1. Supporting Protocols and Technologies in TCP/IP Suites
Asst. Prof. Chaiporn Jaikaeo, Ph.D.
Computer Engineering Department
Kasetsart University, Bangkok, Thailand
Adapted from the notes by Lami Kaya and lecture slides from Anan Phonphoem
© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.
© The McGraw-Hill Companies, Inc.

2. Outline Address Resolution Protocol (ARP)
Internet Control Message Protocol (ICMP)
Dynamic Host Configuration Protocol (DHCP)
Network Address Translation (NAT)

3. Address Resolution Protocol (ARP)

4. Address Resolution Recall the forwarding process
Forwarding uses IP addresses
A MAC address is needed to communicate with the next hop
IP must translate the next-hop IP address to a MAC address
The translation process is known as address resolution
Address resolution is local to a network

5. Address Resolution
One computer can resolve the address of another computer only if both computers attach to the same physical network
Resolve
Resolve
Resolve
Resolve

6. ARP RFC 826 - Address Resolution Protocol
ARP maps any network level address (such as IP) to its corresponding data link address (such as Ethernet)
Supporting protocol in data link layers
Not data link layer protocol itself

7. ARP Protocol Station 1 is looking for MAC add of IP 158.109.33.200 1 24
ARP request
I’m looking for IP
ARP request

8. ARP Protocol Station 3 (IP 158.109.33.200) responses 1 2 3 4
ARP response
I’m IP
My physical address is
A-C2-23
ARP response

9. Conceptual Address Boundary

10. ARP Cache Sending an ARP request for each datagram is inefficient
Three frames traverse the network for each datagram
ARP request, ARP response, and the data datagram itself
ARP cache is used to reduce network traffic
ARP saves the information from a response
so it can be used for subsequent packets
The software does not keep the information indefinitely
Instead, ARP maintains a small table of bindings in memory

11. ARP from Command Prompt
entry in ARP table
C:\> arp -a
( ) at 0:0:e8:15:cc:c
$ ping garnet.cpe.ku.ac.th :
router.cpe.ku.ac.th ( ) at 0:0:c:6:13:4a
cc.cpe.ku.ac.th ( ) at 2:60:8c:2e:b5:8b

12. Error Reporting Mechanisms

13. Error Reporting Mechanisms
IP problems
Best effort
Data can be
lost, duplicate, delay, out-of-order
Error detection of IP
checksum
if error, discard frame (cannot send back error message – no trust in the header)
IP requires additional helpers
Internet Control Message Protocol (ICMP)

14. ICMP RFC 792 IP supporter For error generating
Transmission problem
Time to live (TTL) exceed
Destination unreachable
etc.
Serve as useful diagnostic tools
ping, traceroute

15. ICMP ICMP error messages never generates due to:
ICMP error messages themselves
Broadcast/Multicast (prevent broadcast Storms)
What are Broadcast Storms ?
A large number of broadcast frames transmitted nearly simultaneous
LAN may freeze!

16. ICMP encapsulation frame hdr Frame data IP hdr IP data type code ……...
e.g. Ethernet
IP hdr IP data
contain
protocol 0x01
(ICMP)
type code ……...
indicate error type

17. Ethernet Frame Containing ICMP packetDA T IP
header
Type SA
Code
Other info.
Frame (Ethernet) Header
IP Header
ICMP 8
Echo request
Echo reply
Type
Code
Description 11
Time exceed 3
Port unreachable

18. ICMP header type - relevant ICMP message
code - more detail information
checksum - covers ICMP header/data (not IP header)
type: code: checksum:16
Content specific

19. ICMP Messages

20. Diagnostic Tools: ping
ping request
ping reply
Generate an ICMP echo request
Receive the ICMP echo reply
All TCP/IP node is supposed to implement ICMP and respond to ICMP echo

21. ping command (#1) Send a single echo request / wait for a reply
Resend another request if no reply (1 sec.)
Repeat until receive at least one reply or stop after time out
> ping iwing.cpe.ku.ac.th
iwing.cpe.ku.ac.th is alive
> ping happy.cpe.ku.ac.th
no answer from happy.cpe.ku.ac.th

22. ping command (#2) Send an echo request message every seconds
Records the time it takes for each reply
Every echo request contains a unique sequence number to match replies and request
Record round-trip timing
Perform packet lost statistics

23. ping example $ ping iwing.cpe.ku.ac.th
PING iwing.cpe.ku.ac.th ( ) from : 56(84) bytes of data.
Warning: time of day goes back, taking countermeasures.
64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=0 ttl=252 time=1.187 msec
64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=1 ttl=252 time=601 usec
64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=2 ttl=252 time=594 usec
64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=3 ttl=252 time=594 usec
64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=4 ttl=252 time=585 usec
64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=5 ttl=252 time=590 usec
64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=6 ttl=252 time=584 usec
64 bytes from iwing.cpe.ku.ac.th ( ): icmp_seq=7 ttl=252 time=587 usec
--- iwing.cpe.ku.ac.th ping statistics ---
8 packets transmitted, 8 packets received, 0% packet loss
round-trip min/avg/max/mdev = 0.584/0.665/1.187/0.198 ms

24. ping as debugging tools
What we get from ping?
Timing information
Connection reliability
Destination is reachable (routable)
IP layer is functional, but no guarantee for other higher layer protocols

25. ping results No response Lost packet (significant when >2-3%)
Target host inactive or no connection
Lost packet (significant when >2-3%)
Transmission error on WAN/LAN
Overloading bridges/routers
Varying round-trip time
host/network overloading
No lost and round-trip time is reasonably constant
Congratulations! That’s all we want.

