Transition Mechanisms for Ipv6 Hosts and Routers RFC2893

1
Transition Mechanisms for Ipv6 Hosts and Routers
RFC2893

• By Michael Pfeiffer

2
Terminology

• IP v4 only node
• IP v6 only node
• IP v4/IP v6 node
• IP v4 compatible IP v6 Address
• High order 96 bits prefix 000000
• Low order 32 bits are the IP v4 address

3
Techniques Used in the Transition

• IP v6-over-IP v4 tunneling
• Configured tunneling
• Automatic tunneling
• IP v4 multicast tunneling

4
Dual IP Layer Operation

• Modes of Operations for IP v4/v6 nodes
• Both stack enabled
• Disabling one or the other stacks
• Tunneling techniques
• None
• Configured tunneling only
• Both configured and automatic tunneling

5
Address configuration

• IP v4/v6 node an have two addresses
• IP v4 address
• 32 bit address
• Acquired using IP v4 addressing mechanisms
• IP v6 address
• 128 bit address
• Acquired using IP v6 addressing mechanisms

6
Domain Name System

• Ability to map between both IP versions
• Example What happen when IP v6 node requests a
  record that as been defined with a IP v4 address
• The resolver libraries must be capable of
  handling both IP v6/IP v4 records

7
DNS

• Returning records to IP v4/v6 nodes
• Filtered
• Return only IP v6 address
• Return only IP v4 address
• Ordered
• Return both addresses
• May change the order of addresses two influence
  the receiving node.

8
Addressing Addresses in the DNS

• Before a IP v4/v6 record is added all of the
  following should be true
• The address is assigned to the interface on the
  node
• The address is configured on the interface.
• The interface is on a link which is connected to
  the IP v6 infastructure.

9
Common Tunneling Mechanisms

• Will take a while to build up IP v6 infastructure
  so we need a means of sending packets
• Tunneling is a way to use IP v4 infrastructure to
  send IP v6 packets
• This is done by sticking a IP v6 packet into the
  body of a IP v4 packet.

10
Types of tunneling

• Configured Tunneling
• Router to Router
• Host to Router

• Automatic Tunneling
• Host to Host
• Router to Host

11
Tunneling Configuration

• 1st The encapsulating node creates an
  encapsulating IP v4 header and transmits
• 2nd The decapsulating node receives the
  encapsulated packet, reassmebles the packet (if
  needed) , and removes the IP v4 header.
• Note(The primary diffence in tunneling scheme is
  how the determine the header packet end address.)

12
Encapsulation

• -------------
• IP v4
• Header
• ------------ -------------
• IP v6 IP v6
• Header Header
• ------------ ------------
• Transport gt
  Transport
• Layer Layer
• Header Header
• ------------ ------------
• Data Data
• ------------ ------------

13
Handling Fragments

• What happens when a IP v6 packet is too big for
  the payload of IP v4 packet?
• IP packet is fragmented and two or more packets
  are send?
• This can be avoided in when the encapsulating
  node knows about the tunneling.

14
Fragmentation Problems

• Fragmentation in tunneling not sent by the
  sending node
• Resassembling packets at the router.

15
Reducing Fragmentation

• Making packet small enough for additional IP v4
  header
• Using a IP v4 Path Discovery Protocal.
• If you have a large number of tunnels then i
  might not be able to store all of them.
• This will not completely elminate fragmentation
  but will reduce it.

16
Hop Limit

• IP v6-over-IP v4 tunnels are considered as one
  hop.
• This means the IP v6 hop limit is decremented by
  one at the end of each tunnel
• This hide the existance of tunneling.
• IP v6 header only gets used at the beginning and
  end of the tunnel.

17
ICMP Errors

• Errors are sent to the encapsulating node
• ICMP packet too big error is handled according
  to the path dicovery
• Which will change the packet along the path
• Handling of other errors depend of the size of
  the packet in error field sent back.

18
IP v4 Header for tunneling

• Version field 4
• IP header length in 32 bit words 5
• Type of service 0
• Note (work is underway to redefine the service
  byte , so this might be different in the future.)
• Total Length (Payload IP v6 header IP v4
  header)

19
IP v4 Header Cont.

• Identification Generated uniquely as for any IP
  v4 packet transmitted by the system.
• Flags
• Don't Fragment flag
• More Fragmentsd flag
• Fragment offset set if there is a fragmentation
• Time to Live Set in implementation specific
  manner

20
IP v4 Header Cont.

• Protocal 41 (Assigned payload type number for IP
  v6)
• Header checksum calculated checksum for the IP
  v4 header
• Source address IP v4 address of encapsulating
  node
• Destination address IP v4 address at end of
  tunnel.

21
Decapsulation

• Accurs when a node recieves a packet with it's IP
  v4 address and the protocal field is set to 41
• Reassembles packet if it was fragmented
• IP v6 header will be untouched since it had been
  encapsulated
• Hop limit will be decremented by one

22
Decapsulation

• Decapsulating node performs IP v4 reassembly
  before decapsulating the IP v6 packet
• Done to preserve all IP v6 options even if
  fragmented
• Node must not forward on decapsulated packet
  unless explicitly configured too.

23
Discarding packets

• The IP v4 header should be discarded
• Node should silently discard packet with an
  invalid IP v4 source address (eg. Multicast,
  broadcast)
• The node should also silently discard packets
  with invalid IP v6 source address

24
Link-Layer Addresses

• Both configured and automatic tunneling must have
  link-local addresses so routing protocal can
  operate
• The Interface Identifier should be the 32 bit
  address that is in the IP v4 header.
• The IP v6 Link-Local address for IP v4 virtual
  interface is FE80IP v4 address

25
Neighor Discovery

• Automatic and unidirectional tunnels are
  condsider undictional
• Neighor discovery is only used for formation of
  link local addresses
• Bidirectional tunnels use Neighbor Unreachability
  Detection (NUD) Packets to setup a tunnel.

26
Configured Tunneling

• Determination of which tunnel to use is done by
  routing table
• Uses prefix mask and match technique
• The Default Route

27
Configured Tunneling with IP v4 Anycast Address

• Uses the Anycast Address to forward the IP v6
  packet on
• Receiving node treats the address as if it is
  it's own
• After decapsulated transmits it toward the
  correct address
• Could have problem with fragmentation

28
Automatic Tunneling

• Allows IP v6/v4 nodes to communicate without
  pre-configured tunnels
• Nodes using automatic tunneling are assigned IP
  v4 compatible addresses.
• IP v4 address is globally unique as long as
  address is not for a private network.

29
Address Configuration

• Will serve as both IP v4 and v6 addresses
• Will acquire address through IP v4 address
  configuration protocols and then Map it to IP v6
  address
• DHCP, BOOTP, RARP, Manual, etc.

30
Automatic Tunneling Operations

• Only used when endpoint address is an IP v4
  compatible address
• A special static routing table can be setup for
  automatic tunneling
• Must not be sent to IP v4 broadcast or multicast
  destinations

31
Source Address cofiguration

• Which format
• Native IP v6
• IP v4 compatible
• Determines the type of traffic that will be
  returned.

32
Work sited

• RFC 2893, http//www.faqs.org/rfc/rfc2893.html