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ITEC4610 Network Switching and Routing ดร. ประวิทย์ ชุมชู หัวหน้าสาขาวิชาวิศวกรรมสารสนเทศและการสื่ อสาร(ICE) MUT Email: [email protected] ห้องทางาน: F402 เบอร์โทรศัพท์ที่ทางาน: (02)9883655 ต่อ 220 เบอร์โทรศัพท์เคลื่อนที่: 065343850 MUT Class IV ICMPv4, IPv6 และ ICMPv6 ดร. ประวิทย์ ชุมชู หัวหน้าสาขาวิชาวิศวกรรมสารสนเทศและการสื่ อสาร(ICE) MUT Email: [email protected] ห้องทางาน: F402 เบอร์โทรศัพท์ที่ทางาน: (02)9883655 ต่อ 220 เบอร์โทรศัพท์เคลื่อนที่: 065343850 MUT หัวข้อที่บรรยาย Introduction • ICMPv4 • IPv6 • ICMPv6 MUT Introduction ระดับชั้นสื่ อสารที่ 3 ของ TCP/IP IGMP ICMP ICMPv6 IPv4 IPv6 ARP RARP Network layer in IPv4 IGMP = will talk in the class of multicasting ICMPv4= This class IPv4 = Last Class ARP = Last Classes MUT IPv6 = This class ICMPv6 = This class Network layer in IPv6 หัวข้อที่บรรยาย • Introduction ICMPv4 • IPv6 • ICMPv6 MUT Internet Control Message Protocol version 4 Objectives Upon completion you will be able to: • Be familiar with the ICMP message format • Know the types of error reporting messages • Know the types of query messages • Be able to calculate the ICMP checksum • Know how to use the ping and traceroute commands • Understand the modules and interactions of an ICMP package MUT Position of ICMP in the network MUT ICMP encapsulation ICMP is network layer protocol but its messages are first encapsulated inside IP datagrams Protocol Field in IP header =1 MUT TYPES OF MESSAGES ICMP messages are divided into error-reporting messages and query messages. The error-reporting messages report problems that a router or a host (destination) may encounter. The query messages get specific information from a router or another host. MUT ICMP messages MUT MESSAGE FORMAT An ICMP message has an 8-byte header and a variable-size data section. Although the general format of the header is different for each message type, the first 4 bytes are common to all. Type : defined in the previous slide Code: the reason for particular message types Checksum: calculated over the entire message (header and data). Rest of the header: specific for each message types MUT DATA: Error message information for finding the error packet Query messages extra information ERROR REPORTING IP, as an unreliable protocol, is not concerned with error checking and error control. ICMP was designed, in part, to compensate for this shortcoming. ICMP does not correct errors, it simply reports them. The topics discussed in this section include: Destination Unreachable Source Quench Time Exceeded Parameter Problem Redirection MUT Note: ICMP always reports error messages to the original source. MUT Error-reporting messages MUT Note: The following are important points about ICMP error messages: ❏ No ICMP error message will be generated in response to a datagram carrying an ICMP error message. ❏ No ICMP error message will be generated for a fragmented datagram that is not the first fragment. ❏ No ICMP error message will be generated for a datagram having a multicast address. ❏ No ICMP error message will be generated for a datagram having a special address such as 127.0.0.0 or 0.0.0.0. MUT Contents of data field for the error messages 8 bytes : Received datagram IP header: Sent datagram IP header : MUT Destination-unreachable format MUT Error code • • • • • • • • • • • • • • • • MUT 0 : The network is unreachable 1 : The host is unreachable 2 : The protocol is unreachable 3 : The port is unreachable 4 : Fragmentation is required 5 : Source routing could not be accomplished 6 : The destination network is unknown 7 : The destination host is unknown 8 : The source is isolated 9 : Communication with the destination network is administratively prohibited 10 : Communication with the destination host is administratively prohibited 11 : The network is unreachable for the specified type of service 12 : The host is unreachable for the specified type of service 13 : The host is unreachable because the administrator has put a filter on it 14 : The host is unreachable because the host precedence is violated 15 : The host is unreachable because the host precedence was cut off Note: Destination-unreachable messages with codes 2 or 3 can be created only by the destination host. Other destination-unreachable messages can be created only by routers. MUT Note: A router cannot detect all problems that prevent the delivery of a packet. MUT Note: There is no flow-control mechanism in the IP protocol. MUT Source-quench format Cause of Congestion MUT Note: A source-quench message informs the source that a datagram has been discarded due to congestion in a router or the destination host. The source must slow down the sending of datagrams until the congestion is relieved. MUT Note: One source-quench message is sent for each datagram that is discarded due to congestion. MUT Note: Whenever a router decrements a datagram with a time-to-live value to zero, it discards the datagram and sends a time-exceeded message to the original source. MUT Note: When the final destination does not receive all of the fragments in a set time, it discards the received fragments and sends a time-exceeded message to the original source. MUT Note: In a time-exceeded message, code 0 is used only by routers to show that the value of the time-to-live field is zero. Code 1 is used only by the destination host to show that not all of the fragments have arrived within a set time. MUT Time-exceeded message format - TTL MUT - Timeout Note: A parameter-problem message can be created by a router or the destination host. MUT Parameter-problem message format 0: Wrong header MUT 1: Need options Redirection concept MUT Note: A host usually starts with a small routing table that is gradually augmented and updated. One of the tools to accomplish this is the redirection message. MUT Redirection message format MUT Note: A redirection message is sent from a router to a host on the same local network. MUT QUERY ICMP can also diagnose some network problems through the query messages, a group of four different pairs of messages. In this type of ICMP message, a node sends a message that is answered in a specific format by the destination node. The topics discussed in this section include: Echo Request and Reply Timestamp Request and Reply Address-Mask Request and Reply Router Solicitation and Advertisement MUT Query messages MUT Note: An echo-request message can be sent by a host or router. An echo-reply message is sent by the host or router which receives an echo-request message. MUT Note: Echo-request and echo-reply messages can be used by network managers to check the operation of the IP protocol. MUT Note: Echo-request and echo-reply messages can test the reachability of a host. This is usually done by invoking the ping command. MUT Echo-request and echo-reply messages MUT Echo-request and echo-reply messages MUT Note: Timestamp-request and timestampreply messages can be used to calculate the round-trip time between a source and a destination machine even if their clocks are not synchronized. MUT Note: The timestamp-request and timestampreply messages can be used to synchronize two clocks in two machines if the exact one-way time duration is known. MUT Mask-request and mask-reply message format MUT Router-solicitation message format MUT Router-advertisement message format MUT CHECKSUM In ICMP the checksum is calculated over the entire message (header and data). The topics discussed in this section include: Checksum Calculation Checksum Testing MUT Example 1 The following Figure shows an example of checksum calculation for a simple echo-request message. We randomly chose the identifier to be 1 and the sequence number to be 9. The message is divided into 16-bit (2-byte) words. The words are added together and the sum is complemented. Now the sender can put this value in the checksum field. See Next Slide MUT Example of checksum calculation MUT DEBUGGING TOOLS We introduce two tools that use ICMP for debugging: ping and traceroute. The topics discussed in this section include: Ping Traceroute MUT Example 2 We use the ping program to test the server fhda.edu. The resul is shown below: $ ping fhda.edu PING fhda.edu (153.18.8.1) 56 (84) bytes of data. 