1. Week 9
IPv6
Routing in IP networks

2. Agenda
• IPv6
• Addressing architecture
• Packets
• ICMPv6
• Routing in IP networks

3. IPv6 unicast addresses
interface ID
128 bits
N bits M bits 128-N-M bits
Usually 64 bits
Based on MAC Address
global routing prefix subnet ID
Can be used to identify the
ISP responsible for this address
A subnet in this ISP or
a customer of this ISP

4. IPv6 link-local
• Used by daevdiceds rone ssamsee LAsN to exchange
IPv6 packets when they don't have/need
globally routable address
• Each host/router must generate one link
local address for each of its interfaces
• Each IPv6 host uses several IPv6
addresses
interface ID
128 bits
10 bits 54 bits 64 bits
FE80 0000000000.....00000000000

5. IPv6 Multicast
• An IPv6 multicast address identifies
a group a receivers
Group ID
128 bits
8 bits 4 bits 4 bits 112 bits
11111111 flags scope
Node local-scope
Link-local scope
Subnet local-scope
Site local-scope
Organisation local-scope
Global scope
Permanent Address
Temporary Address
• All hosts : FF02::1
• All routers : FF02::2

6. Agenda
• IPv6
• Addressing architecture
• Packets
• ICMPv6
• Routing in IP networks

7. IPv6 packet format
32 bits
Ver Tclass Flow Label
NxtHdr Hop Limit
Payload Length
Source IPv6 address
(128 bits)
Destination IPv6 address
(128 bits)
Version=6
Traffic class
Size of packet
content in bytes
Unclear utilisation
Same as TTL
Used to identify the type
of the next header found
in the packet payload

8. Sample IPv6
packets
Payload Length
Payload Length
Sequence number
Acknowledgment number
THL Reserved Flags
Window
• Identification of a transport (UDP/TCP) flow
• IPv6 source/destination, Source/Destination
ports
32 bits
Ver Tclass Flow Label
NxtHdr Hop Limit
Source IPv6 address
(128 bits)
Destination IPv6 address
(128 bits)
Source port Destination port
Length Checksum
UDP
32 bits
Ver Tclass Flow Label
NxtHdr Hop Limit
Source IPv6 address
(128 bits)
Destination IPv6 address
(128 bits)
Source port Destination port
Checksum Urgent pointer
TCP
UDP
TCP

9. Packet forwarding
• IPv6 uses longest match
• Example
Destination Gateway
::/0 fe80::dead:beef
::1 ::1
2a02:2788:2c4:16f::/64 eth0
2001:6a8:3080::/48 fe80::bad:cafe
2001:6a8:2d80::/48 fe80::bad:bad
2001:6a8::/32 fe80::aaaa:bbbb
Packets to 2001:6a8:3080::1234,
2001:1890:123a::1:1e,
2001:6a8:3880:40::2

10. Extension headers
• Hop-by-Hop Options
• Routing (Type 0 and Type 2)
• Fragment
• Destination Options
• Authentication
• Encapsulating Security Payload
• Each header must be encoded as n*64
bits

11. Packet fragmentation
• How to handle this network ?
R1 R2
MTU:1500
MTU:1400
MTU:1300

12. Packet fragmentation
• IPv4 used packet fragmentation on routers
• All hosts must handle 576+ bytes
packets
• experience showed fragmentation is
costly for routers and difficult to
implement in hardware
• PathMTU discovery
• widely implemented in TCP stacks

13. P• aIPvc6 kreequtir efsr thaatg evmerye linnk tina thtei on
internet have an MTU of 1280 octets or
more
• Routers do not perform fragmentation
• Only end hosts perform
fragmentation and reassembly by
using the fragmentation header
• But PathMTU discovery should
avoid fragmentation most of the
time

14. A fragmented packet
First fragment Second (and last) fragment
32 bits
Ver Tclass Flow Label
NxtHdr Hop Limit
Payload Length
Source IPv6 address
(128 bits)
Destination IPv6 address
(128 bits)
Source port Destination port
Length Checksum
UDP (first part)
44:fragment
Nxt Hdr Zero Frag. Offset 0 M
Fragment identification = 1234
UDP
32 bits
Ver Tclass Flow Label
NxtHdr Hop Limit
Payload Length
Source IPv6 address
(128 bits)
Destination IPv6 address
(128 bits)
44:fragment
Nxt Hdr Zero Frag. Offset 0 M
Fragment identification = 1234
True
None
False
(end of UDP segment)

15. Agenda
• IPv6
• Addressing architecture
• Packets
• ICMPv6
• Routing in IP networks

16. ICMPv6
• Types of ICMPv6 messages
• Destination (addr,net,port) unreachable
• Packet too big
• Used for PathMTU discovery
• Time expired (Hop limit exhausted)
• Echo request and echo reply
• Multicast group membership
• Router advertisments, Neighbor discovery
• Autoconfiguration

