DHCP Relay Agent Information Option (Option 82)
The DHCP relay agent information option (option 82) enables you to include additional useful information in the client-originated DHCP packets that the DHCP relay forwards to a DHCP server. You can configure the option 82 support globally or for a named group of interfaces. For more information, read this topic.
Using DHCP Relay Agent Option 82 Information
Subscriber management enables you to configure the DHCP relay agent to include additional option 82 information in the DHCP packets that the relay agent receives from clients and forwards to a DHCP server. The DHCP server uses the additional information to determine the IP address to assign to the client. The server might also use the information for other purposes—for example, to determine which services to grant the client, or to provide additional security against threats such as address spoofing. The DHCP server sends its reply back to the DHCP relay agent, and the agent removes the option 82 information from the message and forwards the packet to the client.
To configure support for the DHCP relay agent information
option 82, you use the relay-option-82 statement. You can
configure the DHCP relay agent to include the following suboptions
in the packet the relay agent sends to the DHCP server:
Agent Circuit ID (suboption 1)—An ASCII string that identifies the interface on which the client DHCP packet is received.
Note:If
relay-option-82is configured, but none of the attributes underrelay-option-82(that is,circuit-id|remote-id|server-id-override) are explicitly configured, then the default behavior is for the circuit-id (that is, suboption 1) to always be included in the option-82 value. This is true whether or not thevendor-specificattribute underrelay-option-82is configured.Agent Remote ID (suboption 2)—An ASCII string assigned by the DHCP relay agent that securely identifies the client.
You can configure the option 82 support globally or for a named group of interfaces.
To restore the default behavior, in which option 82 information
is not inserted into DHCP packets, you use the delete relay-option-82 statement.
The DHCPv6 relay agent provides similar Agent Circuit ID and Agent Remote ID support for DHCPv6 clients. For DHCPv6, subscriber management uses DHCPv6 option 18 to include the circuit ID in the packets that the relay agent sends to a DHCPv6 server, and option 37 to include the remote ID in the packets. See DHCPv6 Relay Agent Options.
The following sections describe the option 82 operations you can configure:
- Configuring Option 82 Information
- Overriding Option 82 Information
- Including a Prefix in DHCP Options
- Including a Textual Description in DHCP Options
Configuring Option 82 Information
You use the relay-option-82 statement to configure
the DHCP relay agent to insert option 82 information in DHCP packets
that the relay agent receives from clients and forwards to a DHCP
server. When you configure option 82, you can include one of the suboption
statements to specify the type of information you want to include
in the DHCP packets. If you configure option 82 without including
one of the suboption statements, the Agent Circuit ID option is included
by default. Use the circuit-id statement to include the
Agent Circuit ID (suboption 1) in the packets, or the remote-id statement to include the Agent Remote ID (suboption 2).
You can optionally configure DHCP relay agent to include
a prefix or the interface description as part of the suboption information.
If you specify the circuit-id or remote-id statement
without including any of the optional prefix, use-interface-description, use-vlan-id, include-irb-and-l2, or no-vlan-interface-name statements, the format of the Agent
Circuit ID or Agent Remote ID information for Fast Ethernet (fe),
Gigabit Ethernet (ge), and integrated routing and bridging (irb) interfaces
is one of the following, depending on your network configuration:
For Fast Ethernet or Gigabit Ethernet interfaces that do not use VLANs, stacked VLANs (S-VLANs), or bridge domains:
(fe | ge)-fpc/pic/port.subunit
Note:For remote systems, the subunit is required and is used to differentiate an interface.
For Fast Ethernet or Gigabit Ethernet interfaces that use VLANs:
(fe | ge)-fpc/pic/port:vlan-id
For Fast Ethernet or Gigabit Ethernet interfaces that use S-VLANs:
(fe | ge)-fpc/pic/port:svlan-id-vlan-id
Integrated routing and bridging (IRB) provides simultaneous support for Layer 2 bridging and Layer 3 IP routing on the same interface. IRB enables you to route local packets to another routed interface or to another bridging domain that has a Layer 3 protocol configured.
The interface to bridge domain relationship might be implicit (the interface is mapped to the bridge domain by the system based on the VLAN tag) or explicit (the interface is mapped to the bridge domain by configuring it in the bridge domain definition). For the explicit case, tagging might not be relevant for the mapping.
