February 2000
Intermediate to advanced
464 pages
15h 57m
English
Content preview from Internet Core Protocols: The Definitive GuideBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Name
Destination Unreachable
Synopsis
Destination Unreachable means that the destination network, host, or port number specified in the IP datagram was unreachable. This could be a result of a variety of factors, ranging from a router being unable to find a path to the remote system, to the network refusing to accept connections from this particular sender, among many other factors.
- ICMP Message Type
The Message Type for Destination Unreachable is 3.
- ICMP Message Codes
Destination Unreachable makes extensive use of the Code field. RFC 792 defined six different possible failure codes, numbered through 5. This list was supplemented by RFC 1122, which added seven additional codes (6 through 12). Finally, RFC 1812 added three more codes (13 through 15), but also declared codes 8 through 10 as either obsolete or inappropriate for non-military usage (for this reason, they are not documented in this book).Table 5.4 lists the Codes currently used by Destination Unreachable
Table 5.4. Codes for Destination Unreachable and Their MeaningCode
Meaning
0
Network Unreachable
1
Host Unreachable
2
Protocol Unreachable
3
Port Unreachable
4
Fragmentation Required but DF Bit Is Set
5
Source Route Failed
6
Destination Network Unknown
7
Destination Host Unknown
8
Source Host Isolated (obsolete)
9
Destination Network Administratively Prohibited (obsolete)
10
Destination Host Administratively Prohibited (obsolete)
11
Destination Network Unreachable for Type-of-Service
12
Destination Host Unreachable for Type-of-Service
13
Communication ...
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