利用p4实现ipv6转发实验

写在前面

只是作为一个入门p4的实验尝试，借用了一些即成的运行代码。

---

p4代码

/**p4_16,v1_model**/

 #include<core.p4>
 #include<v1model.p4>

 const bit<> TYPE_IPV6 = 0x08DD;//ipv6在以太网中的id

 /*HEADERS*/

 typedef bit<> egressSpec_t;
 typedef bit<> macAddr_t;

 header ethernet_t{
     macAddr_t dstAddr;
     macAddr_t srcAddr;
     bit<> etherType;
 }

 header ipv6_t{
     bit<> version;
     bit<> trafficClass;
     bit<> flowLabel;
     bit<> payLoadLen;
     bit<> nextHdr;
     bit<> hopLimit;
     bit<> srcAddr;
     bit<> dstAddr;
 }

 struct metadata{
 }

 struct headers{
     ethernet_t ethernet;
     ipv6_t ipv6;
 }

 /*PARSER*/

 parser MyParser(packet_in packet,out headers hdr,inout metadata meta,inout standard_metadata_t standard_metadata){
     state start{
         transition parse_ethernet;//start开始先以底层eth解析
     }

     state parse_ethernet{
         packet.extract(hdr.ethernet);
         transition select(hdr.ethernet.etherType){
             TYPE_IPV6:parse_ipv6;//转至ipv6解析
             default:accept;
         }
     }

     state parse_ipv6{
         packet.extract(hdr.ipv6);
         transition accept;
     }
 }

 /*CHECKSUM VERIFICATION*/

 control MyVerifyChecksum(inout headers hdr,inout metadata meta){
     apply{}
 }

 /*INGRESS PROCESSING*/

 control MyIngress(inout headers hdr,inout metadata meta,inout standard_metadata_t standard_metadata){
     action drop(){
         mark_to_drop();//将要丢弃的包标记为丢弃
     }

     action ipv6_forward(macAddr_t dstAddr,egressSpec_t port){
         standard_metadata.egress_spec = port;
         hdr.ethernet.srcAddr = hdr.ethernet.dstAddr;
         hdr.ethernet.dstAddr = dstAddr;
         hdr.ipv6.hopLimit = hdr.ipv6.hopLimit - ;//这个类似ipv4中ttl，为0时就超时
     }

     table ipv6_lpm{
         key = {
             hdr.ipv6.dstAddr: lpm;//lpm是最长前缀匹配，exact完全匹配，ternary三元匹配
         }

         actions = {
             ipv6_forward;//转发
             drop;//丢弃
             NoAction;//空动作
         }

         size = ;//流表项容量

         default_action = drop();//table miss则丢弃
     }

     apply{
         if(hdr.ipv6.isValid()){
             ipv6_lpm.apply();
         }
     }
 }

 /*EGRESS PROCESSING*/

 control MyEgress(inout headers hdr,inout metadata meta,inout standard_metadata_t standard_metadata){
     apply{}
 }

 /*CHECKSUM COMPUTATION*/

 control MyComputeChecksum(inout headers hdr,inout metadata meta){
     apply{}
 }

 /*DEPARSER*/

 control MyDeparser(packet_out packet,in headers hdr){
     apply{
         packet.emit(hdr.ethernet);
         packet.emit(hdr.ipv6);
     }
 }

 /*SWITCH*/

 V1Switch(
 MyParser(),
 MyVerifyChecksum(),
 MyIngress(),
 MyEgress(),
 MyComputeChecksum(),
 MyDeparser()
 )main;

---

实验拓扑

这里实验的拓扑用来最简单的一个交换机下挂两个主机，交换机是bmv2。其json文件书写如下： 交换机s1的流表项通过s1-commands.txt文件定义。

 {
     "program": "ipv6_forward.p4",
     "language": "p4-16",
     "targets": {
       "multiswitch": {
           "auto-control-plane": true,
           "cli": true,
           "pcap_dump": true,
           "bmv2_log": true,
           "links": [["h1", "s1"], ["h2", "s1"]],
           "hosts": {
             "h1": {
             },
             "h2": {
             }
           },
           "switches": {
               "s1": {
                   "entries": "s1-commands.txt"
               }
         }
     }
     }
 }

