> ## Content Index > Fetch the complete content index at: https://www.pinglabz.com/llms.txt > Use this file to discover other available public pages before exploring further. # EIGRP Administrative Distance: 90, 170, and 5 - URL: https://www.pinglabz.com/eigrp-administrative-distance/ - Published: 2026-07-10T13:00:00.000Z - Updated: 2026-07-10T13:00:00.000Z - Author: Jaime - Tags: EIGRP, Fundamentals, #Import 2026-08-01 19:54 EIGRP does not have one administrative distance, it has three. That surprises people who memorized "EIGRP is 90" for an exam, then watched a redistributed route show up as 170 or a summary route as 5\. The three values are not a quirk; each one encodes a deliberate trust decision. This post explains all three EIGRP administrative distances, why they differ, and how to read and change them. For the cluster overview, see the [EIGRP complete guide](https://www.pinglabz.com/eigrp/). ## Administrative distance, in one paragraph A router often learns the same destination from more than one source - say, OSPF and EIGRP both have a route to 10.0.0.0/8\. The metrics of those protocols are not comparable; an OSPF cost and an EIGRP composite metric are different units. Administrative distance (AD) is the tie-breaker. It is a number from 0 to 255 that ranks how much the router *trusts* each routing source. Lower AD wins, and the winning route is the one installed in the routing table. AD is strictly local to one router and is consulted before metric ever enters the picture. ## EIGRP's three administrative distances EIGRP internal AD90 What it is A route learned from another EIGRP router within the same EIGRP autonomous system EIGRP external AD170 What it is A route redistributed into EIGRP from another source (OSPF, BGP, static, a different EIGRP AS) EIGRP summary AD5 What it is The local summary (aggregate) route EIGRP creates when you configure manual summarization One protocol, three numbers, three different meanings. Memorizing "EIGRP equals 90" is only correct for one of the three cases. ## Why internal is 90 AD 90 is EIGRP's default for routes it learned from a fellow EIGRP router. It is a low number on purpose - lower than OSPF's 110, lower than RIP's 120, lower than IS-IS's 115\. When EIGRP and another IGP both offer the same prefix, EIGRP's internal route wins. That reflects Cisco's design intent: EIGRP is meant to be the preferred IGP where it is deployed. ## Why external is 170 AD 170 applies to routes that were **redistributed** into EIGRP from somewhere else. The gap between 90 and 170 is deliberate, and it is about trust. An internal EIGRP route was computed by EIGRP's own DUAL algorithm end to end - EIGRP knows the full picture. An external route arrived from another protocol with a metric EIGRP had to translate, a metric that does not carry the same guarantees. Redistribution is also a classic source of routing loops, especially with mutual redistribution between two protocols at two points. By giving external routes a much worse AD (170, worse than OSPF's 110 and RIP's 120), EIGRP ensures that if a redistributed copy and a natively-learned copy of the same prefix both exist, the native one is preferred. The 170 is a loop-prevention safeguard, not an arbitrary penalty. ## Why the summary route is 5 AD 5 is the one that looks wrong until you see what it is for. When you configure manual summarization on an interface, EIGRP creates a **local summary route** for the aggregate and points it at `Null0`. That summary needs to win against the more specific component routes for the summarization to behave - and AD 5 (lower than internal EIGRP's own 90) guarantees it does. The Null0 summary is also a loop-prevention feature: a packet matching the summary but not any real component falls through to Null0 and is dropped, rather than being forwarded back toward the summarizing router. AD 5 keeps that protective summary firmly in the table. You will see it as a route to Null0 in `show ip route`. ## EIGRP against the other protocols Connected interface 0 Static route 1 EIGRP summary 5 eBGP 20 EIGRP internal 90 OSPF 110 IS-IS 115 RIP 120 EIGRP external 170 iBGP 200 ## Reading it on the router In `show ip route`, the AD is the first number in the bracketed pair. The route code letter tells you the EIGRP flavour: `D` is internal EIGRP, `D EX` is external EIGRP. ``` R1# show ip route eigrp D 10.20.0.0/24 [90/3072] via 10.30.30.2, 00:12:04, GigabitEthernet0/1 D EX 172.20.0.0/16 [170/3328] via 10.30.30.2, 00:09:51, GigabitEthernet0/1 D 10.40.0.0/16 is a summary, 00:14:22, Null0 ``` Read the brackets as `[AD/metric]`. The first line is internal (90), the second is external (170), and the summary route to Null0 carries AD 5. ## Changing the AD EIGRP's administrative distances can be overridden under the routing process with the `distance eigrp` command, which takes the internal value first and the external value second: ``` router eigrp PINGLABZ address-family ipv4 unicast autonomous-system 100 topology base distance eigrp 90 170 ``` Changing AD is occasionally necessary - for example, to make a backup path through another protocol preferred, or to control which route wins during a migration - but it should be deliberate and documented. Inconsistent AD changes across routers are a reliable way to create a routing loop. ## Common gotchas A redistributed route is being ignored in favour of another protocol It is EIGRP external, AD 170 - worse than OSPF (110) and RIP (120). Expected behaviour. An unexpected route to Null0 appears That is the EIGRP summary route, AD 5\. It is a feature of manual summarization, not a fault. EIGRP route wins over a static route you wanted A static route is AD 1 and should win. If it does not, check the static is actually valid and installed. Two EIGRP ASes exchange routes and they show as external Routes redistributed between two EIGRP autonomous systems are external (170), not internal. A loop after redistribution despite AD 170 AD only protects per-router. Mutual redistribution still needs route tagging and filtering. ## Key takeaways EIGRP has three administrative distances, each encoding a trust level. Internal routes are AD 90, low enough to beat OSPF, IS-IS, and RIP, because EIGRP computed them end to end with its own algorithm. External (redistributed) routes are AD 170, deliberately worse than the other IGPs so a native route always beats a redistributed copy - a loop safeguard. The local summary route is AD 5, low enough to beat EIGRP's own internal routes so manual summarization and its protective Null0 route hold. Read the AD as the first number in the `[AD/metric]` bracket of `show ip route`, and change it only deliberately, with `distance eigrp`. For the EIGRP cluster, see the [EIGRP pillar](https://www.pinglabz.com/eigrp/).