base/protocols/dhcp/main.bro

DHCP

Analyze DHCP traffic and provide a log that is organized around the idea of a DHCP “conversation” defined by messages exchanged within a relatively short period of time using the same transaction ID. The log will have information from clients and servers to give a more complete picture of what happened.

Namespace:DHCP
Imports:base/frameworks/cluster, base/protocols/dhcp/consts.bro
Source File:/scripts/base/protocols/dhcp/main.bro

Summary

Redefinable Options

DHCP::max_txid_watch_time: interval &redef The maximum amount of time that a transation ID will be watched for to try and tie messages together into a single DHCP transaction narrative.

State Variables

DHCP::log_info: DHCP::Info This is a global variable that is only to be used in the :bro::see::DHCP::aggregate_msgs event.

Types

DHCP::Info: record The record type which contains the column fields of the DHCP log.

Events

DHCP::aggregate_msgs: event This event is used internally to distribute data around clusters since DHCP doesn’t follow the normal “connection” model used by most protocols.
DHCP::log_dhcp: event Event that can be handled to access the DHCP record as it is sent on to the logging framework.

Detailed Interface

Redefinable Options

DHCP::max_txid_watch_time
Type:interval
Attributes:&redef
Default:30.0 secs

The maximum amount of time that a transation ID will be watched for to try and tie messages together into a single DHCP transaction narrative.

State Variables

DHCP::log_info
Type:DHCP::Info
Default:
{
   ts=<uninitialized>
   uids={

   }
   client_addr=<uninitialized>
   server_addr=<uninitialized>
   mac=<uninitialized>
   host_name=<uninitialized>
   client_fqdn=<uninitialized>
   domain=<uninitialized>
   requested_addr=<uninitialized>
   assigned_addr=<uninitialized>
   lease_time=<uninitialized>
   client_message=<uninitialized>
   server_message=<uninitialized>
   msg_types=[]
   duration=0 secs
   last_message_ts=<uninitialized>
   msg_orig=<uninitialized>
   client_software=<uninitialized>
   server_software=<uninitialized>
   circuit_id=<uninitialized>
   agent_remote_id=<uninitialized>
   subscriber_id=<uninitialized>
}

This is a global variable that is only to be used in the :bro::see::DHCP::aggregate_msgs event. It can be used to avoid looking up the info record for a transaction ID in every event handler for :bro:see::DHCP::aggregate_msgs.

Types

DHCP::Info
Type:

record

ts: time &log

The earliest time at which a DHCP message over the associated connection is observed.

uids: set [string] &log

A series of unique identifiers of the connections over which DHCP is occurring. This behavior with multiple connections is unique to DHCP because of the way it uses broadcast packets on local networks.

client_addr: addr &log &optional

IP address of the client. If a transaction is only a client sending INFORM messages then there is no lease information exchanged so this is helpful to know who sent the messages. Getting an address in this field does require that the client sources at least one DHCP message using a non-broadcast address.

server_addr: addr &log &optional

IP address of the server involved in actually handing out the lease. There could be other servers replying with OFFER messages which won’t be represented here. Getting an address in this field also requires that the server handing out the lease also sources packets from a non-broadcast IP address.

mac: string &log &optional

Client’s hardware address.

host_name: string &log &optional

Name given by client in Hostname option 12.

client_fqdn: string &log &optional

FQDN given by client in Client FQDN option 81.

domain: string &log &optional

Domain given by the server in option 15.

requested_addr: addr &log &optional

IP address requested by the client.

assigned_addr: addr &log &optional

IP address assigned by the server.

lease_time: interval &log &optional

IP address lease interval.

client_message: string &log &optional

Message typically accompanied with a DHCP_DECLINE so the client can tell the server why it rejected an address.

server_message: string &log &optional

Message typically accompanied with a DHCP_NAK to let the client know why it rejected the request.

msg_types: vector of string &log &default = [] &optional

The DHCP message types seen by this DHCP transaction

duration: interval &log &default = 0 secs &optional

Duration of the DHCP “session” representing the time from the first message to the last.

last_message_ts: time &optional

msg_orig: vector of addr &log &default = [] &optional

(present if policy/protocols/dhcp/msg-orig.bro is loaded)

The address that originated each message from the msg_types field.

client_software: string &log &optional

(present if policy/protocols/dhcp/software.bro is loaded)

Software reported by the client in the vendor_class option.

server_software: string &log &optional

(present if policy/protocols/dhcp/software.bro is loaded)

Software reported by the server in the vendor_class option.

circuit_id: string &log &optional

(present if policy/protocols/dhcp/sub-opts.bro is loaded)

Added by DHCP relay agents which terminate switched or permanent circuits. It encodes an agent-local identifier of the circuit from which a DHCP client-to-server packet was received. Typically it should represent a router or switch interface number.

agent_remote_id: string &log &optional

(present if policy/protocols/dhcp/sub-opts.bro is loaded)

A globally unique identifier added by relay agents to identify the remote host end of the circuit.

subscriber_id: string &log &optional

(present if policy/protocols/dhcp/sub-opts.bro is loaded)

The subscriber ID is a value independent of the physical network configuration so that a customer’s DHCP configuration can be given to them correctly no matter where they are physically connected.

The record type which contains the column fields of the DHCP log.

Events

DHCP::aggregate_msgs
Type:event (ts: time, id: conn_id, uid: string, is_orig: bool, msg: DHCP::Msg, options: DHCP::Options)

This event is used internally to distribute data around clusters since DHCP doesn’t follow the normal “connection” model used by most protocols. It can also be handled to extend the DHCP log.

:bro:see::DHCP::log_info.

DHCP::log_dhcp
Type:event (rec: DHCP::Info)

Event that can be handled to access the DHCP record as it is sent on to the logging framework.

Copyright 2016, The Bro Project. Last updated on June 15, 2018. Created using Sphinx 1.7.2.