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。

巴特西