# xv6 network-net 3 最近土法煉鋼完成三方交握的部分，沒錯這個實驗還在繼續，為了證明最初的概念是對的。 # server 我們要完成的是三方交握的第一階段，也就是 bind - listening - accept 能不能節省掉這個步驟是可以的 ![](https://i.imgur.com/3T3N11T.png) ![](https://i.imgur.com/fJ53VR4.png) 當我把sockecvudp while 迴圈裡 if判斷是拿掉的當下就是變成所有流量只要有socket 監聽就可以直接回傳。 # tcp header ![](https://i.imgur.com/cWDGkCw.png) 目前就已經整合進修改過後的xv6 kernel 可以對一般的socket 進行到三方交握階段， # multi-network card qemu tap 透過這些設定，可以讓我們的xv6 支援更多張網卡 ```bahs ip tuntap add mode tap name tap0 ip addr add 172.16.100.1/24 dev tap0 ip link set tap0 up ``` ```makefile # QEMUOPTS += -netdev user,id=net0,hostfwd=udp::$(FWDPORT)-:2000,hostfwd=tcp::7-:7 -object filter-dump,id=net0,netdev=net0,file=packets.pcap # QEMUOPTS += -device e1000,netdev=net0,bus=pcie.0 QEMUOPTS += -netdev tap,id=net1,ifname=tap0 -object filter-dump,id=net1,netdev=net1,file=packets2.pcap QEMUOPTS += -device e1000,netdev=net1 ``` ![](https://i.imgur.com/Tp615Sa.png) # debug checksuming 最主要的部份如果真的要實現一個tcp 協議需要對封包處理很熟悉，如果有多張網卡的情況可以透過下列指令關閉網卡的checksum 驗證，不然你的封包會莫名其妙地消失 ethtool -K ethx tx off rx off 下列網卡就是針對 tap0 但是可以看到 他寫的是fixed (有關等於沒關 ![](https://i.imgur.com/0JQsRmO.png) 下列是出現封包遺失階段的畫面，網路上資料非常少 ![](https://i.imgur.com/EUiMoZd.png) server 可以看到有發送syn/ack 但是client遲遲不能解析封包 沒有gui介面可以透過 ```bash= sudo tcpdump -i tap0 -nn tcp ``` 我找了一個https://github.com/pandax381/xv6-net 虛擬機可以研究了一段時間，稍微研究了他的封包之間的協議可以發現上方是對方的封包訊息，下方是我的 ![](https://i.imgur.com/krvMnEW.png) ![](https://i.imgur.com/Q7lPY5E.png) 透過 ```bash= netstat --statistics --tcp ``` ![](https://i.imgur.com/PympDTq.png) 可以看到我們的封包 被網卡拋棄了! 在檢查碼的這部分我發現我的檢查碼每次算會跟真實checksuming 差 ```c= uint16 tmp = 0x4fb; ``` 開啟wireshark 可以看到封包checksum狀況 ![](https://i.imgur.com/od6vCiN.png) 這是錯誤範例 ![](https://i.imgur.com/wAoMAYG.png) 後面還有異動幾個版本，最後結論就是 最後懶得改了直接 答案-4fb ```c= static void net_rx_udp(struct mbuf *m, uint16 len, struct ip *iphdr) { struct tcp *udphdr, *udphdr2; uint16 src; uint16 dst; uint32 tmp, seq; uint8 flg; uint8 flg2; uint8 dst1; uint8 dst2; uint8 dst3; uint8 dst4; uint32 ack; // uint32 sip; uint16 sport, dport; printf("test16\n"); struct mbuf *m2; m2 = mbufalloc(MBUF_DEFAULT_HEADROOM); udphdr = mbufpullhdr(m, *udphdr); udphdr2 = mbufpushhdr(m2, (*udphdr2)); if (!udphdr) goto fail; printf("pre recv\n"); // // TODO: validate UDP checksum // // validate lengths reported in headers // if (ntohs(udphdr->ulen) != len) // goto fail; // len -= sizeof(*udphdr); // if (len > m->len) // goto fail; // // minimum packet size could be larger than the payload // mbuftrim(m, m->len - len); // printf("test14\n"); // // parse the necessary fields src = ntohl(iphdr->ip_src); tmp = udphdr->dst; udphdr->dst = udphdr->src; udphdr->src = tmp; udphdr2->src = udphdr->dst; udphdr2->dst = udphdr->src; // udphdr2->src = udphdr->dst; // udphdr2->dst = udphdr->src; // udphdr2->seq = 0; // udphdr2->ack = 0; // udphdr2->off = 0; // udphdr2->win = 0; // udphdr2->sum = 0; // udphdr2->urg =0; // uint16 src; // uint16 dst; // uint32 seq; // uint32 