Administrative Distance Explained for Beginners

Administrative Distance is a measure used by routers to select the best path when there are two or more different routes to the same destination from more than one routing protocol.

The route which is having the lowest AD value will make its entry in the routing table.

N.B.- If a specific route is being learned by a routing protocol which is having higher AD value will be entered in the routing table instead of the summary route being learned by a routing protocol which has lower AD value due to the longest prefix match rule of routing.

The following will provide the default AD value of different routing protocol:

Directly Connected Routes:                 0
Static route out an interface:             1
Static route to Next-Hop address:          1
EIGRP Summary Route:                       5
External BGP:                              20
Internal EIGRP:                            90
IGRP:                                      100
OSPF:                                      110
IS-IS:                                     115
RIP:                                       120
EGP:                                       140
ODR:                                       160
External EIGRP:                            170
Internal BGP:                              200
DHCP Learned:                              254
Unknown:                                   255

N.B.- If the Administrative Distance is 255, the router does not believe the source of that route and does not install the route into the routing table.

Architect/Consultant in IT/Telecom/Networking Support Industry with over 13+ years of Experience. Mainly working with Cisco Products other than Cisco worked with VMware NSX/Juniper/Riverbed/Meraki & Citrix Products, and worked with various clients like PSU Banks, Petroleum Corporations, different government sector clients, BPO Sector, Telecom NOC and ISP. Global Certifications: VMware vSphere Foundation 6 CCNA Routing & Switching CCNP Routing & Switching ITIL V3 Foundation RTSA-W RTSS-W RSA RTSA-NPM RTSS-NPM Aspiring Certifications: VCP-NV

2 thoughts on “Administrative Distance Explained for Beginners

  1. Well explained. .I liked the post. Can you share basic entry level interview questions on routing and switching

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