EIGRP Summary Route with AD 5

notun1

Hi
I am not so clear why EIGRP summary route has AD 5 and How it's affecting the routing table when you have more specific route for that summary?????
Regards,
Notun

Daniel333

Well, more specific is always going to win out. No matter the AD.

If there is a route to 192.168.0.0/16 coming from a few different routing protocols it's going to choose the lowest AD of the options it has.

But if you get 192.168.1.1/24 even if it's from RIP over a 64k link its going to choose that over any less specific address, even if it's a 10gig link from EIGRP or anything.

I think that is what you are asking?

notun1

Daniel333 wrote: »

Well, more specific is always going to win out. No matter the AD.

I understood more specific route always win whatever AD is..

If there is a route to 192.168.0.0/16 coming from a few different routing protocols it's going to choose the lowest AD of the options it has.

I am thinking about the local router where the EIGRP summary is implemented as AD 5 is locally significant. If I am using different routing protocols then EIGRP summary route still not being used as it will be using more specific route of that summary.(D 192.168.0.0/16 is a summary, 00:00:58, Null0--discarding route)

That's Ok. My question is how the AD 5 affecting the routing table if I am only using EIGRP as I know AD is Locally significant. I mean what is the use of AD 5 in a EIGRP summary route ?

Monkerz

notun1 wrote: »

That's Ok. My question is how the AD 5 affecting the routing table if I am only using EIGRP as I know AD is Locally significant. I mean what is the use of AD 5 in a EIGRP summary route ?

The administrative distance metric (AD 5) is used to advertise a summary without installing it in the routing table.

In the end, the AD of 5 is a loop prevention mechanism thought up by Cisco. My best guess is with the AD of 5, rouge summary routes learned dynamically with the same prefix will not cause loops for the router will look at AD and the traffic will be toss at Null0. No other protocol as an AD lower than 5.

notun1

Monkerz wrote: »

The administrative distance metric (AD 5) is used to advertise a summary without installing it in the routing table.

In the end, the AD of 5 is a loop prevention mechanism thought up by Cisco. My best guess is with the AD of 5, rouge summary routes learned dynamically with the same prefix will not cause loops for the router will look at AD and the traffic will be toss at Null0. No other protocol as an AD lower than 5.

Yes..I got it.Thanks..

isendel

Monkerz wrote: »

The administrative distance metric (AD 5) is used to advertise a summary without installing it in the routing table.

In the end, the AD of 5 is a loop prevention mechanism thought up by Cisco. My best guess is with the AD of 5, rouge summary routes learned dynamically with the same prefix will not cause loops for the router will look at AD and the traffic will be toss at Null0. No other protocol as an AD lower than 5.

The AD is not a loop prevention mechanism thought by Cisco. AD represents how "believable" the prefix is compared to others like OSPF (default AD 110) or statically configured routes (AD1) or learned through a redistribution from an EIGRP AS (AD170 by default). By having a value of AD the routing table selects the best AD (lowest) and installs it in the routing table if no other "more specific route" to that network exists. If a more specific route to a network exist than that route will be preferable regardless of the AD it may have. I hope if was not too confusing.