17. ICMPv6 packet
• Type
• ICMPv6 error messages
• 1 Destination Unreachable
• 3 Time Exceeded
• 2 Packet Too Big
• 4 Parameter Problem
• ICMPv6 informational messages:
• 128 Echo Request
• 129 Echo Reply
Ver Tclass Flow Label
NxtHdr Hop Limit
Payload Length
Source IPv6 address
(128 bits)
Destination IPv6 address
(128 bits)
Type Code Checksum
Message body
58 for ICMPv6
Covers ICMPv6 message and part of IPv6 header

18. traceroute6 in details
• Source sends UDP segments with
increasing hop limit
• Intermediate routers reply with ICMP
Time Exceeded messages

19. traceroute6
traceroute6 to star.c10r.facebook.com
(2a03:2880:2130:cf05:face:b00c::1) from
2001:6a8:3080:2:451c:db2:a92f:3d50, 64 hops max, 12 byte packets
1 2001:6a8:3080:2::1 0.329 ms
2 2001:6a8:3000:8000::1 0.582 ms
3 2001:6a8:0:6009::1 1.505 ms
4 2001:7f8:1::a503:2934:1 8.167 ms
5 2620:0:1cff:dead:beef::34c 8.091 ms
6 2620:0:1cff:dead:beef::2d9 13.922 ms
7 2620:0:1cff:dead:beef::2dc 108.487 ms
8 2620:0:1cff:dead:beef::9a7 106.722 ms
9 2620:0:1cff:dead:beef::12a8 103.758 ms
10 2620:0:1cff:dead:beef::999 105.648 ms

20. traceroute
2001:db8:7/48
A’s routing table
destination interface/NH
::/0 2001:db8:7::B
2001:db8:7/48 2001:db8:4::C
2001:db8:1/48 West
2001:db8:4/48 East
2001:db8:7/48 North
B’s routing table
destination interface/NH
::/0 2001:db8:5::C
2001:db8:2/47 2001:db8:6::E
2001:db8:5/48 South
2001:db8:6/48 East
2001:db8:7/48 West
C’s routing table
destination interface/NH
2001:db8:1/48 2001:db8:5::B
2001:db8:2/47 2001:db8:3::E
2001:db8:2/48 2001:db8:5::B
2001:db8:3/48 East
2001:db8:4/48 West
2001:db8:5/48 North
2001:db8:6/47
2001:db8:5::B
E’s routing table
destination interface/NH
::/0 2001:db8:6::B
2001:db8:2/48 East
2001:db8:3/48 West
2001:db8:6/48 North
RA
RB
RC RE
2001:db8:1/48
2001:db8:6/48
2001:db8:5/48
2001:db8:4/48 2001:db8:3/48
2001:db8:2/48

21. Agenda
• IPv6
• Routing in IP networks
• IPv6 subnets
• Routing organization
• Interdomain routing

22. Datalink layer service
• Each device is identified by a 48 bits
MAC address in the datalink layer
• Ethernet, WiFi
• Unicast transmission
• Multicast transmission

23. IPv6 subnet
• A subnet gathers hosts and routers that
can directly exchange frames without
passing through an intermediate route
2001:db8:1234:5678::1
R
2001:db8:1234:5678::/64
2001:db8:1234:5678::AA
2001:db8:1234:5678::BB
2001:db8:1234:5678::CC

24. Issues
• How to easily assign IPv6 addresses to
hosts ?
• Manual configuration is not viable
• How to map IPv6 addresses onto the
corresponding MAC addresses ?

25. IPv6 over Ethernet
IPv6: 2001:0:0:0:8::A
Eth : A
2001:0:0:0:8::A wants to send a packet to 2001:0:0:0:8::C
1
2
Neighbor solicitation: Addr Eth 2001:0:0:0:8::C ? sent to IPv6 multicast address
3
IPv6: 2001:0:0:0:8::E
Eth : E
Ipv6: 2001:0:0:0:8::C
Eth : C
Ipv6: 2001:0:0:0:8::C
Eth : C
IPv6: 2001:0:0:0:8::E
Eth : E
IPv6: 2001:0:0:0:8::A
Eth : A
IPv6: 2001:0:0:0:8::C
Neighbor advertisement: 2001:0:0:0:8::C is reachable via Ethernet Add : C
Eth : C
IPv6: 2001:0:0:0:8::E
Eth : E
IPv6: 2001:0:0:0:8::A
Eth : A

26. Agenda
• IPv6
• Routing in IP networks
• IPv6 subnets
• Routing organization
• Interdomain routing

27. Internet
organisation
• Internet is an internetwork with a large number
of Autonomous Systems (AS)
• an AS is a set of routers that are managed by
the same administrative entity
• Autonomous Systems are interconnected to
allow the transmission of IP packets from any
source to any destination
• On the Internet, most packets need to
travel through several transit Autonomous
Systems

28. Types of domains
• Transit domain
• A transit domain allows external domains to
use its infrastructure to send packets to
other domains
S1
• Examples
T1 T2
T3
S2 S3
S4
• UUNet, OpenTransit, GEANT, Internet2,
RENATER, EQUANT, BT, Telia, Level3,...

