If you 're facing troubles with clients connecting to VPN and can't resolve DNS please check the following
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCuz27826/?rfs=qvred
In short
Anyconnect creates a static route on the client for the DHCP server. if your DHCP server also servers as DNS etc. this breaks the DNS resolution for your client.
Apply the following as workaround
group-policy DfltGrpPolicy attributes
webvpn
anyconnect-custom-attr no-dhcp-server-route
anyconnect-custom-data no-dhcp-server-route no-dhcp-server-route true
group-policy <XXX> attributes
anyconnect-custom no-dhcp-server-route value no-dhcp-server-route