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=0 ttl=62 time=1.91 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=1 ttl=62 time=2.04 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=2 ttl=62 time=1.90 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=3 ttl=62 time=1.97 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=4 ttl=62 time=1.93 ms See Next Slide MUT Example 2 (Continued) 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=5 ttl=62 time=2.00 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=6 ttl=62 time=1.94 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=7 ttl=62 time=1.94 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=8 ttl=62 time=1.97 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=9 ttl=62 time=1.89 ms 64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=10 ttl=62 time=1.98 ms --- fhda.edu ping statistics --11 packets transmitted, 11 received, 0% packet loss, time 10103ms rtt min/avg/max = 1.899/1.955/2.041 ms MUT Example 3 For the this example, we want to know if the adelphia.net mail server is alive and running. The result is shown below: $ ping mail.adelphia.net PING mail.adelphia.net (68.168.78.100) 56(84) bytes of data. 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=0 ttl=48 time=85.4 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=1 ttl=48 time=84.6 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=2 ttl=48 time=84.9 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=3 ttl=48 time=84.3 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=4 ttl=48 time=84.5 ms See Next Slide MUT Example 3 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=5 ttl=48 time=84.7 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=6 ttl=48 time=84.6 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=7 ttl=48 time=84.7 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=8 ttl=48 time=84.4 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=9 ttl=48 time=84.2 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=10 ttl=48 time=84.9 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=11 ttl=48 time=84.6 ms 64 bytes from mail.adelphia.net (68.168.78.100): icmp_seq=12 ttl=48 time=84.5 ms --- mail.adelphia.net ping statistics --14 packets transmitted, 13 received, 7% packet loss, time 13129ms rtt min/avg/max/mdev = 84.207/84.694/85.469 MUT Example 3 MUT Example 4 We use the traceroute program to find the route from the computer voyager.deanza.edu to the server fhda.edu. The following shows the result: $ traceroute fhda.edu traceroute to fhda.edu (153.18.8.1), 30 hops max, 38 byte packets 1 Dcore.fhda.edu (153.18.31.254) 0.995 ms 0.899 ms 0.878 ms 2 Dbackup.fhda.edu (153.18.251.4) 1.039 ms 1.064 ms 1.083 ms 3 tiptoe.fhda.edu (153.18.8.1) 1.797 ms 1.642 ms 1.757 ms See Next Slide MUT Example 4 (Continued) The un-numbered line after the command shows that the destination is 153.18.8.1. The TTL value is 30 hops. The packet contains 38 bytes: 20 bytes of IP header, 8 bytes of UDP header, and 10 bytes of application data. The application data is used by traceroute to keep track of the packets. The first line shows the first router visited. The router is named Dcore.fhda.edu with IP address 153.18.31.254. The first round trip time was 0.995 milliseconds, the second was 0.899 milliseconds, and the third was 0.878 milliseconds. The second line shows the second router visited. The router is named Dbackup.fhda.edu with IP address 153.18.251.4. The three round trip times are also shown. The third line shows the destination host. We know that this is the destination host because there are no more lines. The destination host is the server fhda.edu, but it is named tiptoe. fhda.edu with the IP address 153.18.8.1. The three round trip times are also shown. MUT Example 5 In this example, we trace a longer route, the route to xerox.com $ traceroute xerox.com traceroute to xerox.com (13.1.64.93), 30 hops max, 38 byte packets 1 Dcore.fhda.edu (153.18.31.254) 0.622 ms 0.891 ms 0.875 ms 2 Ddmz.fhda.edu (153.18.251.40) 2.132 ms 2.266 ms 2.094 ms ... 