1. The University of Adelaide, School of Computer Science
13 September 2018
Chapter 4
Advanced Internetworking
Copyright © 2010, Elsevier Inc. All rights Reserved
Chapter 2 — Instructions: Language of the Computer

2. The University of Adelaide, School of Computer Science
13 September 2018
Problems
How do we build a routing system that can handle hundreds of thousands of networks and billions of end nodes?
How to handle address space exhaustion of IPV4?
How to enhance the functionalities of Internet?
Chapter 2 — Instructions: Language of the Computer

3. The University of Adelaide, School of Computer Science
13 September 2018
Chapter Outline
Global Internet
Multicast
Mobile IP
Chapter 2 — Instructions: Language of the Computer

4. The University of Adelaide, School of Computer Science
13 September 2018
Chapter Goal
Understanding the scalability of routing in the Internet
Discussing IPv6
Understanding the concept of multicasting
Discussing Mobile IP
Chapter 2 — Instructions: Language of the Computer

5. The University of Adelaide, School of Computer Science
13 September 2018
The Global Internet
The tree structure of the Internet in 1990
Chapter 2 — Instructions: Language of the Computer

6. The University of Adelaide, School of Computer Science
13 September 2018
The Global Internet
A simple multi-provider Internet
Chapter 2 — Instructions: Language of the Computer

7. The University of Adelaide, School of Computer Science
13 September 2018
The Global Internet
Chapter 2 — Instructions: Language of the Computer

8. Interdomain Routing (BGP)
Internet is organized as autonomous systems (AS) each of which is under the control of a single administrative entity
Autonomous System (AS)
corresponds to an administrative domain
examples: University, company, backbone network
A corporation’s internal network might be a single AS, or the network of a single Internet service provider

9. A network with two autonomous system
Interdomain Routing
A network with two autonomous system

10. Route Propagation
Idea: Provide an additional way to hierarchically aggregate routing information in a large internet.
Improves scalability
Divide the routing problem in two parts:
Routing within a single autonomous system
Routing between autonomous systems
Another name for autonomous systems in the Internet is routing domains
Two-level route propagation hierarchy
Inter-domain routing protocol (Internet-wide standard)
Intra-domain routing protocol (each AS selects its own)

11. EGP and BGP Inter-domain Routing Protocols
Exterior Gateway Protocol (EGP)
Forced a tree-like topology onto the Internet
Did not allow for the topology to become general
Tree like structure: there is a single backbone and autonomous systems are connected only as parents and children and not as peers
Border Gateway Protocol (BGP)
Assumes that the Internet is an arbitrarily interconnected set of ASs.
Today’s Internet consists of an interconnection of multiple backbone networks (they are usually called service provider networks, and they are operated by private companies rather than the government)
Sites are connected to each other in arbitrary ways

12. BGP
Some large corporations connect directly to one or more of the backbone, while others connect to smaller, non-backbone service providers.
Many service providers exist mainly to provide service to “consumers” (individuals with PCs in their homes), and these providers must connect to the backbone providers
Often many providers arrange to interconnect with each other at a single “peering point”

13. BGP-4: Border Gateway Protocol
Assumes the Internet is an arbitrarily interconnected set of AS's.
Define local traffic as traffic that originates at or terminates on nodes within an AS, and transit traffic as traffic that passes through an AS.
We can classify AS's into three types:
Stub AS: an AS that has only a single connection to one other AS; such an AS will only carry local traffic.
Multihomed AS: an AS that has connections to more than one other AS, but refuses to carry transit traffic.
Transit AS: an AS that has connections to more than one other AS, and is designed to carry both transit and local traffic.

14. BGP-4: Border Gateway Protocol

15. BGP
The goal of Inter-domain routing is to find any path to the intended destination that is loop free
We are concerned with reachability than optimality
Finding path anywhere close to optimal is considered to be a great achievement

16. BGP
Scalability: An Internet backbone router must be able to forward any packet destined anywhere in the Internet
Having a routing table that will provide a match for any valid IP address
Autonomous nature of the domains
It is impossible to calculate meaningful path costs for a path that crosses multiple ASs
A cost of 1000 across one provider might imply a great path but it might mean an unacceptable bad one from another provider
Issues of trust
Provider A might be unwilling to believe certain advertisements from provider B

17. BGP Each AS has: One BGP speaker that advertises:
local networks
other reachable networks (transit AS only)
gives path information
In addition to the BGP speakers, the AS has one or more border “gateways” which need not be the same as the speakers
The border gateways are the routers through which packets enter and leave the AS

18. BGP
BGP does not belong to either of the two main classes of routing protocols (distance vectors and link-state protocols)
BGP advertises complete paths as an enumerated lists of ASs to reach a particular network

19. Example of a network running BGP
BGP Example
Example of a network running BGP

20. BGP Example Speaker for AS 2 advertises reachability to P and Q
Network , , , and , can be reached directly from AS 2.

