Tag Archives: EAS

ActiveSync, Intermediate Certificates and You

Recently, a customer called with ActiveSync issues. They had installed the certificate with the proper Subject and SAN entries on the Exchange server, but were unable to synchronize their Windows Phone 7 devices with Exchange 2010; iPhone and Android device encountered no issues.

A quick run of the Exchange Remote Connectivity Analyzer (ExRCA) showed the following:

Capture1 - Ano

As ExRCA discovered, not all certificates of the certificate chain were offered by the server. A quick inspection of the certificate showed the following certification path:

CertChain

In this example, the certificate authority (CA), GlobalSign, uses an intermediate CA, GlobalSign Domain Validation CA – G2, to delegate the process of creating UC certificates. Consequence is that the certificate of the root CA, in this example GlobalSign, as well as the certificate of the intermediate CA, here , must be present on the device or should be offered when setting up the connection so the client can validate them.

Inspection of the Exchange server showed that the intermediate certificate was properly installed on the Exchange server, after the customer imported the Personal Information Exchange File (.pfx) file, provided by the CA as part of the certificate package, which contained all certificates in the chain: root CA, intermediate CA and the UC certificate.

CertIntermediate

Then, investigation moved to the reverse proxy, in this case ISA Server 2006 SP1. It turned out the intermediate certificate on the ISA server, or rather the lack of it, was causing the issue. The customer had imported the individual UC certificate on the ISA server. Because the ISA server didn’t contain the intermediate certificate, it couldn’t send it to the client as part of the certificate chain. After importing the intermediate certificate on the ISA server, ActiveSync started working.

Generally speaking, Windows Mobile or Windows Phone devices don’t contain intermediate certificates so be sure to install them on your Exchange servers as well as on your reverse proxies. Checking and validating intermediate certificates is a client thing and in this case the intermediate CA was available on the non-Windows Phone devices which explained the difference in behavior between Windows Phone, iPhone and Android devices.

Note that, depending on your situation, you may have never seen the above issue before. |This could be the case when you’ve been using certificates directly provided a root CA so far. When selecting your CA, this might be something to take into account as not all mobile devices behave identical as you’ve seen. Also, although lifetime of root and intermediate certificates is quite long, it is something you should manage properly in your environment as you have to an additional certifiate to watch (which might expire or be revoked). Also, depending on volume and mobile costs, sending down extra traffic through the wire/air could be something to take into account. If you don’t think this could be an issue because certificates are relatively small, there’s a reason Mini OWA’s so popular in some regions. Distributing certificates to clients might become a better alternative in those circumstances.

Finally, I want to recommend the excellent SSL Certificate Management & Troubleshooting Tool, provided by DigiCert. It cannot only indicate potential certificate issues like these, or wrongly imported certificates (e.g. user store instead of computer store), but also fix them. As an alternative to ExRCA, you could use the online SSLchecker provided here.

Loadbalancing, ActiveSync and Affinity

Recently, a client was experiencing load issues on the Exchange 2010 Client Access Servers. The client also had installed a hardware load balancer to balance client traffic.

While investigating the PAL results, the ActiveSync connections chart showed a significantly unbalanced number of ActiveSync connections between the CAS servers.

It turned out the client had load balanced all client traffic using Source IP affinity for all protocols. This means each client gets assigned the same CAS server, based on the client’s IP address. While this may sound reasonable, for ActiveSync this may not be optimal. Reason is that most mobile telephony providers use some form of NAT translation for their clients, resulting in these devices to appear having the same IP address.

When organizations standardize on a NAT utilizing mobile telephony provider, the problem might emerge sooner as all of their mobile clients will be assigned to the same Client Access Server.

In the picture above you’ll see the top two mobile devices are being NAT’ed. When the top device connects to the Exchange environment, it gets assigned the 1st CAS server based on its IP address. When the 2nd mobile device connects, the load balancer sees the same IP address after which it will direct that traffic to 1st CAS server as well.

While affinity is not required for ActiveSync, it is recommended since for each newly appointed CAS server, the notification subscription to the mailbox to be informed of updates would have to be recreated. Of course, this would result in a performance penalty and increased latency. Another option would be Session ID, but some EAS clients unnecessarily create a new SSL session ID.

After switching affinity from Client IP to Authorization HTTP Header the ActiveSync clients spread out more evenly. When using Authorization HTTP Header affinity, the load balancer uses the base64 encoded credentials as part of the http client request, e.g.

POST http://mail.eightwone.com/Microsoft-Server-ActiveSync/default.eas?Cmd=Sync&..
..
Authorization: Basic YW55IGNhcm5hbCBwbGVhc3VyZS4=

After switching affinity for ECP as well (should be Cookie or Session ID), the load issues were gone.

Where in the past mobile clients were insignificant to Outlook clients when compared in numbers, the ongoing consumerization of IT movement results in an increasing mobile client population. The number of ActiveSync users may easily outweigh the number of Outlook clients, as many users use a phone or tablet (or both) in addition to Outlook, if they use Outlook at all.

Exchange ActiveSync and Inheritable Permissions issue

The issue and solution described here is by design, but not known by every customer so here’s my short write-up on this subject.

