Message sending

A network device, comprising:

• a processor;
• a transceiver;
• a machine-readable storage medium storing machine executable instructions that can be executed by the processor and cause the processor to implement the following steps:
• receiving, by the transceiver, a first service message, which comprises a destination address, a first in-situ flow detection option, a segment routing header (SRH) and an original service message, wherein the SRH comprises an SID list indicating a forwarding path, the first in-situ flow detection option is used to determine whether the first service message is sent on the forwarding path, or is replicated to obtain a second service message;
• if the destination address is a locally configured proxy SID, sending, by the transceiver, the second service message on the forwarding path and the original service message to a service function node;
• wherein, the second service message comprises a second in-situ flow detection option, which comprises replication flag information for indicating that the second service message is a replication message of the first service message.