18 alpha.Xerox.COM (13.1.64.93) 11.172 ms 11.048 ms 10.922 ms Here there are 17 hops between source and destination. Note that some round trip times look unusual. It could be that a router is too busy to process the packet immediately. MUT Example 6 An interesting point is that a host can send a traceroute packet to itself. This can be done by specifying the host as the destination. The packet goes to the loopback address as we expect. $ traceroute voyager.deanza.edu traceroute to voyager.deanza.edu (127.0.0.1), 30 hops max, 38 byte packets 1 voyager (127.0.0.1) 0.178 ms 0.086 ms 0.055 ms MUT Example 7 Finally, we use the traceroute program to find the route between fhda.edu and mhhe.com (McGraw-Hill server). We notice that we cannot find the whole route. When traceroute does not receive a response within 5 seconds, it prints an asterisk to signify a problem, and then tries the next hop.. $ traceroute mhhe.com MUT traceroute to mhhe.com (198.45.24.104), 30 hops max, 38 byte packets 1 Dcore.fhda.edu (153.18.31.254) 1.025 ms 0.892 ms 0.880 ms 2 Ddmz.fhda.edu (153.18.251.40) 2.141 ms 2.159 ms 2.103 ms 3 Cinic.fhda.edu (153.18.253.126) 2.159 ms 2.050 ms 1.992 ms ... 16 * * * 17 * * * ............... ICMP PACKAGE To give an idea of how ICMP can handle the sending and receiving of ICMP messages, we present our version of an ICMP package made of two modules: an input module and an output module. The topics discussed in this section include: Input Module Output Module MUT ICMP package MUT คาถาม? MUT แบบฝึ กหัดท้ายบทลองทาดู L5 L4 L3 L2 L1 H 1 8 DATA 1010101011….. 1 L3 L3 C L2 L2 L2 B L2 L1 L1 L1 L1 A L1 101011….. 101011….. L3 L1 IPA1=X,IPA2=Z IPA1=W,IPA2=Y IPA1=2, IPA2=3 IPA1=4, IPA2=5 SA DA DATA ถ้ าแพ็คเก็ตหายทีจ่ ุดต่ าง ๆ ดังรู ป ICMP ตอบสนองอย่ างไรบ้ าง A, B, C, D, E, F,G 3 C IPA=8 IPA1=6, IPA2=7 SA=Source IP Address DA=Destination IP Address IPA=IP Address H MUT L2 L1 101010….. 2 A IPA=1 B L2 L1 L5 L4 G L3 F L2 D E L1 1010101010001011….. D เฉลย • • • • • • • MUT A = ไม่ทาอะไรเลย B = ไม่ทาอะไรเลย C = แจ้ง error D = ไม่ทาอะไรเลย E = ไม่ทาอะไรเลย F = ไม่ทาอะไรเลย G = แจ้ง error แบบฝึ กหัดท้ายบทลองทาดู • Exercise 13: How can we determine if an IP packet is carrying an ICMP packet? MUT เฉลย • Protocol field in IP header = 1 MUT แบบฝึ กหัดท้ายบทลองทาดู • Exercise 17: An ICMP message has arrived with the header (in hexadecimal): 03 03 10 20 00 00 00 00 00 – What is the type of the message? – What is the code ? – What is purpose of the message ? MUT เฉลย 8 bits Type 8 bits 16 bits Code Checksum Rest of the header Data section 8 bits 03 8 bits 03 00 00 00 00 Data section – What is the type of the message? • Type = 03 = destination is unreachable – What is the code ? • Code = 03 = the port is not available – What is purpose of the message ? MUT • Informs the sender that the port is not available 16 bits 1020 แบบฝึ กหัดท้ายบทลองทาดู • ถ้าคุณต้องการทราบว่าคอมพิวเตอร์ IPv4 เครื่ องหนึ่งมีการเปิ ดให้บริ การ โปรแกรมประยุกต์อะไรบ้างนักศึกษาสามารถทาได้อย่าง ถ้านักศึกษามี คอมพิวเตอร์ที่มีการเชื่อมต่อเครื อข่าย IPv4 กับคอมพิวเตอร์เครื่ องนั้น MUT เฉลย (port scanning) • สร้างแพ็คเก็ต UDP แล้วส่ งไปยังเครื่ องคอมพิวเตอร์น้ นั โดยการเปลี่ยน หมายเลขพอร์ตปลายทางแล้วดู ICMP packets ถ้าไม่ได้เปิ ดพอร์ตนั้นจะ ตอบกลับด้วย ICMP แพ็คเก็ตดังรู ปต่อไปนี้ MUT Code = 3 หัวข้อที่บรรยาย • Introduction • ICMPv4 IPv6 • ICMPv6 MUT Next Generation: IPv6 and ICMPv6 Objectives Upon completion you will be able to: • Understand the shortcomings of IPv4 • Know the IPv6 address format, address types, and abbreviations • Be familiar with the IPv6 header format • Know the extension header types • Know the differences between ICMPv4 and ICMPv6 • Know the strategies for transitioning from IPv4 to IPv6 MUT IPv6 IPv6 has these advantages over IPv4: 1. larger address space 128 bits 32 bits 2. better header format keep header overhead to a minimum 3. new options additional functionalities 4. allowance for extension for new technologies or applications 5. support for resource allocation using flow label for QoS 6. support for more security confidentially and integrity of the packets The topics discussed in this section include: IPv6 Addresses Address Space Assignment Packet Format Comparison between IPv4 and IPv6 MUT IPv6 address MUT Abbreviated address MUT Abbreviated address with consecutive zeros ย่ อได้ ครั้งเดียวเท่ านั้นต่ อ 1 หมายเลข IP MUT CIDR address MUT Address structure See next slide for types of prefix MUT Type prefixes for IPv6 addresses MUT Provider-based address Type identifier 010:a provider-based address Registry 11000:North America 01000:European MUT 10100:Asian and Pacific countries Address hierarchy Provider prefix an ISP, variable-length Subscriber prefix an organization subscriber, 24 bits Subnet prefix a network under a territory of the subscriber, 32 bits Node Identifier the identity of node connected to the subnet 48 bits MUT Unspecified address For: - a host does no know its own address - A host sends an inquiry to find its address MUT Loopback Address For: -used by a host to test itself without going on the networks MUT Compatible address -Used when a computer using IPv6 wants to send a packet to another computer using IPv6 - the packet passes through IPv4 networks IPv6 IPv4 IPv6 0x02 2 0x0D13 MUT 0x1117 0x0E14 Mapped address For: -Used when a computer that has migrated to IPv6 want to sent a packet to a computer still using IPv4 MUT Link local address For: - Used in an isolated network - Does not have a global effect MUT Site local address For: -Used for a site with several networks - Used in isolated networks - Does not have a global effect MUT Multicast address For: - For a group of hosts MUT IPv6 datagram MUT Format of an IPv6 datagram Version: version 6 Priority: packet priorities Flow label: a particular flow of data Payload length: length of IP datagram excluding the base header(40 bytes) Next Header: Header following the base header Hop limit: TTL MUT Source Address: the original source IP address Destination Address: the final destination IP address Next header codes MUT Priorities for congestion-controlled traffic MUT Priorities for noncongestion-controlled traffic MUT Comparison between IPv4 and IPv6 packet header MUT Extension header format MUT Extension header types MUT Hop-by-hop option header format Used when the source needs to pass information to all router visited by the datagram MUT The format of options in a hop-by-hop option header MUT Pad1 MUT PadN MUT Jumbo payload For: - normally the IP datagram can be a maximum of 65535 bytes - Jumbo payload =2^32-1 (4,294,967,295 bytes) MUT Source routing MUT Source routing example MUT Fragmentation - Only the source could do - PATH MTU Discovery technique -If no path MTU discovery, a size of 576 bytes of smaller MUT Authentication MUT Calculation of authentication data The authentication header validates the message sender and ensures the integrity of data MUT Encrypted security payload Providing confidentiality (รักษาความลับ) and guards against eavesdropping (ดังฟัง) MUT Transport mode encryption MUT Tunnel-mode encryption MUT Comparison between IPv4 options and IPv6 extension headers MUT คาถาม? MUT แบบฝึ กหัดลองทาดู • Exercise 2: Show the original (unabbreviated) form of the following address: a. b. c. d. MUT 0::0 0:AA::0 0:1234::3 123::1:2 เฉลย a. 0::0 a. b. 0:AA::0 a. c. 0000:1234:0000:0000:0000:0000:0000:0000:0003 123::1:2 a. MUT 0000:00AA:0000:0000:0000:0000:0000:0000:0000 0:1234::3 a. d. 0000:0000:0000:0000:0000:0000:0000:0000:0000 