router ID

OSPF network command

OSPF - route summarization

Links to this page: