3Com Switch 8800 Advanced Software V5 Configuration Guide

Introduction to Tunneling 379
■ If the source IP address of the tunnel packet matches the expedite termination
subnet, the packet is sent to the IPv6 switch fabric to forward or sent to the
CPU for processing.
■ If the tunnel packet needs to be forwarded, the IPv6 switch fabric decapsulates
the tunnel packet to obtain the original IPv6 packet and then forwards it
directly.
The expedite termination function solves the problem that the rate of tunnel
packets is restricted by the loopback port in the tunnel service.
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With expedite termination enabled, IPv6 packets to be encapsulated still need to
be sent to the service loopback port for processing.
Tunnel hybrid insertion
In practice, many cards only support IPv4. However, a tunnel can only be
established over IPv6 cards. After tunnel packets arrive on the destination node, it
is very likely that an IPv4 card received the packets. The tunnel hybrid insertion
function enables IPv4 cards to support the tunnel termination. Through the
function, tunnel packets can be terminated without obstruction on the destination
node. This function is implemented by configuring an ACL on incoming interfaces
of IPv4 cards to redirect tunnel packets to IPv6 cards.
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CAUTION: In the case of tunnel hybrid insertion, the outbound interface of tunnel
packets must support IPv6 if expedite termination is enabled. Otherwise, tunnel
packets cannot be encapsulated or decapsulated.
IPv4 over IPv4 Tunnel Introduction to IPv4 over IPv4 tunneling protocol
IPv4 over IPv4 tunneling protocol (RFC 1853) is developed for IP data packet
encapsulation so that data can be transferred from one IPv4 network to another
IPv4 network.
Encapsulation and decapsulation
Packets to be transferred through a tunnel undergo an encapsulation process and
decapsulation process.
Figure 115 shows these two processes.
Figure 115 Principle of IPv4 over IPv4 tunnel
Router A Router B
IPv 4 host
IPv4 network
IPv4 tunnel
IPv 4 network
IPv 4 host
IPv4 network
IPv 4 header IPv4 data
IPv 4 header IPv4 dataIPv 4 header
IPv4 header IPv4 data