R3303-HP HSR6800 Routers Security Configuration Guide

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IPsec tunnel interface
An IPsec tunnel interface is a Layer 3 logical interface. It supports dynamic routing. All packets including
multicast packets that are routed to an IPsec tunnel interface are IPsec protected.
The IPsec tunnel interface has the following advantages:
• Simplified configuration—The IPsec tunnel interface is easier to configure compared to using
access control lists (ACLs) to identify protected packets. The IPsec tunnel interface improves network
scalability and reduces maintenance costs.
• Reduced payload—The IPsec tunnel interface requires less protocol costs and uses less bandwidth
than IPsec over GRE and IPsec over L2TP, which require a GRE header or L2TP header to be added
to each packet.
• Flexible service application—You can apply a service such as NAT or QoS to packets before or
after they are encrypted by IPsec. To handle packets prior to IPsec encryption, apply the service to
the IPsec tunnel interface. To handle IPsec encrypted packets, apply the service to the physical
outbound interface.
Operation of the IPsec tunnel interface
IPsec encapsulation and de-encapsulation occur on IPsec tunnel interfaces. Figure 85 shows how a clear
text packet arriving at a router is forwarded to the IPsec tunnel interface, encapsulated, and forwarded
out.
Figure 85 Encapsulation process of a clear text packet
1. The router forwards a clear text packet received on the inbound interface to the forwarding
module.
2. The forwarding module looks up the routing table and, if the packet must be IPsec protected,
forwards the packet to the IPsec tunnel interface. The original IP packet is encapsulated into to form
a new IP packet. The source and destination of the new packet are respectively the source and
destination address of the tunnel interface.
3. The IPsec tunnel interface encapsulates the packet, and then sends the packet to the forwarding
module.
4. The forwarding module looks up the routing table again and forwards the IPsec-encrypted packet
out of the physical outbound interface that is associated with the tunnel interface.
Figure 86 sho
ws how an IPsec packet is de-encapsulated on an IPsec tunnel interface.
Inbound
interface
Forwarding
Outbound
interface
Encryption
IPsec virtual
tunnel interface
(1)
(2)
(3)
(4)
IPsec tunnel
Router
Clear text
packets
Encrypted
packets
Inbound
Outbound