21. BGP Example Speaker for backbone network (AS1) then advertises
Networks , , , and can be reached along the path <AS 1, AS 2>.
Speaker can also cancel previously advertised paths

22. BGP Issues
It should be apparent that the AS numbers carried in BGP need to be unique
For example, AS 2 can only recognize itself in the AS path in the example if no other AS identifies itself in the same way
AS numbers are 16-bit numbers assigned by a central authority

23. Integrating Interdomain and Intradomain Routing
All routers run an intradomain routing protocol (RIP/ OSPF). Border routers (A, D, E) also run BGP to other ASs

24. Integrating Interdomain and Intradomain Routing
128/69/16
18.0/16
12.5.5/24
128.34/16
BGP routing table, IGP routing table, and combined table at router B

25. Routing Areas A domain divided into area Backbone area
Area border router (ABR)
A domain divided into area

26. Next Generation IP (IPv6)

27. IPv6 Background
IP has been patched (subnets, supernets) but there is still the fundamental 32 bit address limitation
IETF started effort to specify new version of IP in 1991
New version would require change of header
Include all modifications in one new protocol
Solicitation of suggestions from community
Result was IPng which became IPv6
First version completed in ’94
Same architectural principles as v4 – only bigger 

28. IPv6 Issues Address length: usable addresses vs. overhead
Hop limit: is 64K necessary?
Max. Pkt. Size: Larger bandwidth calls for larger pkts.
Is the checksum necessary?
How do servers handle both types of packets?
Is security necessary in IP?
How is it best implemented?
DNS can be very important in the transition – how?

29. IPv6 planned support list
128-bit address space
This is what it’s all about…
Real-time/QoS services
Security and authentication
Autoconfiguration
Hosts autoconfig with IP address and domain name
Idea is to try to make systems more plug-n-play
Enhanced routing functionality e.g,. Mobile hosts
Multicast
Protocol extensions
Smooth transition path from IPv4
Can’t do it all at once!

30. Address Space and Notation
Allocation is classless
Prefixes specify different uses (unicast, multicast, anycast)
Anycast: send packets to nearest member of a group
Prefixes can be used to map v4 to v6 space and vice-versa
Lots of flexibility with 128 bits!
~1500 address/sqft of the earths surface

31. Address Space and Notation
Standard representation is set of eight 16-bit values separated by colons
E.g.,
27CD:1234:3200:0000:0000:4325:B792:0428
If there are large number of zeros, they can be omitted with series of colons:
27CD:1234:3200::4325:B792:0428
Address prefixes (slash notation) are the same as v4
FEDC:BA98:7600::/40 describes a 40 bit prefix

32.
Reserved
Unassigned
Reserved for NSAP (non-IP addresses used by ISO)
Reserved for IPX (non-IP addresses used by IPX)
0000 1
0001
001
Unicast Address Space
010
011
100
101
110
1110
1111 0
Link Local Use addresses
Site Local Use addresses
Multicast addresses

33. Unicast Assignment in v6
Unicast address assignment is similar to CIDR
Unicast addresses start with 001
Host interfaces belong to subnets
Addresses are composed of a subnet prefix and a host identifier
Subnet prefix structure provides for aggregation into larger networks

34. Unicast Assignment in v6
Provider-based plan
Idea is that the Internet is global hierarchy of network
Three levels of hierarchy – region, provider, subscriber
Goal is to provide route aggregation to reduce BGP overhead
A provider can advertise a single prefix for all of its subscribers
Region = 13 bits, Provider = 24 bits, Subscriber = 16 bits, Host = 80 bits
E.g., 001,regionID,providerID,subscriberID,subnetID,intefaceID
Anycast addresses are treated just like unicast addresses
It’s up to the routing system to determine which server is “closest”

35. IPv6 Header 40-byte “base” header Extension headers fragmentation
source routing
authentication and
security
other options

36. Packet Format Details Simpler format than v4 Version = 6
Traffic class same as v4 ToS
Treat all packets with the same Flow Label equally
Support QoS and fair bandwidth allocation
Payload length does not include header –limits packets to 64KB
There is a “jumbogram option”

37. Packet Format Details Hop limit = TTL field
Next header combines options and protocol
If there are no options then NextHeader is the protocol field
Options are “extension header” that follow IP header
Ordered list of tuples – 6 common types
Quickly enable a router to tell if the options are meant for it
E.g., routing, fragmentation, authentication encryption…

38. Key differences in header
No checksum
Bit level errors are checked for all over the place
No length variability in header
Fixed format speeds processing
No more fragmentation and reassembly in header
Incorrectly sized packets are dropped and message is sent to sender to reduce packet size
Hosts should do path MTU discovery
But of course we have to be able to segment packets!