In the case of an IRB interface, the format displays the Layer 2 interface instead of the IRB interface along with the bridge domain name. For IRB interfaces (or other pseudo devices) the default format is as follows:
IRB interfaces that use bridge domains but do not use VLANs or S-VLANs:
(fe | ge)-fpc/pic/port.subunit:bridge-domain-name
IRB interfaces that use VLANs:
(fe | ge)-fpc/pic/port.subunit:vlan-name
To include the IRB interface name with the Layer 2 interface
name, configure the include-irb-and-l2 statement. The format
is as follows:
IRB interfaces that use bridge domains but do not use VLANs or S-VLANs:
(fe | ge)-fpc/pic/port:bridge-domain-name+irb.subunit
IRB interfaces that use VLANs:
(fe | ge)-fpc/pic/port:vlan-name+irb.subunit
To include only the IRB interface name without the Layer 2 interface
and bridge domain or VLAN, configure the no-vlan-interface-name statement. The format is as follows:
irb.subunit
To enable insertion of option 82 information:
Overriding Option 82 Information
You can configure the DHCP relay agent to add or remove the DHCP relay agent information option (option 82) in DHCP packets.
This feature causes the DHCP relay agent to perform one of the following actions, depending on the configuration:
If the DHCP relay agent is configured to add option 82 information to DHCP packets, it clears the existing option 82 values from the DHCP packets and inserts the new values before forwarding the packets to the DHCP server.
If the DHCP relay agent is not configured to add option 82 information to DHCP packets, it clears the existing option 82 values from the packets, but does not add any new values before forwarding the packets to the DHCP server.
To override the default option 82 information in DHCP packets destined for a DHCP server:
Including a Prefix in DHCP Options
When you configure the DHCP relay agent to include DHCP options in the packets that the relay agent sends to a DHCP server, you can specify that the relay agent add a prefix to the DHCP option. You can add a prefix to the following DHCP options:
DHCPv4 option 82 Agent Circuit ID (suboption 1)
DHCPv4 option 82 Agent Remote ID (suboption 2)
DHCPv6 option 18 Relay Agent Interface-ID
DHCPv6 option 37 Relay Agent Remote-ID
The prefix is separated from the DHCP option information
by a colon (:), and it can include any combination of the host-name, logical-system-name, and routing-instance-name options. The DHCP relay agent obtains the values for the host-name, logical-system-name, and routing-instance-name as follows:
If you include the
host-nameoption, the DHCP relay agent uses the hostname of the device configured with thehost-namestatement at the[edit system]hierarchy level.If you include the
logical-system-nameoption, the DHCP relay agent uses the logical system name configured with thelogical-systemstatement at the[edit logical-system]hierarchy level.If you include the
routing-instance-nameoption, the DHCP relay agent uses the routing instance name configured with therouting-instancestatement at the[edit routing-instances]hierarchy level or at the[edit logical-system logical-system-name routing-instances]hierarchy level.
If you include the hostname and either or both of the logical system name and the routing instance name in the prefix, the hostname is followed by a forward slash (/). If you include both the logical system name and the routing instance name in the prefix, these values are separated by a semicolon (;).
The following examples show several possible formats
for the DHCP option information when you specify the prefix statement for Fast Ethernet (fe) or Gigabit Ethernet (ge) interfaces
with S-VLANs.
If you include only the hostname in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
hostname:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
If you include only the logical system name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
logical-system-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
If you include only the routing instance name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
routing-instance-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
If you include both the hostname and the logical system name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
host-name/logical-system-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
If you include both the logical system name and the routing instance name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
logical-system-name;routing-instance-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
If you include the hostname, logical system name, and routing instance name in the prefix for Fast Ethernet or Gigabit Ethernet interfaces with S-VLANs:
host-name/logical-system-name;routing-instance-name:(fe | ge)-fpc/pic/port:svlan-id-vlan-id
For Fast Ethernet or Gigabit Ethernet interfaces that use VLANs
but not S-VLANs, only the vlan-id value
appears in the DHCP option format.
(DHCPv4) To configure a prefix with the option 82 information:
(DHCPv6) To use a prefix with the DHCPv6 option 18 or option 37 information:
Specify that you want to configure DHCPv6 relay agent support.
[edit forwarding-options dhcp-relay] user@host# edit dhcpv6
Configure DHCPv6 relay agent to insert option 18 (Relay Agent Interface-ID), option 37 (Relay Agent Remote-ID), or both.
