若是想要了解 SDN OpenFlow 以及　P4　請不要吝嗇點擊喜歡或是訂閱我喔！(訂閱又不收費XD)
未來有機會也可以跟大家分享我當網管的辛酸血淚史，可以讓人解決問題時可以參考我的文章。

話不多說，我們就累狗!!

def readTableRules(p4info_helper, sw):
    """
    Reads the table entries from all tables on the switch.

    :param p4info_helper: the P4Info helper
    :param sw: the switch connection
    """
    print '\n----- Reading tables rules for %s -----' % sw.name
    for response in sw.ReadTableEntries():
        for entity in response.entities:
            entry = entity.table_entry
            # TODO For extra credit, you can use the p4info_helper to translate
            #      the IDs in the entry to names
            table_name = p4info_helper.get_tables_name(entry.table_id)
            print '%s: ' % table_name,
            for m in entry.match:
                print p4info_helper.get_match_field_name(table_name, m.field_id),
                print '%r' % (p4info_helper.get_match_field_value(m),),
            action = entry.action.action
            action_name = p4info_helper.get_actions_name(action.action_id)
            print '->', action_name,
            for p in action.params:
                print p4info_helper.get_action_param_name(action_name, p.param_id),
                print '%r' % p.value,
            print

def writeTunnelRules(p4info_helper, ingress_sw, egress_sw, tunnel_id,
                     dst_eth_addr, dst_ip_addr):
    """
    Installs three rules:
    1) An tunnel ingress rule on the ingress switch in the ipv4_lpm table that
       encapsulates traffic into a tunnel with the specified ID
    2) A transit rule on the ingress switch that forwards traffic based on
       the specified ID
    3) An tunnel egress rule on the egress switch that decapsulates traffic
       with the specified ID and sends it to the host

    :param p4info_helper: the P4Info helper
    :param ingress_sw: the ingress switch connection
    :param egress_sw: the egress switch connection
    :param tunnel_id: the specified tunnel ID
    :param dst_eth_addr: the destination IP to match in the ingress rule
    :param dst_ip_addr: the destination Ethernet address to write in the
                        egress rule
    """
    # 1) Tunnel Ingress Rule
    table_entry = p4info_helper.buildTableEntry(
        table_name="MyIngress.ipv4_lpm",
        match_fields={
            "hdr.ipv4.dstAddr": (dst_ip_addr, 32)
        },
        action_name="MyIngress.myTunnel_ingress",
        action_params={
            "dst_id": tunnel_id,
        })
    ingress_sw.WriteTableEntry(table_entry)
    print "Installed ingress tunnel rule on %s" % ingress_sw.name

    # 2) Tunnel Transit Rule
    # The rule will need to be added to the myTunnel_exact table and match on
    # the tunnel ID (hdr.myTunnel.dst_id). Traffic will need to be forwarded
    # using the myTunnel_forward action on the port connected to the next switch.
    #
    # For our simple topology, switch 1 and switch 2 are connected using a
    # link attached to port 2 on both switches. We have defined a variable at
    # the top of the file, SWITCH_TO_SWITCH_PORT, that you can use as the output
    # port for this action.
    #
    # We will only need a transit rule on the ingress switch because we are
    # using a simple topology. In general, you'll need on transit rule for
    # each switch in the path (except the last switch, which has the egress rule),
    # and you will need to select the port dynamically for each switch based on
    # your topology.

    # TODO build the transit rule
    # TODO install the transit rule on the ingress switch
    table_entry = p4info_helper.buildTableEntry(
        table_name="MyIngress.myTunnel_exact",
        match_fields={
            "hdr.myTunnel.dst_id": tunnel_id
        },
        action_name="MyIngress.myTunnel_forward",
        action_params={
            "port": SWITCH_TO_SWITCH_PORT
        })
    ingress_sw.WriteTableEntry(table_entry)
    print "Installed transit tunnel rule on %s" % ingress_sw.name

    # 3) Tunnel Egress Rule
    # For our simple topology, the host will always be located on the
    # SWITCH_TO_HOST_PORT (port 1).
    # In general, you will need to keep track of which port the host is
    # connected to.
    table_entry = p4info_helper.buildTableEntry(
        table_name="MyIngress.myTunnel_exact",
        match_fields={
            "hdr.myTunnel.dst_id": tunnel_id
        },
        action_name="MyIngress.myTunnel_egress",
        action_params={
            "dstAddr": dst_eth_addr,
            "port": SWITCH_TO_HOST_PORT
        })
    egress_sw.WriteTableEntry(table_entry)
    print "Installed egress tunnel rule on %s" % egress_sw.name

在此付上我的 Reference，我將會以簡短白話的方式來講解 P4 這套語言，若是你/妳不嫌棄可以訂閱我的發文
每天就根據我自己了解的程度來做發文的動作，如果自己對於 P4也有興趣可以先來預習，那我們明天見！
Reference :
P4_turtorial
[(http://docs.google.com/presentation/d/1zliBqsS8IOD4nQUboRRmF_19poeLLDLadD5zLzrTkVc/edit#slide=id.g37fca2850e_6_1802)]