Question about redistribution process

[christianpho]

HI,

I'm studding for CXCNP certification exam. For this I'm usign Cisco Modeling Lab, in which I build an IPv6 network, the biggest par of the network is using OSPFv3 seperate un 5 area (AREA0 plus 4 others).

I had simulilate the biggest network compagny acquired another compagny running with EIGRP with IPv6.

At to point of the network, I redeistribute OSPF into EIGRP, and EIGRP into OSPF.

On one location I choose to redistribution to be thge ABS of AREA3. The other redistribution point is an internal router in AREA2.

The EIGRP network is using prefix 2002:DB9::/36.

The network 2002:DB9:CAF3:4::/64 is the point to point network between ASBR connected to AREA3. The interface is only annonced into EIGRP protocol.
The network 2002:DB9:CAF3:5::/64 is the point to point network between ASBR connected to AREA2. The interface is only annonced into EIGRP protocol.

In OSPF domain I'm redistributing EIGRP as type 1.

Now, when I'm look at routing table of router in AREA0, on one router directly connected to ASBR of AREA3, I find all routes to 2002:db9:/32 are pointing to the connected ASBR, except for 2002:DB9:CAF3:4::/64 prefix which
prefer route to AREA2.

My suspition is this, I haven't configured redistribution for connected routes.

But, if I'm configuring connected routes, I'm also cgoing to redistrebute connected routes on which no routing protocol is enable, which it might not what I want... (But in my case it won't change anything since all interfaces are in OSPFv3 or EIGRP domain.)

I was understood that when I'm redistribution EIGRP protocol I'm going to redistribute all EIGRP topologie perspective including connected interface under which EIGRP is enable. (I haven't check yet, but I suppose ythat I'm going the observe similar behavior for OSPF route being redistributed into EIRGP.

When configuring redistribution, how should specified that local EIGRP interface network should also be include in the redistribution process ?

I had attached the complete CML lab topology and equipement configuration for providing complete case explanation. I also going to attached VISIO diagram.

Thank you for your help.

[Elliot Dierksen]

I don't see the topology, but I will share my opinion from many years in the trenches. Redistributing one protocol into another has a lot of different ways for you to shoot yourself in the foot, so it is (IMHO) something to be avoided if at all possible. You might have 5000 different routes in your network, but your spoke router with a single WAN connection doesn't need every single one of them. It just needs a default or summary route to get it back to the core router(s) that has (and needs) a route to every network. It is actually counterproductive for that spoke router to have all the routes. It consumes memory needlessly, and makes the router traverse a much longer routing table when it only has one exit. Look at how the networks are structured, and see where you can do a summary. Do that summary in a limited number of places to minimize the chances for creating loops.

EIGRP to OSPF is a perfect example of that. Depending on how you redistribute it, you could have a case where the originating network trusts (lower admin distance) the EIGRP route redistributed route more than its internal OSPF router, and then you get a loop.

Also IMHO, but redistribute connected is rarely a good thing. If you want the routers to peer (EIGRP or OSPF), you must have a network statement with the same ASN/area (EIGRP/OSPF respectively). Thus there would be no need to redistribute connected.

[christianpho]

Hi Eliot, 

I had attached the file now, I don't what yesterday why the file haven't been uploaded anyway....

In the case of my post independently if redistribution is or is not a good idea to using it or not.  At the exam we should be able to implement and troubleshoot 2 way redistribution.

In my scenario, it was the case a Compagny A acquire Compagny B, so should be considere as a temporal solution during time of compagny merging network and /or replacing equipment if some has to be.  

[Georg Pauwen]

Hello,

there are no attachments, post whatever you have so we can get a better picture of what might happen...

[Giuseppe Larosa]

Hello @christianpho ,

what you see is specific of IPv6 redistribution you need the keyword include-connected to have a behaviour similar to IPv4.

see

https://www.ciscopress.com/articles/article.asp?p=2273507&seqNum=8

Hope to help

Giuseppe

[christianpho]

Thank you Giuseppe, 

Do you know the inclusion of the connected interface is not the default behavior ?  From my own point of view it would be more natural, but it might have technical reason to have different default behavior.

Thank you!

[Giuseppe Larosa]

Hello @christianpho ,

>> Do you know the inclusion of the connected interface is not the default behavior ? From my own point of view it would be more natural, but it might have technical reason to have different default behavior.

From my studiies for CCIE recertification I remember so : that in IPv6 the include-connected parameter is nedeed to have an IPv4 like behaviour.

The reasons for different behavious are probably related to the fact that with IPv6 mutiple IPv6 addresses / subnets can be supported on the same interface not only of different types ( link local , unique local and global ).

The routing protocols neighborships are built using link local addresses to make it easier more plug and play.

Hope to help

Giuseppe

[christianpho]

Hi, 

Also curiously after updating configuration of all router in AREA2 to be an NSSA area, the ABR of the AREA2 don't know route to 2002:db9::/32 from SITE-2 router where is the redistribution point with EIGRP domain.  The Site-2-2 router learn equal path route through EDGE-HQ-2 and through Site-2 while Site-2 is definitely a closer router.

On the rest of the lab configuration I have update the redistrbution in both to include connected interface as well on router EDGE-HQ-3.

Here attached the routing table and router configuration updated of router has at least one interface in AREA2....