26. Diagnostic Tools: traceroute
Command to determine the active route to a destination address
How does it work?
send a UDP messages to an unused port on the target host with ttl=1
router decrease ttl to 0, it has to return an ICMP time exceed message
traceroute sets ttl =2 and retransmits, this time go one more hop
ttl++ until UDP messages reach the destination.
the target returns an ICMP service unavailable because there is no UDP port service.

27. How traceroute works?
UDP(TTL =1)
Destination unused port #

28. How traceroute works? UDP(TTL =1) ICMP(time exceed) TTL = 0

29. How traceroute works? TTL = 0 ICMP(time exceed) UDP(TTL =1)

30. How traceroute works? UDP(TTL =8) UDP(TTL =9) ICMP(port unreachable)

31. Traceroute example $ traceroute iwing.cpe.ku.ac.th
traceroute to iwing.cpe.ku.ac.th ( ), 30 hops max, 38 byte packets
1 fe-cpegw2-server ( ) ms ms ms
2 gb-cpegwbb-cpegw ( ) ms ms ms
3 gb-cpec4k6-cpec6k ( ) ms ms ms
4 iwing ( ) ms ms ms

32. Traceroute example $ traceroute www.umass.edu
traceroute to ( ), 30 hops max, 38 byte packets
1 fe-cpegw2-server ( ) ms ms ms
2 gb-cpegwbb-cpegw ( ) ms ms ms
( ) ms ms ms
( ) ms ms ms
( ) ms ms ms
( ) ms ms ms
( ) ms ms ms
( ) ms ms ms
9 S1-1.R00.LA-POP.uni.net.th ( ) ms ms ms
( ) ms ms ms
11 snvang-losang.abilene.ucaid.edu ( ) ms ms ms
12 dnvrng-snvang.abilene.ucaid.edu ( ) ms ms *
13 kscyng-dnvrng.abilene.ucaid.edu ( ) ms ms ms …
19 nox300gw1-PEER-NoX-UMASS nox.org ( ) ms ms ms
20 lgrc-rt gw.umass.edu ( ) ms ms ms
21 lgrc-rt gw.umass.edu ( ) ms ms ms
22 * * *
23 * * *

33. Dynamic Host Configuration Protocol (DHCP)

34. DHCP
Allows a computer to join a new network and obtain networking parameters automatically
IP address
Subnet mask
Default router (gateway) address
DNS server's address
etc.
The concept has been termed plug-and-play networking

35. DHCP Message Format

36. DHCP DISCOVER (Broadcast)
DHCP Operation
DHCP Server
Client
Boot
DHCP DISCOVER (Broadcast)
DHCP OFFER
DHCP REQUEST
DHCP ACK 36

37. DHCP Discover Message
Broadcast by clients

38. DHCP Offer Message
Sent directly to client

39. Assigned Address Types
We can configure a DHCP server to supply two types of addresses:
Permanently assigned addresses
Typically assigned to servers
A pool of dynamic addresses to be allocated on demand
Typically assigned to arbitrary hosts

40. Address Leasing DHCP issues a lease on the address for a finite period
Thus allows a DHCP server to reclaim addresses
When a lease expires, a host can choose to relinquish the address or renegotiate with DHCP to extend the lease
If approved, a computer continues to operate without any interruption
If a server denies an extension request, the host must stop using the address 40

41. DHCP Relay Agents DHCP discover messages are broadcast locally
These messages are not forwarded by routers
Router
DHCP Server
New client
DHCP DISCOVER
Assuming all networks are /24

42. Example: DHCP Relay Agents
Each network may be equipped with a DHCP relay
Typically built into a router
Router & DHCP Relay
DHCP Server
New client 2
DHCP DISCOVER (Unicast) 1
DHCP DISCOVER
Assuming all networks are /24

43. Example: DHCP Relay Agents
Each network may be equipped with a DHCP relay
Typically built into a router
Router & DHCP Relay
DHCP Server
New client 3
DHCP OFFER 5 4
DHCP OFFER
Client accepts IP
Assuming all networks are /24

44. Example: DHCP Relay Agents
Each network may be equipped with a DHCP relay
Typically built into a router
Router & DHCP Relay
DHCP Server
New client 8
DHCP ACK 7
DHCP REQUEST 6
DHCP REQUEST
DHCP ACK 9
Assuming all networks are /24

45. Network Address Translation (NAT)

46. Network Address Translation
NAT – Network Address Translation
A function that translates the address of datagrams into a new address
Typically, original address is private (unroutable)
New address is public and routable

47. Private Addresses
Internet routers will not route packets whose destination addresses fall within these ranges 47

48. Address Translation Table:
Basic NAT Operation
Address Translation Table:
Inside
Outside
NAT Router
SA =
DA =
SA =
DA =
SA =
DA =
SA =
DA =

49. Address Translation Table:
Address Pooling
SA =
DA =
NAT Router
SA =
DA =
SA =
DA =
SA =
DA =
Address Translation Table:
Inside
Outside :

50. Advantages of Using NAT
Eliminates need to reassign addresses when changing to a new ISP
Protects network security
Balances load
Preserves IP addresses
SA =
DA =
SA =
DA =
SA =
DA =
SA =
DA =

51. Port Translation
Single public IP address is mapped to multiple hosts in a private network
In this case, NAT router modifies the port numbers for outgoing traffic
Known as NAPT or PAT

52. Address Translation Table:
NAPT Operation
Address Translation Table:
Inside
Outside
:2322
:4511
NAT Router
SA = :2322
DA = :80
SA = :4511
DA = :80
SA = :80
DA = :2322
SA = :80
DA = :4511

53. NAT/NAPT for Home Users
Wireless router has NAT/NAPT functionality built in
Along with DHCP and switch functionalities
Map all IP addresses to single routable address
Wireless Router
Internet
DSL/Cable Modem