计算机网络概论上机实习ipv4协议转发实验

IPv4分组收发实验的基础上增IPv4分组，根据其信息进行如下几类处理():externvoidexternvoidfwd_DiscardPkt(char∗pBuffer,inttype)externexternvoidfwd_SendtoLower(char∗pBuffer,intlength,unsigned其中，pBufferIPv4数据包的指针；length(+内容)，以字节计；nexthop是转发的下一跳地址。fwd_LocalRev:将IPexternexternvoidfwd_LocalRev(char∗pBuffer,intlength)其中，pBufferIPv4数据包的指针，length是数据包总长度，以字节typedefstructstud_route_msg{typedefstructstud_route_msg{unsignedintdest;unsignedintmaxlen;unsignedint2345表条目。此处采用C++STL中的map容器，其本身由一种平衡检索二叉树树map<map<int,int>下一跳地址nexthop。ࡓခौinsert()方法将其路由表中。条目，则调用fwd_DiscardPkt()抛弃该包。校验和的计算方法与前次实验相同。需要注意的是，由于重新计算校验和，需把原校验和字段，再对整个报头计算校验和。如果将原校验和字段也加入，网络字节序的；而本机获取的地址及路由表项内容是以主机字节序的。)目等错误，函数返回1。在本次实习中，对IPv4协议的转发流程细节更加熟悉，对路由表数SectionSection lude lude usingstd::map;externvoidfwd_LocalRcv(char∗pBuffer,intlength)externvoidfwd_SendtoLower(char∗pBuffer,intlength,unsignedintexternvoidfwd_DiscardPkt(char∗pBuffer,inttype)externunsignedintgetIpv4Address()/∗RouteTable<DstAddr,nexthop>map<int,int> theRouteTablevoidstud_Route_Init/∗AddinganewentrytotheRouteTablevoidstud_route_add(stud_route_msgintDstAddr=(ntohl(proute−>dest))&(0xFFFFFFFF<<(32−htonl(proute−>intnexthop=ntohl(RouteTable.insert(pair<int,int>(DstAddr,nexthop))/∗Dealingwiththereceptionandforwardingintstud_fwd_deal(char∗pBuffer,intlengthintIHL=pBuffer[0]&intTTL=(int)pBufferintDstAddr=ntohl(∗(unsigned∗)(&pBuffer[16]))/∗Thishostisthedestination,sendtotheupperclassif(DstAddr23456789return}/∗TimeOut,discardingthepacket(TTL<=fwd_DiscardPkt(pBuffer,return}/∗SearchtheDstAddrintheRouteTablemap<int,int>::i iter=RouteTable.find/∗DstnotfoundintheRouteTable,discardingthepacket(iter==fwd_DiscardPkt(pBuffer,return}/∗Routerforwardingthepacketchar∗buffer=newchar[lengthmemcpy(buffer,pBuffer,length)/∗TTL−1buffer[8]=(char)(TTL−/∗CalculatingandfillingintheHeaderChecksumunsignedintHeaderCheckSum=memset(&buffer[10],0,sizeof(short))for(inti=0;i<4∗IHL;i+=HeaderCheckSum+=((buffer[i]&0xFF)<<8)+(buffer[i+1]&HeaderCheckSum+=(HeaderCheckSum>>HeaderCheckSum=buffer[10]=(char)((unsignedshort)HeaderCheckSum>>buffer[11]=(char)((unsignedshort)HeaderCheckSum&/∗Forwardingfwd_SendtoLower(buffer,length,(∗iter).return}

return/∗TimeOut,discardingthepacket77

if(TTL<=fwd_DiscardPkt(pBuffer,return}/∗SearchtheDstAddrintheRouteTablemap<int,int>:: iter=RouteTable.find/∗DstnotfoundintheRouteTable,discardingthepacketif(iter==fwd_DiscardPkt(pBuffer,return}/∗Routerforwardingthepacket∗/char∗buffer=newchar[length];memcpy(buffer,pBuffer,length);/∗TTL−1buffer[8]=(char)(TTL−/∗CalculatingandfillingintheHeaderChecksum∗/unsignedintHeaderCheckSum=0;memset(&buffer[10],0,sizeof(short));for(inti=0;i<4∗IHL;i+=HeaderCheckSum+=((buffer[i]&0xFF)<<8)+(buffer[i+1]&0xFF);HeaderCheckSum+=(HeaderCheckSum>>16);HeaderCheckSum=buffer[10]=(char)