NAC In-band Real IP Gateway process

Question

Hi all,
I've been doing a lot of research and I still can't find good answers to some of my questions. All the big questions are answered for out-of-band configuration but I find that it's assumed that understanding in-band is taken for granted lol...I guess I'm slow =P
How does In-band Real-IP Gateway work?
What is the point of the /30 subnets?
Are there access/auth VLAN pairs in in-band configurations?
How does quarantining work?
I read that the NAC Server can only send traffic out the untrusted port in one VLAN and that you aren't allowed to trunk that port. Does this mean that there's no support for multiple untrusted VLANs mapped to a single NAC Server?
Can you do role-mapping with in-band configurations?
Any help with any or all of these questions would be GREATLY appreciated!
Thanks much =]
~ Xavier.

Answer 1

Hi Xavier,
let me try to answer your questions
1.How does In-band Real-IP Gateway work?
The CAS works in routed mode, so you have different IP addresses (on different subnets) on the trusted and untrusted interfaces. Since the CAS doesn't support routing protocols, all the routing has to be configured through static routes
2. What is the point of the /30 subnets?
The idea is to have small subnets for your clients so that with this IP config the clients in the authentication VLAN need to go through the CAS even to talk to other clients in the same L2 subnet.
Check here for some explaination:
http://www.cisco.com/en/US/docs/security/nac/appliance/configuration_guide/47/cas/s_dhcp.html#wp1057889
3. Are there access/auth VLAN pairs in in-band configurations?
If you ask if there's VLAN mapping, then the answer is NO, as the aim of the VLAN mapping is to *bridge* traffic between the trusted and untrusted mapped VLANs, but in Real-IP the CAS does L3 routing of the traffic.
4. How does quarantining work?
When a client is quarantined, this works in the same way as in OOB, as in this phase the client is still inline to the CAS.
So the concept is that the CAS assigns the user to the temporary or quarantine role and it applies a traffic policy that you configured for the temporary or quarantine role.
5. I  read that the NAC Server can only send traffic out the untrusted port  in one VLAN and that you aren't allowed to trunk that port. Does this  mean that there's no support for multiple untrusted VLANs mapped to a  single NAC Server?
The "single" VLAN restriction for Real-IP CAS applies only to the *trusted* side. The CAS can be the default gateway for multiple VLANs/IP Subnets on the *untrusted* side.
You configure additional VLAN/IP addresses on the untrusted side using the "managed subnet" configuration.
This is also mentioned here:
http://www.cisco.com/en/US/docs/security/nac/appliance/configuration_guide/45/cas/s_deploy.html#wp1050938
The Clean Access Server can manage one or more  subnets, with its untrusted interface acting as a gateway for the  managed subnets. For details on setting up managed subnets, see Configuring Managed Subnets or Static Routes, page 5-26.
6. Can you do role-mapping with in-band configurations?
Yes, you can do it! However, you cannot assign VLANs as you do in OOB but you can assign different access level based on the IP traffic policies and bandwidth restrictions you assign to the specific role.
Check for instance here for more details:
http://www.cisco.com/en/US/docs/security/nac/appliance/configuration_guide/45/cam/m_users.html#wp1040231
In a nutshell, irrespective of the use of InBand vs. OutOfBand:
- the clients are InBand to the CAS during the CAS discovery, authentication, posture assessment and remediation phases.
The main difference occurs when the user is authorized to have access to the network and you perform role assignment both in IB and OOB but..:
- in IB the client traffic keeps on flowing inline to the CAS, so you can apply different access policies (ACL) and bandwidth control policies depending on the role (but you cannot assign VLAN);
- in OOB the client traffic bypasses the CAS once it's authorized: in this case you can apply different VLANs but (since the CAS is no longer along the path) you can't apply ACLs and/or traffic shaping policies in this case.
I hope this answers your questions.
Regards,
Federico
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