NAME

        rfc2765_4.1_hoplimit.seq - Verify IPv6 <-> IPv4 header 
        translation in accordance with RFC2765 [SIIT]

TARGET

        Router

SYNOPSIS

         rfc2765_4.1_hoplimit.seq [-tooloption ...] 
        -p rfc2765_3.1_hoplimit.def

INITIALIZATION

	Before this test starts, run initialize.seq.

TEST PROCEDURE

        This test verifies that NUT properly translates Hop Limit - 1 to 
        TTL, or sends an ICMPv6 Time Exceeded.
        
        Network Topology

        Link0
        --------------------------
            |               |
           TN              NUT
            |               |
        --------------------------
        Link1

        TN -- (Link0) -- NUT        NUT -- (Link1) -- TN
        
        ---------------------      ------------------------

        1.1.
        ===================>
        ICMPv6 Echo Request
                IPv6 Header
                        src address : TN LINK0 IPv4 embedded IPv6 address
                        dst address : TN LINK1 IPv4 embedded IPv6 address
                        Hop Limit = 255
                ICMPv6 echo request
         
        1.2.
        <<JUDGMENT>>
                                   ===================>
        ICMPv4 Echo request
                IPv4 Header
                        src address : TN LINK0 IPv4 address
                        dst address : TN LINK1 IPv4 address
                        Don't Fragment = 1
                        TTL = 254
                ICMPv4 echo request

        2.1.
        ===================>
        ICMPv6 Echo Request
                IPv6 Header
                        src address : TN LINK0 IPv4 embedded IPv6 address
                        dst address : TN LINK1 IPv4 embedded IPv6 address
                        Hop Limit = 64
                ICMPv6 echo request
         
        2.2.
        <<JUDGMENT>>
                                   ===================>
        ICMPv4 Echo request
                IPv4 Header
                        src address : TN LINK0 IPv4 address
                        dst address : TN LINK1 IPv4 address
                        Don't Fragment = 1
                        TTL = 63
                ICMPv4 echo request

        3.1.
        ===================>
        ICMPv6 Echo Request
                IPv6 Header
                        src address : TN LINK0 IPv4 embedded IPv6 address
                        dst address : TN LINK1 IPv4 embedded IPv6 address
                        Hop Limit = 2
                ICMPv6 echo request
         
        3.2.
        <<JUDGMENT>>
                                   ===================>
        ICMPv4 Echo request
                IPv4 Header
                        src address : TN LINK0 IPv4 address
                        dst address : TN LINK1 IPv4 address
                        Don't Fragment = 1
                        TTL = 1
                ICMPv4 echo request

        4.1.
        ===================>
        ICMPv6 Echo Request
                IPv6 Header
                        src address : TN LINK0 IPv4 embedded IPv6 address
                        dst address : TN LINK1 IPv4 embedded IPv6 address
                        Hop Limit = 1
                ICMPv6 echo request
         
        4.2.
        <<JUDGMENT>>
        <===================
        ICMPv6 Time Exceeded
                IPv6 Header
                        src address : TN LINK0 IPv4 embedded IPv6 address
                        dst address : TN LINK1 IPv4 embedded IPv6 address
                ICMPv6 Time Exceeded
                        Type = 3
                        Code = 0 (hop limit exceeded in transit)
                        data = ICMPv6 Echo Request

JUDGMENT

        << PASS >>
                NUT translates ICMPv6 with Hop Limit = 255, 64, 2 to 
                ICMPv4 with TTL = 254, 63, 1.
                NUT responds to ICMPv6 Echo Request with TTL = 1
                with an ICMPv6 Time Exceeded message.
                
        << FAIL >>      
                NUT doesn't translate Hop Limit properly, or doesn't 
                respond with ICMPv6 Time Exceeded messages when 
                Hop Limit = 1 on incoming packages.

NOTE

REFERENCE

RFC2765

4.1. Translating IPv6 Headers into IPv4 Headers

   If there is no IPv6 Fragment header the IPv4 header fields are set as
   follows:

         Time to Live:
                 Hop Limit value copied from IPv6 header.  Since the
                 translator is a router, as part of forwarding the
                 packet it needs to decrement either the IPv6 Hop
                 Limit (before the translation) or the IPv4 TTL (after
                 the translation).  As part of decrementing the TTL or
                 Hop Limit the translator (as any router) needs to
                 check for zero and send the ICMPv4 or ICMPv6 "ttl
                 exceeded" error.