ICMP offers troubleshooting facility as well as error reporting for the packets
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rest of Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Time Exceed ICMP is when TTL ‘Time to Live’ reach 0
Destination Unreachable is when the packet enter a router that doesnt know how to route the packet.
Redirect : Is when a network condition has change and a different next-hop should be use, the original next hop router will let the host know to use that different path.
ICMP TYPE NUMBERS
The Internet Control Message Protocol (ICMP) has many messages that
are identified by a “type” field.
Type Name Reference
—- ————————- ———
0 Echo Reply [RFC792]
1 Unassigned [JBP]
2 Unassigned [JBP]
3 Destination Unreachable [RFC792]
4 Source Quench [RFC792]
5 Redirect [RFC792]
6 Alternate Host Address [JBP]
7 Unassigned [JBP]
8 Echo [RFC792]
9 Router Advertisement [RFC1256]
10 Router Selection [RFC1256]
11 Time Exceeded [RFC792]
12 Parameter Problem [RFC792]
13 Timestamp [RFC792]
14 Timestamp Reply [RFC792]
15 Information Request [RFC792]
16 Information Reply [RFC792]
17 Address Mask Request [RFC950]
18 Address Mask Reply [RFC950]
19 Reserved (for Security) [Solo]
20-29 Reserved (for Robustness Experiment) [ZSu]
30 Traceroute [RFC1393]
31 Datagram Conversion Error [RFC1475]
32 Mobile Host Redirect [David Johnson]
33 IPv6 Where-Are-You [Bill Simpson]
34 IPv6 I-Am-Here [Bill Simpson]
35 Mobile Registration Request [Bill Simpson]
36 Mobile Registration Reply [Bill Simpson]
37 Domain Name Request [Simpson]
38 Domain Name Reply [Simpson]
39 SKIP [Markson]
40 Photuris [Simpson]
41-255 Reserved [JBP]
Many of these ICMP types have a “code” field. Here we list the types
again with their assigned code fields.
Type Name Reference
—- ————————- ———
0 Echo Reply [RFC792]
Codes
0 No Code
1 Unassigned [JBP]
2 Unassigned [JBP]
3 Destination Unreachable [RFC792]
Codes
0 Net Unreachable “No route to host”
1 Host Unreachable “No route to host”
2 Protocol Unreachable “Connection refused”
3 Port Unreachable “Connection refused”
4 Fragmentation Needed and Don’t Fragment was Set “Message too long”
5 Source Route Failed “No route to host”
6 Destination Network Unknown “No route to host”
7 Destination Host Unknown “No route to host”
8 Source Host Isolated “No route to host”
9 Communication with Destination Network is “No route to host”
Administratively Prohibited “No route to host”
10 Communication with Destination Host is
Administratively Prohibited “No route to host”
11 Destination Network Unreachable for Type of Service “No route to host”
12 Destination Host Unreachable for Type of Service “No route to host”
13 Communication Administratively Prohibited [RFC1812]
14 Host Precedence Violation [RFC1812]
15 Precedence cutoff in effect [RFC1812]
4 Source Quench [RFC792]
Codes
0 No Code
5 Redirect [RFC792]
Codes
0 Redirect Datagram for the Network (or subnet)
1 Redirect Datagram for the Host
2 Redirect Datagram for the Type of Service and Network
3 Redirect Datagram for the Type of Service and Host
6 Alternate Host Address [JBP]
Codes
0 Alternate Address for Host
7 Unassigned [JBP]
8 Echo [RFC792]
Codes
0 No Code
9 Router Advertisement [RFC1256]
Codes
0 No Code
10 Router Selection [RFC1256]
Codes
0 No Code
11 Time Exceeded [RFC792]
Codes
0 Time to Live exceeded in Transit
1 Fragment Reassembly Time Exceeded
12 Parameter Problem [RFC792]
Codes
0 Pointer indicates the error “Protocol not available”
1 Missing a Required Option [RFC1108] “Protocol not available”
2 Bad Length
13 Timestamp [RFC792]
Codes
0 No Code
14 Timestamp Reply [RFC792]
Codes
0 No Code
15 Information Request [RFC792]
Codes
0 No Code
16 Information Reply [RFC792]
Codes
0 No Code
17 Address Mask Request [RFC950]
Codes
0 No Code
18 Address Mask Reply [RFC950]
Codes
0 No Code
19 Reserved (for Security) [Solo]
20-29 Reserved (for Robustness Experiment) [ZSu]
30 Traceroute [RFC1393]
31 Datagram Conversion Error [RFC1475]
32 Mobile Host Redirect [David Johnson]
33 IPv6 Where-Are-You [Bill Simpson]
34 IPv6 I-Am-Here [Bill Simpson]
35 Mobile Registration Request [Bill Simpson]
36 Mobile Registration Reply [Bill Simpson]
39 SKIP [Markson]
40 Photuris [Simpson]
Code
0 Reserved
1 unknown security parameters index
2 valid security parameters, but authentication failed
3 valid security parameters, but decryption failed
