struct message_str
{
    Message*  next; // For kernel use only.

~~~途中省略~~~

    int headerProtocols[MAX_HEADERS];
    int headerSizes[MAX_HEADERS];

    // Users should not modify anything above this line.

    // 転送時に自身のIPアドレスを設定するためのフィールド
    NodeAddress last_forwarder_ip;
};

12817 void
12818 RouteThePacketUsingLookupTable(Node *node, Message *msg, int incomingInterface)
12819 {
12820     NetworkDataIp *ip = (NetworkDataIp *) node->networkData.networkVar;
12821     IpHeaderType *ipHeader = (IpHeaderType *) msg->packet;
12822 
12823     int outgoingInterface;
12824     NodeAddress nextHop;
+++++     int testIncomingInterface;
+++++     NodeAddress testPreviousHop;
12825 
12826     NetworkGetInterfaceAndNextHopFromForwardingTable(
12827         node, ipHeader->ip_dst, &outgoingInterface, &nextHop);
+++++     NetworkGetInterfaceAndNextHopFromForwardingTable(
+++++         node, ipHeader->ip_src, &testIncomingInterface, &testPreviousHop);