1. Chapter 15. Internet Protocol
Principles of Internetworking
Connectionless Internetworking
Internet Protocol, ICMP
IPv6 (IPNG)
Multicasting

2. Internetworking Terms
A collection of communications networks interconnected by bridges and/or routers
Subnetwork
Refers to a constituent network of an internet
End system (ES)
A device attached to one of the subnetworks of an internet that is used to support end-user applications or services

3. Internetworking Terms (cont)
Intermediate System (IS)
A device used to connect two subnetworks and permit communication between end systems attached to different subnetworks
Bridge
An IS used to connect two LANs that use identical LAN protocols
Operates an layer 2 of the OSI model
Router
An IS used to connect two networks that may or may not be similar
Operates at layer 3 of the OSI model

4. Internetworking Protocols

5. Internetworking Mode Connection-mode operation
Each IS splices together two virtual circuits
Virtual circuit
is set up across
each subnet
Subnet 2 IS M IS I
Subnet 4
Subnet 1 IS K
DTE A
DTE B IS J
Subnet 3 IS L

6. Internetworking Mode (cont)
Connectionless-mode operation
For each incoming PDU, the IS makes a separate routing decision
DTE A makes a
separate routing
decision for each PDU, choosing either IS I or J
Subnet 2 IS M IS I
Subnet 4
Subnet 1 IS K
DTE A
DTE B IS J
Subnet 3 IS L

7. Internet Protocol Operation

8. Internet Protocol Operation (cont)

9. IP Design Issues Routing Datagram lifetime
static/dynamic routing table
Datagram lifetime
Using hop count
Fragmentation and Reassembly
In IP, datagram fragments are reassembled at the destination end system
Fields used by the IP segmentation techniques
Data Unit Identifier (ID): source and destination address, an identifier of the protocol layer, a sequence number supplied by that protocol layer
Data Length, Offset, More-flag

10. IP Design Issues (cont)

11. Internet Protocol IP Services Send ( Source address
Destination address
Protocol
Type of service indicators
Identifier
Don’t-fragment identifier
Time to live
Data length
Option data
Data )
Deliver (
Source address
Destination address
Protocol
Type of service indicators
Data length
Option data
Data )
IP user

12. Internet Protocol (cont)
IP service quality options
Precedence: 8 levels
Reliability: 2 levels (normal or high)
Delay: 2 levels (normal or high)
Throughput: 2 levels (normal or high)
Currently defined options
Security
Allows a security label to be attached to a datagram

13. Internet Protocol (cont)
Source routing
A sequenced list of router addresses that specifies the route to be followed
Route Recording
A field is allocated to record the sequence of routers visited by the datagram
Stream identification
Names reserved resources used for stream services
Timestamping
The source IP entity and some or all intermediate routes add a timestamp to the data unit as it goes by

14. Internet Protocol (cont)

15. IP Header Fields Internet header length (IHL) (4 bits)
Length of header in 32-bit words
Minimum value is five, for a min. header length of 20 octets
Type of service (8 bits)
Specifies precedence, reliability, delay and throughput parameters
Total length (16 bits)
Total datagram length, in octets

16. IP Header Fields (cont)
Identification (16 bits)
A sequence number that, together with the source address, destination address, and user protocol, is intended to identify a datagram uniquely
Flags (3 bits)
Only two bits are currently defined
More bit: for fragmentation and reassembly
Don’t Fragment bit: prohibits fragmentation

17. IP Header Fields (cont)
Fragment offset (13 bits)
Indicates where in the original datagram this fragment belongs, measured in 64-bit unit
Time to live (8 bits)
Specifies how long, in seconds, a datagram is allowed to remain in the internet
Every router that processes a datagram must decrease the TTL by at least one, so the TTL is somewhat similar to a hop count

18. IP Header Fields (cont)
Protocol (8 bits)
Indicates the next higher protocol that is to receive the data field at the destination
Header checksum (16 bits)
This is re-verified and recomputed at each router
Option (variable)
Padding (variable)
Used to ensure that the datagram header is a multiple of 32 bits in length

19. IP Addresses
1 ~
128 ~
192 ~
224 ~

20. Subnets, Subnet Masks
host portion of the internet address is partitioned into a subnet number and a host number

21. Subnets, Subnet Masks (cont)
Address mask: allows the host to determine whether an outgoing datagram is destined for a host on the same LAN (send directly) or another LAN (send datagram to router)

22. Example of Subnetworking
Class C x
Subnet mask
Routing table?

23. ICMP Internet Control Message Protocol ICMP messages
Provides feedback about problems in the communication environment
ICMP messages
Destination unreachable
Time exceeded
Parameter problem
Source quench
Redirect
Echo, Echo reply
Timestamp, Timestamp reply
Address mask request/reply

