> # Crypto IPv4-ACL Guidelines

> Follow these guidelines when configuring IPv4-ACLs for the IPsec feature:

> - The Cisco NX-OS software only allows name-based IPv4-ACLs.
> - When an IPv4-ACL is applied to a crypto map, the following options apply:
> - Permit—Applies the IPsec feature to the traffic.
> - Deny—Allows clear text (default).

> Note IKE traffic (UDP port 500) is implicitly transmitted in clear text.

> - The IPsec feature only considers the source and destination IPv4 addresses and subnet masks, protocol, and single port number. There is no support for IPv6 in IPsec.

> Note The IPsec feature does not support port number ranges and ignores higher port number field, if specified.

> - The permit option causes all IP traffic that matches the specified conditions to be protected by crypto, using the policy described by the corresponding crypto map entry.
> - The deny option prevents traffic from being protected by crypto. The first deny statement causes the traffic to be in clear text.
> - The crypto IPv4-ACL you define is applied to an interface after you define the corresponding crypto map entry and apply the crypto map set to the interface.
> - Different IPv4-ACLs must be used in different entries of the same crypto map set.
> - Inbound and outbound traffic is evaluated against the same outbound IPv4-ACL. Therefore, the IPv4-ACL's criteria is applied in the forward direction to traffic exiting your switch, and the reverse direction to traffic entering your switch.
> - Each IPv4-ACL filter assigned to the crypto map entry is equivalent to one security policy entry. The IPsec feature supports up to 120 security policy entries for each MPS-14/2 module and Cisco MDS 9216i Switch.
> - IPsec protection is applied to traffic between switch interface S0 (IPv4 address 10.0.0.1) and switch interface S1 (IPv4 address 20.0.0.2) as the data exits switch A's S0 interface enroute to switch interface S1. For traffic from 10.0.0.1 to 20.0.0.2, the IPv4-ACL entry on switch A is evaluated as follows:
> - source = IPv4 address 10.0.0.1
> - dest = IPv4 address 20.0.0.2

> For traffic from 20.0.0.2 to 10.0.0.1, that same IPv4-ACL entry on switch A is evaluated as follows:

> - source = IPv4 address 20.0.0.2
> - dest = IPv4 address 10.0.0.1
> - If you configure multiple statements for a given crypto IPv4-ACL that is used for IPsec, the first permit statement that is matched is used to determine the scope of the IPsec SA. Later, if traffic matches a different permit statement of the crypto IPv4-ACL, a new, separate IPsec SA is negotiated to protect traffic matching the newly matched IPv4-ACL statement.
> - Unprotected inbound traffic that matches a permit entry in the crypto IPv4-ACL for a crypto map entry flagged as IPsec is dropped, because this traffic was expected to be protected by IPsec.
> - For IPsec to interoperate effectively with Microsoft iSCSI initiators, specify the TCP protocol and the local iSCSI TCP port number (default 3260) in the IPv4-ACL. This configuration ensures the speedy recovery of encrypted iSCSI sessions following disruptions such as Gigabit Ethernet interfaces shutdowns, VRRP switchovers, and port failures.

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