Cisco's proprietary AnyConnect clients and servers were originally built against a patched, 2007 release of OpenSSL 0.9.8f, which implemented a pre-release version of DTLS that was not compatible with DTLS 1.0 as standardized in RFC 4347. Because of this, it was difficult to make OpenConnect implement a Cisco-compatible version of DTLS without linking against OpenSSL.
