NAME

        Pkt_Too_Big - Verify that the NUT sends Packet Too Big Message

TARGET

        Router

NETWORK CONFIGURATION

        This test is OFFLINK Network Configuration test.
        In this test, TN play a Roll of the Router.
        
        Physical Network configuration
        
        Link0   
        --------+---------------+--------------
                |               |
                NUT             TN
                |               |
        --------+---------------+--------------
        Link1

        Logical Network Configuration

                        Host A (TN-Link0)
                        |                                       Link0
        --------+-------+-----------------
                | 
                NUT (globaladdress:B)
                |
        --------+-------+-----------------
                        |                                       Link1
                        Router(TN-Link1)
                        |
        ----------------+-------+---------
                                |
                                HOST B (OFFLINK_LINK1_GLOBAL_ADDRESS)

        In this configuration, Packets are send and received.

        for example,
                In Logical
                        HOST B           -- Echo Reply --> NUT
                Actually, in physical
                        TN (as Router)   -- Echo Reply --> NUT

INITIALIZATION

        TN attempt to execute remote command 'vRemote(route.rmt)'.
        'route add -inet6 OFFLINK_LINK1_GLOBAL_ADDRESS TN-LINK1-address'

        And status of Neighbor Cache Entry for TN's addresses are reachable.

TEST PROCEDURE

        This test verifies that the node sends a Packet Too Big Message 
        in response to a packet that it can not forward because the packet 
        is larger than the MTU of the outgoing link.

        TN                      NUT

        ---------------------------

        1.
        After NUT is initialized (set static route) , NUT sets 
        the Link MTU of LINK1 Interface to 1300 .

        2.
        TN send Echo Request to Host B.

         === echo request  ===>

        3.
        NUT send Packet Too Big Message

         <=== Packet Too Big Message ===

JUDGMENT

        
        << PASS >>
                NUT send a Packet Too Big Message.

        << FAIL >>      
                NUT do not send a Packet Too Big Message.

REFERENCE

RFC2463 3.2 Packet Too Big Message

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |     Code      |          Checksum             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             MTU                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +               as will fit without the ICMPv6 packet           +
      |               exceeding the minimum IPv6 MTU [IPv6]           |

   IPv6 Fields:

   Destination Address

                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           2

   Code           Set to 0 (zero) by the sender and ignored by the
                  receiver

   MTU            The Maximum Transmission Unit of the next-hop link.

  Description

   A Packet Too Big MUST be sent by a router in response to a packet
   that it cannot forward because the packet is larger than the MTU of
   the outgoing link.  The information in this message is used as part
   of the Path MTU Discovery process [PMTU].

   Sending a Packet Too Big Message makes an exception to one of the
   rules of when to send an ICMPv6 error message, in that unlike other
   messages, it is sent in response to a packet received with an IPv6
   multicast destination address, or a link-layer multicast or link-
   layer broadcast address.