Recently, I was at a customer reporting issues with several users not being able to synchronize their mobile devices using ActiveSync. The customer was running Exchange 2010 SP1 and used various mobile devices, e.g. iPhones as well as Android phones and tablets. A quick look in the IIS logs revealed that devices were connecting properly, but they received HTTP return code 403 (forbidden):

2011-08-30 10:09:31 172.16.10.12 OPTIONS /Microsoft-Server-ActiveSync/default.eas User=XXXXX&DeviceId=d849cec9be024c828b9af73da93bb59b&DeviceType=htcbravo&Log=LdapC2_Error:UserPrincipalCouldNotBeFound_Dc:dc.domain.com_Budget:(D)Conn%3a1%2cHangingConn%3a0%2cAD%3a%24null%2f%24null%2f0%25%2cCAS%3a%24null%2f%24null%2f0%25%2cAB%3a%24null%2f%24null%2f0%25%2cRPC%3a%24null%2f%24null%2f0%25%2cFC%3a1000%2f0%2cPolicy%3aDefaultThrottlingPolicy%5Fe205201e-d418-409a-a15b-4b51baef9bf4%2cNorm%5bResources%3a(DC)dc.domain.com(Health%3a-1%25%2cHistLoad%3a0)%2c%5d_ 443 domain\XXXXX 62.140.137.149 Android-EAS/0.1 403 0 0 124

Another clue was provided by the eventlog, which revealed MSExchange ActiveSync was reporting error 1053:

ss

The remainder of the message reads: “Make sure the user has inherited permission granted to domain\Exchange Servers to allow List, Create child, Delete child of object type “msExchangeActiveSyncDevices” and doesn’t have any deny permissions blocking such operations”. What happens when setting up ActiveSync is that Exchange tries to create a container named ExchangeActiveSyncDevices below the user object in Active Directory and will store in that container an MsExchActiveSync object for each ActiveSync device. Apparently Exchange doesn’t have sufficient permissions to create these objects.

To fix this, open up Active Directory Users and Computers. Now, to be able to inspect the security settings, we first need to activate Advanced Features if not already set. To do this, from the View menu option, select Advanced Features.

Next, navigate to the user object experiencing the issue. Open up Properties, select the Security tab and click Advanced.

image

Notice the Include inheritable permissions from this object’s parent is not set, the reason for Exchange not having any permissions on the object.

To fix the issue, simply check Include inheritable permissions from this object’s parent and click OK. You’ll return to the previous window where you’ll notice the Exchange Server account is now granted permissions on the object:

image

At this point, ActiveSync will work and Exchange will be able to create MsExchActiveSync objects in the ExchangeActiveSyncDevices container:

image

Note that Include inheritable permissions from this object’s parent by default is not enabled for members of the protected groups, e.g. Domain Admins. In fact, every hour the DACL on members of protected groups will be reset and inheritable permissions will be removed. This process is called AdminSDHolder which is to prevent inappropriate changes from being made to protected groups, accidently or otherwise.  Michael B. Smith did a nice write-up on this subject here. This is also the reason why bypassing the AdminSDHolder limitation by manually granting Exchange permissions would be inappropriate.

To prevent this issue, it is recommend to follow an old, yet far from rusty administrator best practice, which is to use one account for day-to-day operations, e.g. work and e-mail, and another account for administrative purposes.

Exchange & Windows Phone 7

This TechNet article on Windows Phone 7 got my attention. It appears you cannot fully utilize Exchange ActiveSync mailbox policies, unless you set AllowNonProvisionableDevices to True. If you don’t do that, you can only use the following properties, otherwise synchronization issues might be experienced:

  • PasswordRequired
  • MinPasswordLength
  • IdleTimeoutFrequencyValue
  • DeviceWipeThreshold
  • AllowSimplePassword
  • PasswordExpiration
  • PasswordHistory
  • DisableRemovableStorage
  • DisableIrDA
  • DisableDesktopSync
  • BlockRemoteDesktop
  • BlockInternetSharing

Another option is to create a seperate policy for Windows Phone 7 users.

Another thing worth mentioning is that when using multiple Exchange accounts on your Windows Phone 7, policies will be merged into a most restrictive set (credit to Dave Stork who got the information at TEE10).

Exchange ActiveSync and Hotmail

As of Monday, it is possible to synchronise your Hotmail account, i.e. e-mail, calendar and contacts, with your mobile using Exchange ActiveSync (EAS).

To synchronise your mobile with Hotmail, use the following settings:

Server m.hotmail.com
Username E-mail address, e.g. jandvries@hotmail.com
Password *****
Domain Leave blank
SSL Enabled

When asked, choose to accept the SSL certificate.

Synchronisation currently works for Windows Mobile 6.x, Windows Phone 7, iPhone, iPod Touch, iPad and Nokia E/S/N-Series with Mail for Exchange.

iOS 4.0.1 fixes ActiveSync issues

Apple published an update for iOS4 – iOS 4.0.1 – which should fix the synchronization issues between iPhone users using iOS4 and Exchange Server.

The issue was discovered after Apple released iOS 4.0, after which many people reported issues syncing their updated iPhone 4, iPhone 3G, 3GS or iPod Touch devices with Exchange. Initially Apple released a workaround in the form of a configuration profile which increased timeout values to 240 seconds, instead of 30. Note that iOS 4.0.1 also sets the timeout to 240 seconds as the new default.

You can view the support article (ts3398) here.

Windows Phone 7 to support multiple Exchange accounts

I seem to have missed the news from a few days back that during a broadcast on the @ch9live development network , Joe Belfiore, Microsoft Corporate Vice President for Windows Mobile, confirmed multiple Exchange account support in Windows Phone 7 Series. Goodbye to unsupported hacks or POP/IMAP’ing those additional Exchange boxes. I assume includes all the additional benefits like Direct Push (hello battery life!).

In addition, Belfiore stated that on Windows Phone 7 various calendars will be displayed in a single view using coler coding to differentiate between the calendars (i.e. accounts).

Thanks to fellow Exchange guy Magnus Björk for spotting this one.