EIGRP IWAN / STUB SITE

[morph.andy]

Hi 

firstly apologies for this question

I cannot get my head round the WAN stub site command.  I get the stub router function, and benefits etc.  But every time I read about wan stub site, it throws me and I dont get it.  If its some sort of stub command that stops the wan interface from receiving eigrp routes. wouldn't you use a passive interface in that case ?

reading the cisco documentation : .

This eigrp stub-site command resets the peers on WAN interfaces and
initiates relearning of routes from WAN neighbors

This confuses me - help

Can someone explain it to me, as if I was a 2 year old dog

[MHM Cisco World]

see comment below

[Joseph W. Doherty]

Unsure what to "say", as you write you understand a stub's benefits.  However you also ask why couldn't a passive interface be used.  So, I suspect you might not fully understand a stub with a routing protocol especially as you wonder why a passive interface could not be used.

Taking passive interface question first, passive blocks routing protocols between devices, and we don't want to block such between the stub router and its upstream router; because we still want to exchange routes. BTW, basically the same need if non stub edge.  Also, likewise, we could/should make passive edge networks, those without another router to exchange routes with.

Actually, routing wise, the real difference between a stub setup vs. non-stub, the former usually only get (dynamically) a default route while the latter may receive lots and lots of routes.

Perhaps, your questions are based on thinking there must be more to it, but maybe not.

If the forgoing doesn't help, please try to further describe what's unclear.

[morph.andy]

Hi - thanks for responding

its the actual

wan stub site

command im struggling with.  

#stub site wan interface

- i dont under stand the relevance of it. 

Appreciate the WAN interface is leaving your network say, but whats that command actually doing ?

[Joseph W. Doherty]

Ah, gotcha, I think.

It appears, to me, to be another variant of EIGRP stub (which it's mutually exclusive with).

Documentation mentions tagging routes received on a particular interface, when command is used on a particular interface.  (If routes are newly tagged, that might be why mention is made of "relearning" routes from other routers.)

I'm guessing, since it's IWAN related, such route tagging helps/assists IWAN in doing whatever it does when using IWAN.

Additional clarification might be obtained from those using EIGRP and IWAN.

[morph.andy]

HI - yeah that seems to be the case - it will tag a route coming in on a wan interface (which has the command on it) and wont advertise it out another wan interface (which also has the command on it), but it will then advertise that router downstream...now that bits confusing me as how is that a stub lol.

[MHM Cisco World]

I will run lab and share with you what benefits and different between stub and passive interface 

[morph.andy]

thanks - thats ok, its the actual stub site on wan interfaces which was puzzling me.  I was hopeing to set a lab up as well, but looks like my IOS doesnt support it under named eigrp

[David Ruess]

Hello,

After looking around I think this should help you.

https://netacad.fit.vutbr.cz/wp-content/uploads/ccnp/ce2/ENARSI_Chapter_3.pdf

Slide 29/30 explained it like this:

The EIGRP stub site feature builds on EIGRP stub capabilities that allow a router to advertise itself as a stub to peers only on the specified WAN interfaces but allow it to exchange routes learned on LAN interfaces. 

The point of a stub it mainly so routers don't use it as a transit device and it limits the query domain when the router loses a route. So its basically the STUB router setting but advertising as a STUB to only specific peers (i.e. WAN peers) so they don't try to query across the WAN and eat up BW. But local routers can query them if they lose the route. Looks like its designed for when multiple routers at a Branch site have WAN connections. If one loses its WAN connection it can query the neighbor Branch router for the routes since it will have them but a Hub router cant query it across the WAN if it loses a route since its advertising itself as a stub to the WAN side and a normal neighbor to the local neighboring branch router

Give it a read and hope that helps

P.S. never heard of it until now but looks really useful.

-David

[morph.andy]

Thanks mate ! appreciate - will check.  That netcad looks really useful...wonder if thats free

[David Ruess · Accepted solution]

No problem. Not sure if Netacad is free but I just looked at those slides for reference. Also I did lab this up and it did exactly as described above., It advertised a STUB status to one neighbor (configured on interface towards neighbor) and it advertised itself as a regular neighbor to its other connected neighbor. 

If any of the provided answers from community members helped please make sure to mark post as solved to help others in the community with similar issues.

-David

[Joseph W. Doherty]

A very nice reference, indeed!

Basically it appears prior EIGRP stub routers were just that, stub routers.  The latter stub-site, appears to (somewhat) mimic OSPF stub areas, i.e. multiple routers can be within the stub-site (also somewhat like OSPF, the stub-site routers for the same site should have the same ID, much like OSPF routers having the same area ID).  I.e. the stub-site router is (somewhat) like an OSPF stub ABR, using the interface command stub-site wan-interface to denote the interface(s) that connect to the (somewhat) OSPF area zero core (as EIGRP doesn't have ABRs).

"P.S. never heard of it until now but looks really useful."

Yea, it seems a relatively new feature and, yea, I could see it being useful, that's if you're using EIGRP.  ; )

[morph.andy]

Do you mind me asking which lab u used - as i dont get the option for that on the IOS im using

[David Ruess]

I used my CML (Cisco Modeling Labs) IOS devices. I already had a practice lab up with named EIGRP neighbors, so I tested out the command. I don't have access to them now, but I have it running at home. I will be glad to share the screenshots once I am able to.

IOSv

IOS classic layer 3 image

15.9(3)M6

-David

[MHM Cisco World]

Yes I also interested in this lab