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Usage guidelines
IPsec supports the following encapsulation modes:
•
Transport mode —The security protocols protect the upper layer data of an IP packet. Only the
transport layer data is used to calculate the security protocol headers. The calculated security
protocol headers and the encrypted data (only for ESP encapsulation) are placed after the
original IP header. You can use the transport mode when end-to-end security protection is
required (the secured transmission start and end points are the actual start and end points of
the data). The transport mode is typically used for protecting host-to-host communications.
•
Tunnel mode —The security protocols protect the entire IP packet. The entire IP packet is used
to calculate the security protocol headers. The calculated security protocol headers and the
encrypted data (only for ESP encapsulation) are encapsulated in a new IP packet. In this mode,
the encapsulated packet has two IP headers. The inner IP header is the original IP header. The
outer IP header is added by the network device that provides the IPsec service. You must use
the tunnel mode when the secured transmission start and end points are not the actual start and
end points of the data packets (for example, when two gateways provide IPsec but the data
start and end points are two hosts behind the gateways). The tunnel mode is typically used for
protecting gateway-to-gateway communications.
The IPsec transform sets at both ends of the IPsec tunnel must have the same encapsulation mode.
Examples
# Configure IPsec transform set tran1 to use the transport mode for IP packet encapsulation.
<Sysname> system-view
[Sysname] ipsec transform-set tran1
[Sysname-ipsec-transform-set-tran1] encapsulation-mode transport
Related commands
ipsec transform-set
esn enable
Use esn enable to enable the Extended Sequence Number (ESN) feature.
Use
undo esn enable
to disable the ESN feature.
Syntax
esn enable [ both ]
undo esn enable
Default
The ESN feature is disabled.
Views
IPsec transform set view
Predefined user roles
network-admin
Parameters
both : Specifies IPsec to support both extended sequence number and traditional sequence number.
If you do not specify this keyword, IPsec only supports extended sequence number.
Usage guidelines
The ESN feature extends the sequence number length from 32 bits to 64 bits. This feature prevents
the sequence number space from being exhausted when large volumes of data are transmitted at