在s1-commans.txt文件中做如下定义：

 table_set_default ipv6_lpm drop
 table_add ipv6_lpm ipv6_forward fe80::5678/128 => 00:04:00:00:00:02 2
 table_add ipv6_lpm ipv6_forward fe80::1234/128 => 00:04:00:00:00:01 1

将其流表项画出来如下：

---

收发包脚本代码

鉴于对python socket发包代码不是那么了解，所以套用了一部分模板做了修改。

send.py

 import argparse
 import sys
 import socket
 import random
 import struct

 from scapy.all import sendp, send, get_if_list, get_if_hwaddr
 from scapy.all import Packet
 from scapy.all import Ether, IPv6, UDP

 def get_if():
     ifs=get_if_list()
     iface=None
     for i in get_if_list():
         if "eth0" in i:
             iface=i
             break;
     if not iface:
         print "Cannot find eth0 interface"
         exit(1)
     return iface

 def main():

     if len(sys.argv)<3:
         print 'pass 3 arguments:<source> <destination> "<message>"'
         exit(1)
     saddr = sys.argv[1]
     addr = sys.argv[2]
     iface = get_if()

     print "sending on interface %s to %s" % (iface, str(addr))
     pkt =  Ether(src=get_if_hwaddr(iface), dst='ff:ff:ff:ff:ff:ff') / IPv6(src=saddr,dst=addr) / UDP(dport=4321, sport=1234) / sys.argv[3]
     pkt.show2()
     sendp(pkt, iface=iface, verbose=False)

 if __name__ == '__main__':
     main()

receive.py

 import sys
 import struct
 import os

 from scapy.all import sniff, sendp, hexdump, get_if_list, get_if_hwaddr
 from scapy.all import Packet, IPOption
 from scapy.all import ShortField, IntField, LongField, BitField, FieldListField, FieldLenField
 from scapy.all import IPv6, TCP, UDP, Raw
 from scapy.layers.inet import _IPOption_HDR

 def get_if():
     ifs=get_if_list()
     iface=None
     for i in get_if_list():
         if "eth0" in i:
             iface=i
             break;
     if not iface:
         print "Cannot find eth0 interface"
         exit(1)
     return iface

 class IPOption_MRI(IPOption):
     name = "MRI"
     option = 31
     fields_desc = [ _IPOption_HDR,
                     FieldLenField("length", None, fmt="B",
                                   length_of="swids",
                                   adjust=lambda pkt,l:l+4),
                     ShortField("count", 0),
                     FieldListField("swids",
                                    [],
                                    IntField("", 0),
                                    length_from=lambda pkt:pkt.count*4) ]
 def handle_pkt(pkt):
     print "got a packet"
     pkt.show2()
     #hexdump(pkt)
     sys.stdout.flush()

 def main():
     ifaces = filter(lambda i: 'eth' in i, os.listdir('/sys/class/net/'))
     iface = ifaces[0]
     print "sniffing on %s" % iface
     sys.stdout.flush()
     sniff(filter="udp and port 4321",iface = iface,
           prn = lambda x: handle_pkt(x))

 if __name__ == '__main__':
     main()

---

测试

 ./run.sh
 //在mininet cli中
 xterm h1 h2
 //在h2中
 ./receive.py
 //在h1中
 ./send.py fe80::1234 fe80::5678 "Hello p4!"

结果如下：

---

牢骚

第一次尝试构建p4相关的实验，了解了一部分p4的语法，以及一些的工作原理，也发掘出一部分并未了解的知识内容待后续去琢磨学习。过程有很多不完美，结果也有很多不完美，虽然现在也不满足，但是寒假也快结束了。