39. Transition from v4 to v6
Dual stack operation – v6 nodes run in both v4 and v6 modes and use version field to decide which stack to use
Nodes can be assigned a v4 compatible v6 address
Allows a host which supports v6 to talk v6 even if local routers only speak v4
Signals the need for tunneling
Add 96 0’s (zero-extending) to a 32-bit v4 address –
e.g., ::

40. Transition from v4 to v6 Nodes can be assigned a v4 mapped v6 address
Allows a host which supports both v6 and v4 to communicate with a v4 hosts
Add 2 bytes of 1’s to v4 address then zero-extend the rest – e.g.,
::ffff:
Tunneling is used to deal with networks where v4 router(s) sit between two v6 routers
Simply encapsulate v6 packets and all of their information in v4 packets until you hit the next v6 router

41. IPv4-Mapped IPv6 Address
80 bits of 0s followed by 16 bits of ones, followed by a 32 bit IPv4 Address:
(::ffff: )
FFFF
IPv4 Address
80 bits
16 bits
32 bits

42. IPv4-Mapped IPv6 Address
IPv4-Mapped addresses allow a host that support both IPv4 and IPv6 to communicate with a host that supports only IPv4.
The IPv6 address is based completely on the IPv4 address.

43. Works with DNS
An IPv6 application asks DNS for the address of a host, but the host only has an IPv4 address.
DNS creates the IPv4-Mapped IPv6 address automatically.
Kernel understands this is a special address and really uses IPv4 communication.

44. IPv4-Compatible IPv6 Address
An IPv4 compatible address allows a host supporting IPv6 to talk IPv6 even if the local router(s) don’t talk IPv6.
IPv4 compatible addresses tell endpoint software to create a tunnel by encapsulating the IPv6 packet in an IPv4 packet.

45. Tunneling (done automatically by kernel when IPv4-Compatible IPv6 addresses used)
Host
IPv6
Host
IPv4 Routers
IPv4 Datagram
IPv6 Datagram

46. Internet Multicast

47. Overview IPv4 Integral part of IPv6 class D addresses
demonstrated with Multicast Backbone (Mbone) virtual network [1992].
uses tunneling
Integral part of IPv6
problem is making it scale

48. Overview One-to-many Many-to-many Radio station broadcast
Transmitting news, stock-price
Software updates to multiple hosts
Many-to-many
Multimedia teleconferencing
Online multi-player games
Distributed simulations

49. Overview Without multicast support:
A source needs to send a separate packet with the identical data to each member of the group
This redundancy consumes more bandwidth
Redundant traffic is not evenly distributed, concentrated near the sending host
Source needs to keep track of the IP address of each member in the group
Group may be dynamic
To support many-to-many and one-to-many IP provides an IP-level multicast

50. Overview
Basic IP multicast model is many-to-many based on multicast groups
Each group has its own IP multicast address
Hosts that are members of a group receive copies of any packets sent to that group’s multicast address
A host can be in multiple groups
A host can join and leave groups

51. Overview
Using IP multicast to send the identical packet to each member of the group
A host sends a single copy of the packet addressed to the group’s multicast address
The sending host does not need to know the individual unicast IP address of each member
Sending host does not send multiple copies of the packet

52. Overview
IP’s original many-to-many multicast has been supplemented with support for a form of one-to-many multicast
One-to-many multicast
Source specific multicast (SSM)
A receiving host specifies both a multicast group and a specific sending host
Many-to-many model
Any source multicast (ASM)

53. Overview
A host signals its desire to join or leave a multicast group by communicating with its local router using a special protocol
In IPv4, the protocol is Internet Group Management Protocol (IGMP)
In IPv6, the protocol is Multicast Listener Discovery (MLD)
The router has the responsibility for making multicast behave correctly with regard to the host

54. Multicast Routing
To support multicast, a router must additionally have multicast forwarding tables that indicate, based on multicast address, which links to use to forward the multicast packet
Unicast forwarding tables collectively specify a set of paths
Multicast forwarding tables collectively specify a set of trees
Multicast distribution trees

55. Multicast Routing
To support source specific multicast, the multicast forwarding tables must indicate which links to use based on the combination of multicast address and the unicast IP address of the source
Multicast routing is the process by which multicast distribution trees are determined

56. Distance-Vector Multicast
Each router already knows that shortest path for every destination in its table.
When a router receives a multicast packet from S, it forwards the packet on all outgoing links (except the one on which the packet arrived), iff packet arrived from N.
Eliminate duplicate broadcast packets by only letting
“parent” for LAN (relative to S) forward
shortest path to S (learn via distance vector)
smallest address to break ties

57. Distance-Vector Multicast
Reverse Path Broadcast (RPB)
Goal: Prune networks that have no hosts in group G
Step 1: Determine LAN that is a leaf with no members in G
leaf if parent is only router on the LAN
determine if any hosts are members of G using IGMP
Step 2: Propagate “no members of G here” information
augment <Destination, Cost> update sent to neighbors with set of groups for which this network is interested in receiving multicast packets.
only happens when multicast address becomes active.

58. Protocol Independent Multicast (PIM)
Shared Tree
Source specific tree

59. Protocol Independent Multicast (PIM)
Delivery of a packet along a shared tree. R1 tunnels the packet to the RP, which forwards it along the shared tree to R4 and R5.

60. The University of Adelaide, School of Computer Science
13 September 2018
Summary
# Chapter Subtitle
We have looked at the issues of scalability in routing in the Internet
We have discussed IPV6
We have discussed Multicasting
Chapter 2 — Instructions: Language of the Computer