FH_Reverse - check Fragment Reassembly (reverse order)
Host and Router
FH_Reverse.seq [-tooloption ...] -pkt Fragment.def
-tooloption : v6eval tool option
1. Ping to Target (create Neighbor Cache Entries, if not exist) 2. Override Neighbor Cache Entries
Tester Target
| |
|-------------------------->|
| Echo Request (2nd) |
| |
| |
|-------------------------->|
| Echo Request (1st) |
| |
| |
|<--------------------------|
| Echo Reply |
| |
| |
v v
1. Send Echo Request (2nd fragment) 2. Send Echo Request (1st fragment) 3. Receive Echo Reply
Echo Request Data (original) is:
IPv6 Header
Version = 6
Traffic Class = 0
FlowLabel = 0
PayloadLength = 1032
NextHeader = 58 (ICMP)
SourceAddress = Tester Link Local Address
DestinationAddress = Target Link Local Address
ICMP Echo Request
Type = 128 (Echo Request)
Code = 0
Checksum = (auto)
Identifier = (auto)
SequenceNumber = 0
PayloadData = data repeat{0x1, 512}
data repeat{0x2, 512}
Echo Request Data (1st fragment) is:
IPv6 Header
Version = 6
Traffic Class = 0
FlowLabel = 0
PayloadLength = 528
NextHeader = 44 (Fragment Header)
SourceAddress = Tester Link Local Address
DestinationAddress = Target Link Local Address
Fragment Header
NextHeader = 58 (ICMP)
FragmentOffset = 0
MFlag = 1
Identification = 32bit (Automatic generation)
Payload
data = 520 octets from the head of ICMP Echo request
Echo Request Data (2nd fragment) is:
IPv6 Header
Version = 6
Traffic Class = 0
FlowLabel = 0
PayloadLength = 520
NextHeader = 44 (Fragment Header)
SourceAddress = Tester Link Local Address
DestinationAddress = Target Link Local Address
Fragment Header
NextHeader = 58 (ICMP)
FragmentOffset = 65
MFlag = 0
Identification = 32bit (Automatic generation)
Payload
data = 512 octets from the back of ICMP Echo request
PASS: Echo Reply Received
IPv6 Header
Version = 6
Traffic Class = 0
FlowLabel = 0
PayloadLength = 1032
NextHeader = 58 (ICMP)
SourceAddress = Target Link Local Address
Destination Address = Tester Link Local Address
ICMP Echo Reply
Type = 129 (Echo Reply)
Code = 0
Checksum = (auto)
Identifier = (same as Echo Request)
SequenceNumber = (same as Echo Request)
PayloadData = (same as Echo Request)
RFC2460
4.5 Fragment Header
:
At the destination, fragment packets are reassembled into their original, unfragmented form, as illustrated:
reassembled original packet:
+------------------+----------------------//------------------------+
| Unfragmentable | 2-bit reserved fFragmentablealized to zero for |
| Part | transmission; ignorePart |
+------------------+----------------------//------------------------+
The following rules govern reassembly:
An original packet is reassembled only from fragment packets that
have the same Source Address, Destination Address, and Fragment
Identification.
The Unfragmentable Part of the reassembled packet consists of all
headers up to, but not including, the Fragment header of the first
fragment packet (that is, the packet whose Fragment Offset is
zero), with the following two changes:
The Next Header field of the last header of the Unfragmentable
Part is obtained from the Next Header field of the first
fragment's Fragment header.
The Payload Length of the reassembled packet is computed from
the length of the Unfragmentable Part and the length and offset
of the last fragment. For example, a formula for computing the
Payload Length of the reassembled original packet is:
PL.orig = PL.first - FL.first - 8 + (8 * FO.last) + FL.last
where
PL.orig = Payload Length field of reassembled packet.
PL.first = Payload Length field of first fragment packet.
FL.first = length of fragment following Fragment header of
first fragment packet.
FO.last = Fragment Offset field of Fragment header of
last fragment packet.
FL.last = length of fragment following Fragment header of
last fragment packet.
The Fragmentable Part of the reassembled packet is constructed
from the fragments following the Fragment headers in each of the
fragment packets. The length of each fragment is computed by
subtracting from the packet's Payload Length the length of the
headers between the IPv6 header and fragment itself; its relative
position in Fragmentable Part is computed from its Fragment Offset
value.
The Fragment header is not present in the final, reassembled
packet.
perldoc V6evalTool