OSPF Administrative Distance, or OSPF AD, is the key of electing OSPF among other routing protocols (if existed) leading to the same target within the same routing table, in this blog post we will discover the basics and types of Administrative Distances for OSPF across multiple different platform.
Administrative Distance
For Cisco systems operating systems, regardless of their platforms, all the IOS-XE, IOS-XR, and NX-OS OS's treats OSPF based on the "AD" which has the value of "110". Now the most important thing is not just to know the numerical value which will be useless without knowing its order of preference among the other routing protocol Administrative Distances.OSPF AD with Cisco OS's
The values will be as follows regarding the Static and Dynamic Routing Protocols:- Direct = 0
- Static = 1
- eBGP = 20
- EIGRP = 90
- OSPF 110
- IS-IS = 115
- RIP = 120
- iBGP = 200
Route Preference
Dealing with devices/platforms from Juniper Networks will get you to face and operate with JunOS, the one unified operating system they have, across their different platforms. with juniper the concept of Administrative Distance still exists and still play the same role, but instead, they name it only differently here by calling it as "Route Preference".OSPF AD with Juniper JunOS
Some protocols will be treated differently here, and some others will be missing (cases like EIGRP as it is a Cisco proprietary).- Direct/Local = 0
- Static = 5
- OSPF internal = 10
- IS-IS L1/L2 = 15/18
- RIP = 100
- OSPF external = 150
- IS-IS external L1/L2 = 160/165
- BGP = 170
Routing Protocol Preference
With another operating system like Huawei's Versatile Routing Platform (VRP) we will see many similarities with the one of JunOS, but there is a small difference to catch in the table described below.OSPF AD with Huawei's VRP
Still missing EIGRP here, check the surprise of where OSPF stands within the table:- Direct = 0
- OSPF = 10
- IS-IS L1/L2 = 15/18
- Static = 60
- RIP = 100
- OSPF external = 150
- BGP = 255
Route Preference Again
One more platform to check their preferences and that would be The Nokia Service Router Operating System (SR OS).OSPF AD with Nokia's SR OS
It has the same name and many similar numbers to Juniper's JunOS table:- Direct = 0
- Static = 5
- OSPF = 10
- IS-IS L1/L2 = 15/18
- OSPF external 150
- IS-IS external L1/L2 = 160/165
- BGP = 170