Editing Open Shortest Path First (section)

== OSPF over MPLS VPN  ==
[[File:OSPF with BGP-MPLS VPN backbone.svg|right|frameless|400x400px]]
{| class="wikitable  floatright mw-collapsible" style="width: 500px;"
|+ [[Border Gateway Protocol#Communities|BGP extended communities]] transitive for OSPF<ref>{{Cite web|title=Border Gateway Protocol (BGP) Extended Communities|url=https://www.iana.org/assignments/bgp-extended-communities/bgp-extended-communities.xhtml|access-date=2021-11-28|website=www.iana.org|archive-date=November 28, 2021|archive-url=https://web.archive.org/web/20211128105545/https://www.iana.org/assignments/bgp-extended-communities/bgp-extended-communities.xhtml|url-status=live}}</ref>

|-
! Type 
! Type field 
! sub value 
! name 
|-
| Two-octet [[Autonomous system (Internet)|AS]]
| 0x00
| 0x05
| OSPF domain identifier
|- 
| Four-octet [[Autonomous system (Internet)|AS]]
| 0x02
| 0x05
| OSPF domain identifier
|- 
| IPv4 address
| 0x01
| 0x05
| OSPF domain identifier
|- 
| IPv4 address
| 0x01
| 0x07
| OSPF route ID
|- 
| Opaque
| 0x03
| 0x06
| OSPF route type
|}
{| class="wikitable  floatright mw-collapsible" style="width: 300px;"
|+ BGP extended communities<br />
Attribute for OSPF route type 
|-
! width="66%" | 4 byte || width="12%" |1 byte  || width="12%" |1 byte 
|-
|-
| style="text-align: center;" |Area number
| style="text-align: center;" |Route type
| style="text-align: center;" |Options
|}

A customer can use OSPF over a [[MPLS]] VPN, where the [[Network service provider|service provider]] uses  BGP or RIP as their [[interior gateway protocol]].{{Ref RFC|4577}}
When using OSPF over MPLS VPN, the VPN backbone becomes part of the OSPF backbone area 0. In all areas, isolated copies of the IGP are run.

'''Advantages''': 
* The MPLS VPN is transparent to the customer's OSPF standard routing.
* Customer's equipment only needs to support OSPF.
* Reduce the need for tunnels ([[Generic Routing Encapsulation]], [[IPsec#Tunnel mode|IPsec]], [[wireguard]]) to use OSPF.

To achieve this, a modified OSPF-BGP redistribution is used. All OSPF routes retain the source LSA type and metric.<ref>{{Cite web|title=MPLS VPN OSPF PE and CE Support|url=https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_l3_vpns/configuration/xe-16-10/mp-l3-vpns-xe-16-10-book/mpls-vpn-ospf-pe-and-ce-support.html|access-date=2021-11-28|website=Cisco|language=en|archive-date=November 28, 2021|archive-url=https://web.archive.org/web/20211128135250/https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_l3_vpns/configuration/xe-16-10/mp-l3-vpns-xe-16-10-book/mpls-vpn-ospf-pe-and-ce-support.html|url-status=live}}</ref><ref>{{Cite web|last=Cisco|title=Using OSPF in an MPLS VPN Environment |url=https://www.racf.bnl.gov/Facility/TechnologyMeeting/Archive/06-30-04-CISCO/Using-OSPF-in-MPLS-VPN-Environment.pdf |archive-url=https://ghostarchive.org/archive/20221010/https://www.racf.bnl.gov/Facility/TechnologyMeeting/Archive/06-30-04-CISCO/Using-OSPF-in-MPLS-VPN-Environment.pdf |archive-date=2022-10-10|access-date=2021-11-28|url-status=live}}</ref>
To prevent loops, an optional DN bit{{Ref RFC|4576}} is set by the service provider in LSAs from the provider equipment to indicate that a route has already been sent to the customer's equipment.