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ISM CGN ServiceApp and address pool limitations

Is there any ServiceApp limitation regarding ServiceApp interfaces on ISM compared to CGSE on CRS?

If I understand documentation for ISM correctly, only ServiceApp pairs cane be configured on ISM. Meaning only one inside VRF mapped to only one outside VRF.

I know that on CGSE you can map multiple inside VRFs to one outside VRF as long as you have different address pools, on ISM not. Configuration guide explicitly says that ServiceApp interfaces must be pared in N,N+1 or N,n+5 or N,+N+9. Is this true?

Regarding address pool. Is it possible to assign two IP ranges to one inside-to-outside mapping? Can I add together /19 and /20 ranges to be used together for single inside VRF without splitting customers in two VRFs.


Everyone's tags (4)
Cisco Employee

ISM CGN ServiceApp and address pool limitations


the statement for the pairing in the serviceApp numbers is correct. And yes, it's specific to the ISM, and not relevant for CGSE.

Today, we can not assign more than a map-pool per inside-VRF, this feature will come in a future release.



Hi, nicholas: I'm on XR 5.1

Hi, nicholas:


I'm on XR 5.1 right now doing nat44; according to docs multiple pools per vrf is supported starting with 5.2, right?


If upgrade is not an option, what would be best solution?


1.- create a second inside vrf




2.- create a separate serviceapp (in/out) pairing and add second inside vrf in the same cgn nat44 service while using abf do distribute traffic between the 2 separate inside VRFs with separate/different map address-pools?





Hi Carlos,Where did You find

Hi Carlos,

Where did You find information, that multiple pools per vrf are supported starting 5.2 ? Couldn't find in release notes..

Regarding your question. I can share our experience.

We are using option 1. We have created 2nd inside vrf.

On the outside there is one vrf BGP with 2 serviceapp interfaces, but on the inside 2 different vrf's, with 1 serviceapp each. Traffic is redistributed between inside vrf's using ABF.

Even IP are forwarded to C1, odd - to C2 

 1260 permit ipv4 any nexthop1 vrf C1 ipv4 10.20.x.y nexthop2 vrf C1
 1270 permit ipv4 any nexthop1 vrf C2 ipv4 10.20.a.b nexthop2 vrf C2

Hi, Marks: It's in the

Hi, Marks:


It's in the configuration guide for 5.2 and 5.3:


Thanks for sharing. What you suggest is what we ended up doing since we are on 5.1.



Cisco Employee

Hi Carlos,my bad, totally

Hi Carlos,

my bad, totally missed your post/question.

One important correction: the multiple pool feature is ONLY available on the CGSE+ running 5.2.0 onwards. It is NOT supported on ISM cards.

The only solution on ISM is to multiply the number of VRFs (each one with a particular pool range).



Thanks a lot, Nicolas. By ISM

Thanks a lot, Nicolas.


By ISM, you mean ISM/VSM, correct? Do you know when it'll be available on that card?

Cisco Employee

Indeed, it's the same

Indeed, it's the same situation for ISM and VSM. AFAIK, it's not in the short term roadmap. So I can only suggest to contact your Cisco account team representative and get him/her relay your interest to the Product Management team.



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