If you configure both IPsec and QoS on an interface, make sure the IPsec traffic classification rules match
the QoS traffic classification rules. If the rules do not match, QoS might classify the packets of one IPsec SA
to different queues, causing packets to be sent out of order. When IPsec anti-replay is enabled, IPsec will
drop the incoming packets that are out of the anti-replay window, resulting in packet loss.
IPsec traffic classification rules are determined by the referenced ACL rules. For information about QoS
classification rules, see
IP Security (IPsec) is defined by the IETF to provide interoperable, high-quality, cryptographically-based
security for IP communications. It is a Layer 3 VPN technology that transmits data in a secure channel
established between two endpoints (such as two security gateways). Such a secure channel is usually
called an IPsec tunnel.
IPsec is a security framework that comprises a set of protocols, including Authentication Header (AH),
Encapsulating Security Payload (ESP), Internet Key Exchange (IKE), and algorithms for authentication
and encryption. AH and ESP are security protocols that provide security services. IKE performs automatic
IPsec provides the following security services for data packets in the IP layer:
Confidentiality—The sender encrypts packets before transmitting them over the Internet, protecting
the packets from being eavesdropped en route.
Data integrity—The receiver verifies the packets received from the sender to make sure they are not
tampered with during transmission.
Data origin authentication—The receiver verifies the authenticity of the sender.
Anti-replay—The receiver examines packets and drops outdated and duplicate packets.
IPsec delivers the following benefits:
Reduced key negotiation overhead and simplified maintenance by supporting the IKE protocol. IKE
provides automatic key negotiation and automatic IPsec security association (SA) setup and
Good compatibility. You can apply IPsec to all IP-based application systems and services without
Encryption on a per-packet rather than per-flow basis. Per-packet encryption allows for flexibility
and greatly enhances IP security.
Security protocols and encapsulation modes
IPsec comes with two security protocols, AH and ESP. They define how to encapsulate IP packets and the
security services that they can provide.
ACL and QoS Configuration Guide