Object Management API (OMAPI)

The Object Management API is an interface on the ISC DHCP server. It provides access to the objects (leases, hosts or groups) stored in its database.

History

The API was introduced by the ISC in version 3 of the DHCP software.

Protocol dependencies

TCP: Typically, OMAPI uses TCP as its transport protocol. The well known TCP port for OMAPI traffic is 7911.

Example traffic

Frame 755 (129 bytes on wire, 129 bytes captured)
Ethernet II, Src: Intel_bf:3b:59 (00:90:27:bf:3b:59), Dst: Cisco_f2:03:78 (00:d0:bc:f2:03:78)
Internet Protocol, Src: 192.168.21.229 (192.168.21.229), Dst: 192.168.1.251 (192.168.1.251)
Transmission Control Protocol, Src Port: 33156 (33156), Dst Port: 7911 (7911), Seq: 3915, Ack: 12060, Len: 63
ISC Object Management API, Opcode: Open
    Authentication ID: 0
    Authentication length: 0
    Opcode: Open (1)
    Handle: 0
    ID: 1804289445
    Response ID: 0
    Message name length: 4
    Message name: type
    Message value length: 5
    Message value: lease
    Message end tag
    Object name length: 10
    Object name: ip-address
    Object value length: 4
    Object value: C0A8093F
    Message end tag

Wireshark

The OMAPI dissector is fully functional.

Preference Settings

There are no preferences for this protocol dissector

Example capture file

SampleCaptures/OMAPI.pcap

Display Filter

A complete list of OMAPI display filter fields can be found in the display filter reference

Show only the OMAPI based traffic:
```
 omapi 
```

Capture Filter

You cannot directly filter OMAPI protocols while capturing. However, if you know the TCP port used (see above), you can filter on that one.

Capture only the OMAPI traffic over the default port (7911):
```
 tcp port 7911 
```

External links

DHCP source code - contains api+protocol description.
man omapi - A OMAPI man page.
man omshell - The simple CLI interface for OMAPI.

Object_Management_API