网络专题训练Ipv4转发实验报告.doc

网络专题训练Ipv4转发实验报告一、 实验目的1. 了解路由器是如何为分组选择路由，并逐跳地将分组发送到目的主机。2. 初步接触路由表这一数据结构，认识路由器是如何根据路由表确定分组转发的下一跳。二、 实验要求1. 设计路由表的数据结构。2. 完成对Ipv4分组的接受和发送。3. 完成对Ipv4分租的转发。三、 实验基本框架1. 路由初始化函数 void stud_Route_Init()2. 路由添加函数 void stud_route_add(stud_route_msg*proute)3. 路由信息结构体头部包含路由表项目的地址，掩码长度和下一跳的信息4. 转发处理函数int stud_fwd_deal(char* pBuffer, int length)5. 本地处理函数void fwd_LocalRcv(char* pBuffer, int length)6. 下层发送函数void fwd_SendtoLower(char* pBuffer, int length, unsigned int nexthop)7. 丢弃分组函数void fwd_DiscardPkt(char* pBuffer, int type)8. 获取本机地址函数UINT32 getIpv4Address()四、 设计思路首先设计路由表项结构struct routeTableItemunsigned int destIP; /目的地址IPunsigned int mask; /掩码，用于取出对应的网络地址unsigned int masklen; /掩码长度，用于实现最长匹配unsigned int nexthop; /下一跳地址;vector m_table /存储路由表然后，在路由表项添加函数中，处理路由表项的添加void stud_route_add(stud_route_msg *proute)routeTableItem newTableItem;newTableItem.masklen = ntohl(proute-masklen);/记录掩码长度newTableItem.mask = (1(ntohl(proute-masklen)-1);/获得掩码newTableItem.destIP = ntohl(proute-dest)&newTableItem.mask;/获取网路地址段newTableItem.nexthop = ntohl(proute-nexthop);/获取下一条m_table.push_back(newTableItem);/加入路由表return;每当收到一个新的包时首先读取包头信息/获取包头信息int IHL = pBuffer0 & 0xf; /获取包头长度（bits/32）/cout IHL: IHL endl;int TTL = (int)pBuffer8; /timetolive, 存活时间int headerChecksum = ntohl(*(unsigned short*)(pBuffer+10);/头部校验和int destIP = ntohl(*(unsigned int*)(pBuffer+16);/目的地址然后判断此包是否是发给本机的if(destIP = getIpv4Address()fwd_LocalRcv(pBuffer, length);return 0;判断是否应该丢弃此包if(TTL = 0)fwd_DiscardPkt(pBuffer, STUD_FORWARD_TEST_TTLERROR);return 1;查找最长匹配for(int i = 0; i longestMatchLen & m_tablei.destIP = (destIP & m_tablei.mask)bestMatch = i;isMatch = true;longestMatchLen = m_tablei.masklen;查找成功，重新计算校验和并发送if(isMatch)char *buffer = new charlength; memcpy(buffer,pBuffer,length); buffer8-; /TTL - 1int sum = 0; /重新计算校验和 unsigned short int localCheckSum = 0; for(int j = 0; j 2 * IHL; j +) if (j = 5)continue; sum = sum + (bufferj*2 16) != 0)sum = unsigned(sum) 16 + sum & 0xffff; localCheckSum = htons(0xffff - (unsigned short int)sum);memcpy(buffer+10, &localCheckSum, sizeof(unsigned short);/发送fwd_SendtoLower(buffer, length, m_tablebestMatch.nexthop);return 0;查找不成功，丢弃该包elsefwd_DiscardPkt(pBuffer, STUD_FORWARD_TEST_NOROUTE);return 1;五、 收获1. 对Ipv4的转发机制有了实际的认识和体会2. 实践了最长匹配算法六、 源代码/* THIS FILE IS FOR IP FORWARD TEST*/#include sysInclude.h#include using std:vector;#include using std:cout;/ system supportextern void fwd_LocalRcv(char *pBuffer, int length);extern void fwd_SendtoLower(char *pBuffer, int length, unsigned int nexthop);extern void fwd_DiscardPkt(char *pBuffer, int type);extern unsigned int getIpv4Address( );/ implemented by studentsstruct routeTableItemunsigned int destIP;unsigned int mask;unsigned int masklen;unsigned int nexthop;vector m_table;void stud_Route_Init()m_table.clear();return;void stud_route_add(stud_route_msg *proute)routeTableItem newTableItem;newTableItem.masklen = ntohl(proute-masklen);newTableItem.mask = (1(ntohl(proute-masklen)-1);newTableItem.destIP = ntohl(proute-dest)&newTableItem.mask;newTableItem.nexthop = ntohl(proute-nexthop);m_table.push_back(newTableItem);return;int stud_fwd_deal(char *pBuffer, int length)int IHL = pBuffer0 & 0xf; int TTL = (int)pBuffer8; int headerChecksum = ntohl(*(unsigned short*)(pBuffer+10);int destIP = ntohl(*(unsigned int*)(pBuffer+16);if(destIP = getIpv4Address()fwd_LocalRcv(pBuffer, length);return 0;if(TTL = 0)fwd_DiscardPkt(pBuffer, STUD_FORWARD_TEST_TTLERROR);return 1;bool isMatch = false;unsigned int longestMatchLen = 0;int bestMatch = 0;for(int i = 0; i longestMatchLen & m_tablei.destIP = (destIP & m_tablei.mask)bestMatch = i;isMatch = true;longestMatchLen = m_tablei.masklen;/cout find one endl;if(isMatch)char *buffer = new charlength; memcpy(buffer,pBuffer,length); buffer8-; /TTL - 1int sum = 0; unsigned short int localCheckSum = 0; for(int j = 0; j 2 * IHL; j +) if (j = 5)continue; sum = sum + (bufferj*2 16) != 0)sum = unsigned(sum) 16 + sum & 0xffff; localCheckSum = htons(0xffff - (unsigned shor