ICMP Destination Unreachable

ICMP Destination Unreachable

The Destination Unreachable message is an ICMP message which is generated by the host or its inbound gateway[1] to inform the client that the destination is unreachable for some reason. A Destination Unreachable message may be generated as a result of a TCP, UDP or another ICMP transmission. Unreachable TCP ports notably respond with TCP RST rather than a Destination Unreachable type 3 as might be expected.

The error will not be generated if the original datagram has a multicast destination address. Reasons for this message may include: the physical connection to the host does not exist (distance is infinite); the indicated protocol or port is not active; the data must be fragmented but the 'don't fragment' flag is on.

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Type = 3 Code Header Checksum
Empty Next-Hop MTU
IP Header + First 8 Bytes of Original Datagram's Data

The type field (bits 0-7) must be set to 3. The code field (bits 8-15) is used to specify the type of error, and can be any of the following:

Code Description
0 Network unreachable error.
1 Host unreachable error.
2 Protocol unreachable error (the designated transport protocol is not supported).
3 Port unreachable error (the designated protocol is unable to inform the host of the incoming message).
4 The datagram is too big. Packet fragmentation is required but the 'don't fragment' (DF) flag is on.
5 Source route failed error.
6 Destination network unknown error.
7 Destination host unknown error.
8 Source host isolated error (military use only).
9 The destination network is administratively prohibited.
10 The destination host is administratively prohibited.
11 The network is unreachable for Type Of Service.
12 The host is unreachable for Type Of Service.
13 Communication administratively prohibited (administrative filtering prevents packet from being forwarded).
14 Host precedence violation (indicates the requested precedence is not permitted for the combination of host or network and port).
15 Precedence cutoff in effect (precedence of datagram is below the level set by the network administrators).

The Next-Hop MTU field (bits 48-63) contains the MTU of the next-hop network if a code 4 error occurs. The additional data is included to allow the client to match the reply with the request that caused the destination unreachable reply.

References

See also

  • PMTU blackhole

Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • ICMP Destination Unreachable — es un tipo de paquete ICMP cuya función es transportar un mensaje que es generado por un enrutador, y se envía al host de origen, que recibe el mensaje emitido por el enrutador. El mensaje en sí significa que este router considera inalcanzable el …   Wikipedia Español

  • Internet Control Message Protocol — The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet Protocol Suite. It is chiefly used by networked computers operating systems to send error messages mdash;indicating, for instance, that a requested service… …   Wikipedia

  • Maximum transmission unit — In computer networking, the maximum transmission unit (MTU) of a communications protocol of a layer is the size (in bytes) of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a… …   Wikipedia

  • Type of Service — The TOS byte in the IPv4 header has had various purposes over the years, and has been defined in different ways by five different RFCs. (RFC 791, RFC 1122, RFC 1349, RFC 2474, and RFC 3168.) The modern definition of the TOS byte is a six bit… …   Wikipedia

  • Сканер портов — У этого термина существуют и другие значения, см. Сканер. Сканер портов  программное средство, разработанное для поиска хостов сети, в которых открыты нужные порты. Эти программы обычно используются системными администраторами для проверки… …   Википедия

  • UDP flood attack — A UDP flood attack is a denial of service (DoS) attack using the User Datagram Protocol (UDP), a sessionless/connectionless computer networking protocol. Using UDP for denial of service attacks is not as straightforward as with the Transmission… …   Wikipedia

  • Forwarding plane — Cisco VIP 2 40, from an older generation of routers …   Wikipedia

  • Сканирование сети — сетевая атака. Описание Цель этой атаки состоит в том, чтобы выяснить, какие компьютеры подключены к сети и какие сетевые сервисы на них запущены. Первая задача решается путем посылки Echo сообщений протокола ICMP с помощью утилиты ping c… …   Википедия

  • Internet Control Message Protocol — ICMP (Internet Control Message Protocol) Familie: Internetprotokollfamilie Einsatzgebiet: Obligatorischer Zusatz zum Internet Protocol, Fehlermeldungen, Diagnose ICMP im TCP/IP‑Protokollstapel Internet ICMP IPv4 …   Deutsch Wikipedia

  • ICMPv6 — (Internet Control Message Protocol Version 6) Familie: Internetprotokollfamilie Einsatzgebiet: Obligatorischer Zusatz zu IPv6, Fehlermeldungen, Diagnose, Autoconfiguration, Routing Internet Protokolle im TCP/IP Protokollstapel Internet ICMPv6 …   Deutsch Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”