Information About Source Interface Selection for Outgoing Traffic with Certificate Authority
Certificates That Identify an Entity
Certificates can be used to identify an entity. A trusted server, known as the certification authority (CA), issues the certificate to the entity after determining the identity of the entity. A device that is running Cisco IOS XE software obtains its certificate by making a network connection to the CA. Using the Simple Certificate Enrollment Protocol (SCEP), the device transmits its certificate request to the CA and receives the granted certificate. The device obtains the certificate of the CA in the same manner using SCEP. When validating a certificate from a remote device, the device may again contact the CA or a Lightweight Directory Access Protocol (LDAP) or HTTP server to determine whether the certificate of the remote device has been revoked. (This process is known as checking the certificate revocation list [CRL].)
In some configurations, the device may make the outgoing TCP connection using an interface that does not have a valid or IP address that can be routed. The user must specify that the address of a different interface be used as the source IP address for the outgoing connection. Cable modems are a specific example of this requirement because the outgoing cable interface (the RF interface) usually does not have an IP address that can be routed. However, the user interface (usually Ethernet) does have a valid IP address.
Source Interface for Outgoing TCP Connections Associated with a Trustpoint
The crypto ca trustpoint command is used to specify a trustpoint. The source interface command is used along with the crypto ca trustpoint command to specify the address of the interface that is to be used as the source address for all outgoing TCP connections associated with that trustpoint.
If the interface address is not specified using the source interface command, the address of the outgoing interface is used.