Welcome to another one of our blogs on the configuration of the new series of WLC from Cisco the C9800!
In this post, I want to go through with you an issue that I ran into when configuring a Guest SSID which was using MAB with a CWA to redirect to a portal on ISE.
A high-level overview of the C9800 -40 + 3800i APs – Local mode, Central Switching & Authentication. ISE was configured correctly and was working correctly as it should of the AireOS 5508 that I was replacing and was still working.
I had followed all the steps & configured everything in this Cisco guide apart from the BYOD flow as that was not a requirement for this project.
Cisco guide: https://community.cisco.com/t5/security-documents/ise-and-catalyst-9800-series-integration-guide/ta-p/3753060
But I was hitting two scenario issues – the first one was that I was not being redirected to the portal when connecting to the SSID but I was authenticated on ISE and had internet. The second was that I was being redirected and could authenticate with ISE by inputting the code but then not getting any internet after.
The configuration for the first scenario where I was not getting redirected but I was authenticated and had internet was that I had created the “Redirect_Webauth_ACL” and that was applied globally on the WLC – very much the same as you would on AireOS.
The configuration for the second scenario where I was being redirected but then not getting any internet was that I had applied the “Redirect_Webauth_ACL” to the “WLAN ACL” in the “Access Policy” of the Guest “Policy Profile”
So even though I had followed the documentation neither scenario was working how I would expect it to. I am going to take you through below in some screenshots the config I had applied and where as well as show you how I managed to get it working even though what I did was not clear from the Cisco guide.
One thing to call out here for when you come to write an ACL on the C9800 is to remember that they use the IOS syntax instead of what you would be used to on the AireOS WLCs.
From the Cisco guide this is an example of how to write the web auth redirect ACL – Cisco ACL example for the C9800:
This is where you configure the ACLs and can see that the ACL that I had configured for the web auth redirect is called “GUEST_REDIRECT_ACL”
We can have a look at the redirect ACL rule here and can see that I have specified the two ISE servers and DNS (I had previously made the ACL more specific but after many hours of troubleshooting I decided to make it bit more open)
Now I want to show the WLAN config where you can see the Authorisation & Authentication lists that have been specified are the two ISE servers:
Now in this scenario where I was being authenticated but not redirected, in the policy profile for the guest I had not specified the redirect ACL here.
When I did specify the redirect ACL in the access policy above I was now being redirected but then was not getting any internet.
Checked the guide again to make sure everything was correct which it seemed it was so left me scratching my head at this point as to why was not working as expected.
So I reached out to my security friend Aref who skills far surpass mine when it comes to security & ISE to double-check ACL config & ISE policies for the Guest Wireless MAB.
Here are a few screenshots of how ISE is configured:
So Aref confirmed that all looked good from an ISE configuration perspective – so how did we get it working I hear you ask, great question! What we had to do was to specify another ACL which we called “DENY_GUEST_INTERNAL” which in this rule we basically blocked any access to RFC 1918 but then allowed anything else and we applied this ACL to the Guest “access policy” in the “policy profile” with the redirect just applied at a global level and now we finally got redirected as well as internet!
Here are some screenshots of the other ACL, its configuration and where we applied it:
It was quite a long day of troubleshooting and trying different scenarios before we managed to finally get it working as expected and I feel that the way we did finally manage to get it working was not clear from the Cisco documentation so hopefully this can help save you guys some time if you have to configure a guest network with CWA + MAB and run into the same scenarios as I did.
Hope you enjoyed this blog on another configuration gotcha from the C9800 – as we deploy more of these and find anything else that we think may help others who will be implementing these for the first time we will post more blogs with our findings!