ICMP ICMPv 6 2008 3 7 DPNM Lab

ICMP & ICMPv 6 2008. 3. 7 DPNM Lab. Byungchul Park (fates@postech. ac. kr)

ICMP Internet Control Message Protocol

Introduction ICMP: Internet Control Message Protocol ICMP is often considered part of the IP layer Why the ICMP is needed? Application Telnet, FTP, e-mail, etc Transport Lacks of IP !!! TCP, UDP Network IP, ICMP, IGMP Unreliable and connectionless datagram delivery Link device driver and interface card Best-effort delivery service Lack of error control and lack of assistance mechanisms No error-reporting and error-correcting mechanisms Lacks of mechanism for host and management queries ICMP has been designed to compensate for the above deficiencies.

Introduction ICMP: Internet Control Message Protocol ICMP message are transmitted within IP datagrams Although ICMP is used primarily by IP, it is possible for an application to also access it. (e. g. Traceroute, Ping)

ICMP Messages Types of Messages ICMP message are transmitted within IP datagrams ICMP Messages Error-reporting Query Error reporting : report problems that a router or host may encounter when it processes an IP packet Query message : get specific information from router or a host in order to help a host or network management.

ICMP Messages (cont. ) Types of Messages Category Error-reporting message Type Message 3 Destination unreachable 4 Source quench 11 Time exceeded 12 Parameter problem 5 Redirection 8 or 0 Echo request or reply 13 or 14 Timestamp request and reply 17 or 18 Address mask request and reply 10 or 9 Router solicitation and advertisement Query message

Message Format ICMP Message Format Type : message type(8 bit) Code : specify the reason for the particular message Checksum : 16 bit

Message Format ICMP common field and message Type code description 0 0 3 0 -15 4 0 5 0 -3 8 0 Echo request 9 0 Router advertisement 10 0 Router solicitation 11 0 -1 Time exceeded 12 0 -1 Parameter problem 13 0 Timestamp request 14 0 Timestamp reply 17 0 Address mask request 18 0 Address mask reply Echo reply Destination unreachable Source quench Redirection

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.

Error Reporting ICMP: Internet Control Message Protocol Main responsibilities of ICMP Error messages are always sent to the original source Error Reporting Destination unreachable Source quench Time exceeded Parameter problems Redirection ICMP always reports error messages to the original source.

Error Reporting Contents of data field for error messages When an ICMP error message is sent, the message always contains the IP header and the first 8 bytes of the IP datagram that caused the ICMP error to be generated.

Error Reporting Destination Unreachable When a router cannot route a datagram or a host cannot deliver a datagram, the datagram is discarded and the router or host send s a destination unreachable message back to the source. Format 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. A router cannot detect all problems that prevent the delivery of a packet There is no flow-control mechanism in the IP protocol.

Error Reporting Destination Unreachable Code Field : the reason for discarding the datagram code Reasons for error 0 Network unreachable 1 Host unreachable 2 Protocol unreachable 3 Port unreachable 4 Fragmentation needed and DF set 5 Source route failed 6 Destination network unknown 7 Destination host unknown 8 Source host isolated 9 Communication with destination network administratively prohibited 10 Communication with destination host administratively prohibited 11 Network unreachable for type of services 12 Host unreachable for type of services

Error Reporting 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. Whenever a router receives a datagram with a time-to-live value of zero, it discards the datagram and sends a time-exceeded message to the original source. 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. Format

Error Reporting Parameter problem Code 0: Main header problem Code 1: Problem in the option field A parameter-problem message can be created by a router or the destination host. Format

Error Reporting Redirection concept When a host send a datagram, which is destined for another network, to the wrong router, the router that receives the datagram will forward the datagram to the correct router. However, to update the routing table of host, it send a redirection message to host. When a new host come up, its routing table has a limited number of entries. It usually knows only a default router, so they can send to wrong router.

Error Reporting Redirection concept A redirection message is sent from a router to host on the same local network. Redirection message format Code 0: Code 1: Code 2: Code 3: Format Network specific Host specific Network specific (specified service) Host specific (specified service)

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.

Query ICMP: Internet Control Message Protocol Diagnose some network problems Query messages Query Echo request & reply Timestamp request & reply Address mask Request & reply Router solicitation & advertisement

Query Echo Request and Reply 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. Echo-request and echo-reply messages can be used by network managers to check the operation of the IP protocol Echo-request and echo-reply messages can test the reachability of a host. this is usually done by invoking the ping command.

Query Timestamp Request and Reply The timestamp-request and timestamp-reply messages can be used to synchronize two clocks in two machines if the exact one-way time duration is known. Timestamp-request and timestamp-reply messages can be used to calculate the round-trip time between a source and a destination machine even if their clocks are not synchronized. Each field is represented by the unit of Miliseconds from midnight in Universal Time 3 timestamp fields(original, receive, transmit) are 32 bit long, (0~4, 294, 967, 295), but a timestamp in this case cannot exceed 86, 400, 000= 24 x 60 x 1000.

Query Timestamp Request and Reply Format Steps Sender create a timestamp-request message Insert the sending time to Original timestamp field Other 2 fields is 0 Receiver create the timestamp-reply message Copy the value of the original timestamp to same field Insert the receiving time of the request message to the receive timestamp

Query Address-Mask Request and Reply When a host want to know about a full IP address which part of address defines the network and subnetwork address and which part corresponds to the host identifier. Masking is needed for diskless station at statr-up time. (BOOTP protocol) Mask-request and mask-reply message format

Query Router solicitation and Advertisement A host the want to send data to a host on outside network needs to know the address of routers connected to its own network. A host can broadcast(or multicast) a router-solicitation message A router or routers that received the solicitation message broadcast their routing information using the router-advertisement message. Router-solicitation message format

Query Router solicitation and Advertisement Router advertisement message format The preference level is used to select a router as the default router. If the preference level is 0, the router is considered the default router. If the preference level is 8000000016, the router should be never selected as the default router.

ICMPv 6 Internet Control Message Protocol Version 6

Comparison of network layers in IPv 4 and IPv 6 ICMPv 6: Internet Control Message Protocol version 6

Message Format Router solicitation and Advertisement General format of ICMPv 6 messages

Error Reporting Router solicitation and Advertisement Error Reporting Destination unreachable Packet too big Time exceeded Parameter problems Redirection

Error Reporting Comparison Error Reporting function between v 4 and v 6 Type of Message V 4 V 6 Destination unreachable Yes Source quench Yes No Packet too big No Yes Time exceeded Yes Parameter problem Yes Redirection Yes

Query ICMPv 6: Internet Control Message Protocol version 6 Diagnose some network problems Query messages Query Echo request & reply Group membership Neighbor solicitation & advertisement Router solicitation & advertisement

Query ICMPv 6: Internet Control Message Protocol version 6 Type of Message V 4 V 6 Echo request and reply Yes Timestamp request and reply Yes No Address mask request and reply Yes No Router solicitation Yes Neighbor solicitation ARP Yes Group membership IGMP Yes