摘要 |
A communication system includes a server and a router which are both connected to a first network. The server grants to a response packet destined for an anycast address sent from a communication apparatus connected to a second network, anycast address option information indicating that an anycast address of a sender of the response packet, puts a signature field for a setting of an electronic signature in the response packet; and transmits to the communication apparatus the response packet. The router receives the response packet, validates whether the response packet is sent from a legitimate server based on the anycast address option information if the response packet includes the anycast address option information. The router also sets an electronic signature based on information related with the response packet in the signature field if the response packet is sent from the legitimate server, and transmits the response packet.
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