ack; // uint8 off; // uint8 flg; // uint16 win; // uint16 sum; // uint16 urg; dst = ntohs(udphdr->dst); seq = udphdr->seq; flg = udphdr->flg; flg2 = 18; dst = (iphdr->ip_src << 24) | (iphdr->ip_src << 16) | (iphdr->ip_src << 8) | (iphdr->ip_src << 0); dst1 = (iphdr->ip_src >> 24); dst2 = (iphdr->ip_src >> 16); dst3 = (iphdr->ip_src >> 8); dst4 = (iphdr->ip_src >> 0); ack = udphdr->ack; // | (0 << 16) | (2 << 8) | (2 << 0); printf("dst%u\n", dst); printf("src%u\n", src); // printf("dst %u\n", udphdr->dst); printf("src%d\n", ntohs(udphdr->src)); printf("dst %d\n", ntohs(udphdr->dst)); printf("seq %u\n", ntohl(seq)); printBits(flg); printBits(flg2); printf("flg %d\n", flg); printf("flg2 %d\n", flg2); printf("addr4 %d\n", dst4); printf("addr3 %d\n", dst3); printf("addr2 %d\n", dst2); printf("addr1 %d\n", dst1); dst1 = (iphdr->ip_dst >> 24); dst2 = (iphdr->ip_dst >> 16); dst3 = (iphdr->ip_dst >> 8); dst4 = (iphdr->ip_dst >> 0); printf("addr4 %d\n", dst4); printf("addr3 %d\n", dst3); printf("addr2 %d\n", dst2); printf("addr1 %d\n", dst1); printf("ack %u\n", ntohl(ack)); printf("seq ntohs %u\n", ntohs(seq) + 1); printf("seq ntohl %u\n", ntohl(seq) + 1); udphdr->flg = flg2; if (stseq == 0) { udphdr->seq = htonl(ntohl(seq) + 99); } else { udphdr->seq = htonl(ntohl(stseq) + 1); stseq = ntohl(stseq) + 1; } // 172.17.35.175 // tmp = (192 << 24) | (168<< 16) | (100<< 8) | (1 << 0); udphdr2->src = udphdr->src; udphdr2->dst = udphdr->dst; udphdr2->ack = htonl(ntohl(seq) + 1); udphdr2->seq = htonl(ntohl(seq) + 123123123); udphdr2->flg = flg2; udphdr2->off = (sizeof(struct tcp) >> 2) << 4; udphdr2->win = udphdr->win; udphdr2->sum = 0; udphdr2->urg = 0; // udphdr2->option = udphdr->option; uint32 pseudo = 0; // tmp = (172 << 24) | (16 << 16) | (100 << 8) | (2 << 0); // tmp = (10 << 24) | (0 << 16) | (2 << 8) | (15 << 0); pseudo += ((local_ip) >> 16) & 0xffff; pseudo += (local_ip)&0xffff; // tmp = (172 << 24) | (16 << 16) | (100 << 8) | (1 << 0); tmp = (172 << 24) | (16 << 16) | (100 << 8) | (1 << 0); pseudo += (tmp >> 16) & 0xffff; pseudo += tmp & 0xffff; pseudo += htons((uint16)IP_PROTOCOL_TCP); pseudo += htons(sizeof(struct tcp)); uint16 tmp2 = 0x4fb; printf("%u\n", tmp2); // udphdr2->sum =cksum16((uint16 *)udphdr2, sizeof(struct tcp), pseudo); udphdr2->sum = cksum16((uint16 *)udphdr2, sizeof(struct tcp), pseudo); printf("%u\n", udphdr2->sum); printf("%u\n", udphdr2->sum + tmp2); printf("%u\n", htons(udphdr2->sum)); printf("%u\n", htons(tmp2)); printf("%u\n", htons(udphdr2->sum) + tmp2); udphdr2->sum = htons(htons(udphdr2->sum) + tmp2); printf("%u\n", htons(udphdr2->sum) + htons(tmp2)); uint32 pseudo2 = 0; // tmp = (172 << 24) | (16 << 16) | (100 << 8) | (2 << 0); // tmp = (10 << 24) | (0 << 16) | (2 << 8) | (15 << 0); pseudo2 += (local_ip) >> 16; pseudo2 += (local_ip)&0xffff; // tmp = (172 << 24) | (16 << 16) | (100 << 8) | (1 << 0); // 3 0.005475 172.29.64.1 10.0.2.15 TCP 58 58866 → 11111 [SYN] Seq=0 Win=65535 Len=0 MSS=1460 tmp = (172 << 24) | (16 << 16) | (100 << 8) | (1 << 0); pseudo2 += tmp >> 16; pseudo2 += tmp & 0xffff; pseudo2 += htons((uint16)IP_PROTOCOL_TCP); pseudo2 += htons(sizeof(struct tcp)); // in_cksum() if (cksum16((uint16 *)udphdr2, sizeof(struct tcp), pseudo2) != 0) { printf("tcp checksum error!