Hash and URL Certificate Exchange

IKEv2 supports Hash and URL Certificate Exchange, which is used during an IKEv2 negotiation of an SA. You store the certificate on an HTTP server, which is specified by a URL. The peer fetches the certificate from the server based on receiving the URL to the server. The hash is used to check whether the content of the certificate is valid or not. Thus, the two peers exchange certificates with the HTTP CA rather than with each other.
The hash part of Hash and URL reduces the message size and thus Hash and URL is a way to reduce the likelihood of packet fragmentation during IKE negotiation. The peer receives the certificate and hash that it expects, and thus IKE Phase 1 has validated the peer. Reducing fragmentation occurrences helps protect against DoS attacks.
You can enable the Hash and URL certificate exchange when configuring an IKE gateway by selecting HTTP Certificate Exchange and entering the Certificate URL. The peer must also use Hash and URL certificate exchange in order for the exchange to be successful. If the peer cannot use Hash and URL, X.509 certificates are exchanged similarly to how they are exchanged in IKEv1.
If you enable the Hash and URL certificate exchange, you must export your certificate to the certificate server if it is not already there. When you export the certificate, the file format should be Binary Encoded Certificate (DER). See Export a Certificate for a Peer to Access Using Hash and URL.

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