L3Out in multipod

[Antonio Macia]

Hi,

I'm designing a two sites multipod setup where each site will have an L3out for redundancy purposes.

L3out at the main site will be always used for both sites. When a failure is registered at the main site, then the L3out at the second site will take over. 

I create two L3out objects with their corresponding contracts, one per each location. Should I consume both contracts at every EPG to achieve the desired redundancy? What is the best practice in this regard?

Thanks.

[6askorobogatov]

I assumed that you have the  same destinations for both of your L3Out and the same subnet(s) in NetEpg for both.  In this case  you better  create one L3Out  with multiple Logical Node Profiles and  put different preferences on the route, preferring the primary one.  That is not just an idea, it what i did multiple times.  

[Antonio Macia]

Hi 6askorobogatov,

Thanks for your reply.

Yes, I have just a single external network (0.0.0.0/0) for both PODs. Two border leaf switches at each pod connect to the external network using an L3 port-channel each one. In this case, I should create 4 x Node Profiles where two of them (Main POD) won't have any route-map applied and the other two (Secondary POD) will have an import route control route-map.

The import route control will have a set action that increases the metric. Is this approach correct?

Regards.

Thanks.

[6askorobogatov]

You will need 2 node profiles.   If you have PC/VPC, that is you interface you are creating node profile for and use PC/VPC in logical interface profile. 

For the rest of the config,  such  as route-map you need to provide a bit more  specifics. BTW, route-map is property of L3Out, not the specific node profile and has nothing to do with routing decision. 

 General, if you are using default gateway (0/0), you can use static route - prefix 0/0 and preference (1-255) that will define ...well...route preference.  

Another thing, for Net-EPG 0/0 you will need to use contract only, preferred group will not work with 0/0

[Antonio Macia]

Hi,

"BTW, route-map is property of L3Out, not the specific node profile and has nothing to do with routing decision"

Then, I would need two different L3Out with different route-maps applied and that would take me to my initial question about consuming two L3out contracts. 

" General, if you are using default gateway (0/0), you can use static route - prefix 0/0 and preference (1-255) that will define ...well...route preference"

I'm running OSPF because I'm advertising internal fabric subnets to the rest of my network and also receive not only the 0/0 but some additional prefixes as well and I want to influence all the prefixes altogether.

Is there any way of doing this with a single L3out?

[6askorobogatov]

Sorry, I still not clear what you are trying to accomplish.  Are you planning to advertise/receive different prefix list in 2 sides ? If not, why you need 2 route maps ?

Do you have any other L3Out in routing realm, you are planning to have 0/0 L3Out ? If no, why you need to receive any routes, if it follows default route ?  If you just need to advertise via OSPF some of the ACI subnets  and want externals (and ACI) to prefer one path over other, you can do it in OSPF config. 

[Antonio Macia]

Apologies for the confusion. Let's keep it simple. Let's imagine I create a single L3out with two node profiles, one per each POD. Now I want to force all the POD2 traffic to use the default route at the POD1. How can I accomplish this?

Thanks.

[6askorobogatov · Accepted solution]

OK. In this case, you can use different preferences on the static route, there are number of options for BGP (however it is a bit truncated in ACI) and, i guess OSPF area cost for OSPF.