0123:0000:0000:0000:0000:0000:0000:0001:0002 แบบฝึ กหัดลองทาดู • Exercise 3: What is the type of the following addresses: a. b. c. d. MUT FE80::12 FEC0::24A2 FE02::0 0::01 เฉลย First 10 bits = 1111111010 Link local address First 10 bits = 1111111011Site local address First byte = 11111111 Multicast address a. b. c. d. FE80::12 11111110:1000000:12 a. FEC0::24A2 11111110:1010000:24A2 a. Link local address FF02::0 11111110:0000 a. Multicast 0::01 a. MUT Link local address Loopback Address แบบฝึ กหัดลองทาดู • MUT Exercise 14: A host has the address 581E:1456:2314:ABCD::1211. If the node identification is 48 bits and the subnet identification is 32 bits, find the provider prefix? เฉลย The provider prefix is the type identifier plus registry identifier plus provider identifier (3 + 5 + 16 = 24 bits). • • • • MUT 581E:1456:2314:ABCD:0000:0000:0000:1211010110000011110:1456:2314:ABCD::1211 Node identifier = 48 bits Subnet identifier = 32 bits The prefix provider =581E:14 แบบฝึ กหัด • Exercise 28: what is the ip-compatible address for 119.254.254.254? MUT เฉลย • 119.254.254.254->77.FE.FE.FE IP-compatible = 0::77FE:FEFE MUT แบบฝึ กหัด • Exercise 29: what is the ip-mapped address for 119.254.254.254? MUT เฉลย • 119.254.254.254->77.FE.FE.FE IP-mapped address = 0::FFFF:77FE:FEFE MUT หัวข้อที่บรรยาย • Introduction • ICMPv4 • IPv6 ICMPv6 MUT ICMPv6 ICMPv6, while similar in strategy to ICMPv4, has changes that makes it more suitable for IPv6. ICMPv6 has absorbed some protocols that were independent in version 4. The topics discussed in this section include: Error Reporting Query MUT Comparison of network layers in version 4 and version 6 MUT Categories of ICMPv6 messages MUT General format of ICMP messages MUT Error-reporting messages Destination Unreachable: The same concept as in ICMPv4 Packet too big: a router receives a packet that is larger than MTU Time exceed: Have not arrived within the time limit Parameter problems: Error in header fields, an unrecognized extension header, an unrecognized option Redirection: the same concept as in ICMPv4 MUT Comparison of error-reporting messages in ICMPv4 and ICMPv6 MUT Destination-unreachable message format 0: No path to destination 1: Communication is prohibited 2: Strict source routing is impossible. 3: Destination address is unreachable. 4: Port is not available. MUT Packet-too-big message format MUT Time-exceeded message format 0: a hop limit field =0 1: not arrived within the time limit for fragments of datagram MUT Parameter-problem message format 0: Error in header fields 1:an unrecognized extension header 2: an unrecognized option MUT Redirection message format MUT Query messages MUT Comparison of query messages in ICMPv4 and ICMPv6 MUT Echo request and reply messages MUT Router-solicitation and advertisement message formats MUT Neighbor-solicitation and advertisement message formats MUT Group-membership messages MUT Group-membership message formats MUT Four situations of group-membership operation MUT TRANSITION FROM IPv4 TO IPv6 Three strategies have been devised by the IETF to provide for a smooth transition from IPv4 to IPv6. The topics discussed in this section include: Dual Stack Tunneling Header Translation MUT Three transition strategies MUT Dual stack MUT Automatic tunneling MUT Configured tunneling MUT Header translation MUT Header translation MUT Summary • • • • MUT ICMPv4 IPv6 ICMP6 Next Class RIPv1 และ RIPv2 คาถาม? MUT แบบฝึ กหัดลองทาดู • Exercise 18: what type of ICMP messages contain of the IP datagram? Why is this included? MUT เฉลย • • • • • • MUT destination unreachable: type 1 packet too big: type 2 time exceeded: type 3 parameter problem: type 4 Redirection: type 137 The IP header and first 8 bytes of data are included because this data contains all of the information needed for the source of the datagram to identify the packet in question, including the destination address and the source and destination port addresses.