29. Stub domains A stub domain does not allow external domains to
use its infrastructure to send packets to other
domains
T1 T2
T3
S1
S2 S3
S4
A stub is connected to at least one transit domain
Content-rich stub domain : Yahoo, Google, MSN,
TF1, BBC,...
Access-rich stub domain : ISPs providing Internet
access via CATV, ADSL, ...

30. Belnet
Source : http://www.belnet.be

31. GEANT
Source : http://www.belnet.be

32. Level3
Source http://www.uu.net

33. Internet routing
• Interior Gateway Protocol (IGP)
• Routing of IP packets inside each domain
• Only knows topology of its domain
Domain1
Domain4
• Exterior Gateway Protocol (EGP)
• Routing of IP packets between domains
• Each domain is considered as a
blackbox
Domain2
Domain3

34. Intradomain routing
• Static routing
• Only useful in very small domains
• Distance vector routing
• Routing Information Protocol (RIP)
• Link-state routing
• Open Shortest Path First (OSPF)
• Intermediate System- Intermediate-System
(IS-IS)

35. Intradomain routing
• Goal
• Allow routers to transmit IP packets along
the best path towards their destination
• best usually means the shortest path
• Shortest measured in seconds or hops
• sometimes best means the less loaded
path
• Alternate routes in case of failures
• Behaviour
• All routers exchange routing information

36. Agenda
• IPv6
• Routing in IP networks
• IPv6 subnets
• Routing organization
• Interdomain routing

37. Interdomain routing
• Goals
• Allow to transmit IP packets along the
best path towards their destination
through several transit domains while
taking into account their routing policies
of each domain without knowing their
detailed topology
• From an interdomain viewpoint, best path
often means cheapest path
• Each domain is free to specify inside its
routing policy the domains for which it
agrees to provide a transit service and
the method it uses to select the best path
to reach each destination

38. Interdomain links
• Private link
• Usually a leased line between two routers
belonging to the two connected domains
R1 R2
DomainA DomainB

39. Interconnection
exchanges
• How to efficiently connect several
domains together ?
R1
R2
R3
R4
Physical link
Interdomain link

40. Routing policies
• In theory BGP allows each domain to define
its own routing policy...
• In practice there are two common policies
• customer-provider peering
• Customer c buys Internet connectivity
from provider P
• shared-cost peering
• Domains x and y agree to exchange
packets without any payment

41. Customer-provider
Customer Provider
peering
AS1 AS2
$ $ $
AS3 AS4
$
• Principle
$
AS7
• Customer sends to its provider internal routes
and routes learned from its customers
• Provider will advertise those routes to the
entire Internet to allow anyone to reach the
Customer
• Provider sends to its customers all known
routes
• Customer will reach anyone on the Internet

42. Customer-provider
peering : example
AS1 AS2
$ $ $
AS3 AS4
• AS7-AS4 peering link
$
• AS7 advertises its routes to AS4
$
AS
7
• AS4 advertises to AS7 all its routes
• AS4-AS2 peering link
Customer-provider
• AS4 advertises its own routes and those of its customers
(AS7)
• AS2 advertises to AS2 all known routes

43. Shared-cost peering
AS1 AS2
AS3 AS4
$
AS7
Customer-provider
$ $ $
$
Shared-cost
• Principle
• PeerX sends to PeerY its internal routes and
the routes learned from its own customers
• PeerY sends to PeerX its internal routes and
the routes learned from its own customers

44. Routing policies
• A domain specifies its routing policy by
defining two sets of filters for each peer
• Import filter
• Specifies which routes can be accepted by
the router among all the received routes
from a given peer
• Export filter
• Specifies which routes can be advertised by
the router to a given peer

45. Routing policies
AS1 AS2
AS3 AS4
$
AS7
Customer-provider
$ $ $
$
Shared-cost
Import policy for AS4
Import: from AS3 accept AS3
import: from AS7 accept AS7
import: from AS1 accept ANY
import: from AS2 accept ANY
Export policy for AS4
export: to AS3 announce AS4 AS7
export: to AS7 announce ANY
export: to AS1 announce AS4 AS7
export: to AS2 announce AS4 AS7
Import policy for AS7
Import: from AS4 accept ANY
Export policy for AS4
export: to AS4 announce AS7