24. ICMP Messages Destination unreachable
A router may return this message if it does not know how to reach the destination network
A particular host is unreachable
The destination host itself may return this message if the user protocol or some higher-level service access point is unreachable
The datagram specifies a source route that is unusable
If a router must fragment a datagram but the Don’t-Fragment flag is set

25. ICMP Messages (cont) Time exceeded Parameter problem Source quench
A router will return this message if the lifetime of the datagram expires
A host will send this message if it cannot complete reassembly within a time limit
Parameter problem
A syntactic or semantic error in an IP header
Source quench
This message can be used by a router or host that must discard datagrams because of a full buffer

26. ICMP Messages (cont) Redirect Echo and Echo reply
A router sends this message to a host on a directly connected router to advise the host of a better route to a particular destination
Echo and Echo reply
Provide a mechanism for testing that communication is possible between entities
Timestamp and Timestamp reply
Provide a mechanism for sampling the delay characteristics of the internet
Address mask request/reply
Useful for subnets

27. ICMP Messages Format

28. ICMP Messages Format (cont)

29. IPv6 IP Next Generation (IPng) Motivation IPv6 enhancements
The limitation imposed by the 32-bit address field in IPv4
IPv6 enhancements
Expanded address space: 128-bit address
Improved option mechanism
Address autoconfiguration
Increased Addressing Flexibility
Support for resource allocation
Security capabilities

30. IPv6 Packet

31. IPv6 Header

32. IPv6 Header (cont) Traffic class (8 bits) Flow label (20 bits)
Available for use by originating nodes and/or forwarding routers to identify and distinguish between different classes or priorities of IPv6 packets
Still under study
Flow label (20 bits)
May be used by a host to label those packets for which it is requesting special handling by routers

33. IPv6 Header (cont) Payload length (16 bits) Next header (8 bits)
Length of the remainder of the IPv6 packet following the header, in octets.
That is, total length of all of the extension headers plus the transport-level PDU
Next header (8 bits)
Hop limit (8 bits)

34. Flow Label
A flow is uniquely identified by the combination of a source address, destination address, and a nonzero 20-bit flow label
Thus, all packets that are to be part of the same flow are assigned the same flow label by the source
In principle, all of a user’s requirements for a particular flow could be defined in an extension header and included with each packet
Alternatively, IPv6 could make use of the flow requirements for the flow with a unique flow label. In this case, the router must save flow requirement about each flow

35. IPv6 Address Formats

36. IPv6 Extension Headers Hop-by-Hop Options Header Routing Header
Defines special options that require hop-by-hop processing
Routing Header
Similar to IPv4 source routing
Fragment Header
Authentication Header
Encapsulating Security Payload Header
Destination Options Header
Contains optional information to be examined by the destination node

37. IPv6 Extension Headers (cont)

38. Hop-by-Hop options Options definition Jumbo Payload option
Option type (8 bits), Length (8 bits), Option Data (variable)
Jumbo Payload option
Option data field is 32 bits long and gives the length of the packets in octets, excluding the IPv6 header
Payload length field in IPv6 header must be set to zero, and no fragment header
Packet sizes up to more than 4G octets.

39. Hop-by-Hop options (cont)
Router Alert option
Informs the router that the contents of the packet is of interest to the router
The purpose of this option is to provide efficient support for protocols such as RSVP that generate packets that need to be examined by intermediate routers for purpose of traffic control

40. Fragment Header
In IPv6, fragmentation may only be performed by source nodes, not by routers along the path
A node must perform a path discovery algorithm that enables it to learn the smallest MTU supported by any network on the path
Otherwise, limit all packets to 1280 octets

41. ICMPv6 4 error messages 3 informational messages
Destination unreachable
Packet too big
Time exceeded
Parameter problem
3 informational messages
Echo request
Echo reply
Group membership

42. ICMPv6 Message Formats

43. Multicasting
broadcast

44. Multicasting (cont)
Broadcast a copy of each pkt to each network in the configuration

45. IGMP Internet Group Management Protocol Defined in RFC 1112
Used by the hosts and routers to exchange multicast group membership information over a LAN

46. IGMP (cont) Message Format Version: Protocol version = 1 Type Checksum
Type 1: query sent by a multicast router
Type 0: report sent by a host
Checksum
Group Address
Zero in a request message
Valid group address in a report message

47. IGMP (cont) Group Membership with IPv6
ICMPv6 includes all of the functionality of ICMPv4 and IGMP
Multicast support by ICMPv6
Group-membership query message
Group-membership report message
Group-membership termination message