Extended Echo Reply
ICMP Type 43 Extended Echo Reply responds to an Extended Echo Request (Type 42) with the operational status of the queried network interface. Codes indicate whether the query was valid (0), the query was malformed (1), the interface was not found (2), no matching table entry exists (3), or multiple interfaces matched (4).
Description
ICMP Type 43 Extended Echo Reply is the response to Type 42 Extended Echo Request. The reply code indicates the outcome of the interface lookup: code 0 means the interface was found and its state is reported, codes 1-4 indicate error conditions.
The reply includes L (active), A (IPv4 address exists), B (belongs to point-to-point network), C (is a point-to-point interface) state bits to describe the interface status. Code 2 (No Such Interface) is the most operationally useful: it confirms the queried interface name or index does not exist on the target host.
Code 4 (Multiple Interfaces Satisfy Query) occurs when an IP address is shared across multiple interfaces, making the query ambiguous. In this case the querier should retry with a more specific identifier (interface name or ifIndex).
Common Causes
- –Successful interface status query response (code 0)
- –Extended Echo Request had malformed Interface Identification Object (code 1)
- –Queried interface name or index does not exist on target host (code 2)
- –Interface lookup matched no routing table entry (code 3)
- –Queried IP address is assigned to multiple interfaces (code 4)
Codes
| Code | Name |
|---|---|
| 0 | No Error |
| 1 | Malformed Query |
| 2 | No Such Interface |
| 3 | No Such Table Entry |
| 4 | Multiple Interfaces Satisfy Query |