So because of the way active directory handles Group Policy I have been tasked with finding out why this is failing over the WAN. Basically I know why, but don't know how to correct it. I am trying to increase the MTU over an ipsec tunnel to 2048 to allow Microsoft Slowlink detection to occur. http://support.microsoft.com/kb/227260 . Basically, it sends 2 icmp packets. One at a normal size and one at a size of 2048. In my case this is trying to occur over an ipsec tunnel and failing due to the MTU being at 1440. I have seen a few articles about increasing it to 1500, but is there a way to increase the MTU to allow the 2048 sized icmp packets?