\n"); } else printf("tcp checksum ok!\n"); // mbuftrim(m2,4) printf("%x\n", cksum16((uint16 *)udphdr2, sizeof(struct tcp), pseudo)); printf("%x\n", cksum16((uint16 *)udphdr2, sizeof(struct tcp), pseudo2)); // uint16 src; // uint16 dst; // uint32 seq; // uint32 ack; // uint8 off; // uint8 flg; // uint16 win; // uint16 sum; // uint16 urg; // printf("seq ntohs %u\n", ntohs(seq)); // printf("seq ntohs %u\n", ntohl( seq)); // printf("ack %u\n", ntohl ( udphdr->ack )); udphdr->ack = htonl(ntohl(seq) + 1); ack = udphdr2->seq; seq = udphdr2->ack; // uint8_t *buf; // memcpy(udphdr2 + 1, buf, sizeof(20)); printf("ack %u\n", ntohl(ack)); printf("seq %u\n", ntohl(seq)); // struct udp *udphdr; // udphdr = mbufpushhdr(m2, *udphdr); // // put the UDP header // udphdr = mbufpushhdr(m, *udphdr); // udphdr->sport = htons(sport); // udphdr->dport = htons(dport); // udphdr->ulen = htons(m->len); // udphdr->sum = 0; // zero means no checksum is provided // // 172.18.86.160 // R(172, 16, 100, 2) tmp = (172 << 24) | (16 << 16) | (100 << 8) | (1 << 0); // now on to the IP layer // struct mbuf *m2; // m2 = mbufalloc(MBUF_DEFAULT_HEADROOM); // if (!m2) // return -1; // if (copyin(pr->pagetable, mbufput(m, n), addr, n) == -1) // { // mbuffree(m); // return -1; // } // udphdr = mbufpullhdr(m, *udphdr); sport = 1; dport = 2; printf("src%d\n", ntohs(udphdr->src)); printf("dst %d\n", ntohs(udphdr->dst)); printf("%d\n", sizeof(udphdr2)); printf("%d\n", sizeof(udphdr)); // char *obuf = "a message from xv6!"; // mbufput(m2, sizeof(obuf)); // m2->len = m2->len+sizeof(obuf); if (count222 == 0) { flg2 = (1 << 4) | (1 << 1); udphdr2->flg = flg2; net_tx_ip(m2, IPPROTO_TCP, tmp); // net_tx_ip(m2, IPPROTO_TCP, tmp); // net_tx_ip(m2, IPPROTO_TCP, tmp); // net_tx_ip(m2, IPPROTO_TCP, tmp); // net_tx_ip(m2, IPPROTO_TCP, tmp); // net_tx_ip(m2, IPPROTO_TCP, tmp); // net_tx_ip(m2, IPPROTO_TCP, tmp); // mbuffree(m2); count222++; mbuffree(m2); } else { // flg2 = (1 << 4); // udphdr2->flg = flg2; // net_tx_ip(m, IPPROTO_TCP, tmp); // udphdr2->flg = flg2; // net_tx_ip(m2, IPPROTO_TCP, tmp); } // } // else sockrecvudp2(m, tmp, dport, sport); // sip = htonl(local_ip);; // sockrecvudp(m, sip, dport, sport); // printf("-------------------\n"); // sockrecvudp2(m, tmp, dport, sport); return; fail: mbuffree(m); } ``` 算是比較作弊的方式，最近比較忙沒空看檢查碼這部分哪裡有問題，最後看到我的程式碼成功收到來自xv6 的確認封包。 ![](https://i.imgur.com/2vpVYJk.jpg) 這些問題解決完後面要做的事情就是 ![](https://i.imgur.com/WTtyChi.png) ![](https://i.imgur.com/mtDdeFO.png) 增加http 協議和 arp 緩存，要看有沒有時間去弄了，最近整理一下再放github
Last changed by  
 
x213212
https://x8795278.blogspot.com/
700
Published on HackMD