To configure option 18:
[edit forwarding-options dhcp-relay dhcpv6] user@host# edit relay-agent-interface-id
To configure option 37:
[edit forwarding-options dhcp-relay dhcpv6] user@host# edit relay-agent-remote-id
Specify that the prefix is included in the option information. In this example, the prefix includes the hostname and logical system name
To include the prefix with option 18:
[edit forwarding-options dhcp-relay dhcpv6 relay-agent-interface-id] user@host# set prefix host-name logical-system-name
To include the prefix with option 37:
[edit forwarding-options dhcp-relay dhcpv6 relay-agent-remote-id] user@host# set prefix host-name logical-system-name
Including a Textual Description in DHCP Options
By default, when DHCP relay agent inserts option information in the packets sent to a DHCP server, the options include the interface identifier. However, you can configure the DHCP relay agent to include the textual description that is configured for the interface instead of the interface identifier. You can use the textual description for either the logical interface or the device interface.
You can include the textual interface description in the following DHCP options:
DHCPv4 option 82 Agent Circuit ID (suboption 1)
DHCPv4 option 82 Agent Remote ID (suboption 2)
DHCPv6 option 18 Relay Agent Interface-ID
DHCPv6 option 37 Relay Agent Remote-ID
The textual description is configured separately, using the description statement at the [edit interfaces interface-name] hierarchy level. If you specify
that the textual description is used and no description is configured
for the interface, DHCP relay defaults to using the Layer 2 interface
name.
In the case of integrated routing and bridging (IRB) interfaces, the textual description of the Layer 2 interface is used instead of the textual description of the IRB interface. If there is no description configured, the Layer 2 logical interface name is used.
For IRB interfaces, the option 82 field must be able to uniquely identify the incoming interface based on either the Agent Circuit ID or Agent Remote ID . You can modify the information in the textual interface description to match the raw IFD (physical interface without a subunit) name and configure the option 82 field to use the interface description.
You can use the textual description with the following DHCP options:
DHCPv4 Option 82 Agent Circuit ID (suboption 1)
DHCPv4 Option 82 Agent Remote ID (suboption 2)
DHCPv6 Relay Agent Interface-ID (option 18)
DHCPv6 Relay Agent Remote-ID (option 37)
(DHCPv4) To configure the DHCP relay option 82 suboption to include the textual interface description:
(DHCPv6) To configure the DHCPv6 option 18 or option 37 to include the textual interface description:
Specify that you want to configure DHCPv6 relay agent support.
[edit forwarding-options dhcp-relay] user@host# edit dhcpv6
Configure DHCPv6 relay agent to insert option 18 (Relay Agent Interface-ID), option 37 (Relay Agent Remote-ID), or both.
To configure option 18:
[edit forwarding-options dhcp-relay dhcpv6] user@host# edit relay-agent-interface-id
To configure option 37:
[edit forwarding-options dhcp-relay dhcpv6] user@host# edit relay-agent-remote-id
Specify that the textual description is included in the option information. In the following example, the option information includes the description used for the device interface.
To include the textual description in option 18:
[edit forwarding-options dhcp-relay dhcpv6 relay-agent-interface-id] user@host# set use-interface-description device
To include the textual description in option 37:
[edit forwarding-options dhcp-relay dhcpv6 relay-agent-remote-id] user@host# set use-interface-description device
See Also
How DHCP Relay Agent Uses Option 82 for Auto Logout
Table 1 indicates how the DHCP relay agent determines the option 82 value used for the client auto logout feature. Depending on the configuration settings, DHCP relay agent takes the action indicated in the Action Taken column.
DHCP Relay Agent Configuration Settings |
|||||
|---|---|---|---|---|---|
DHCP Relay Configured with Option 82 |
Discover Packet Contains Option 82 |
Override “trust-option- 82” |
Override “always-write- option-82” |
giaddr in non-snooped packet |
Action Taken |
No |
No |
– |
– |
– |
No secondary search performed |
No |
Yes |
Yes |
– |
– |
Use option 82 from packet |
No |
Yes |
No |
– |
Zero |
Drop packet |
No |
Yes |
No |
– |
Non-zero |
Use option 82 from packet |
Yes |
No |
– |
– |
– |
Use configured option 82 |
Yes |
Yes |
No |
– |
Zero |
Drop packet |
Yes |
Yes |
No |
No |
Non-zero |
Use option 82 from packet |
Yes |
Yes |
No |
Yes |
Non-zero |
Overwrite the configured option 82 |
Yes |
Yes |
Yes |
No |
– |
Use option 82 from packet |
Yes |
Yes |
Yes |
Yes |
– |
Overwrite the configured option 82 |
Enable Processing of Untrusted Packets So Option 82 Information Can Be Used
By default, the DHCP relay agent treats client packets with a giaddr of 0 (zero) and option 82 information as if the packets originated at an untrusted source, and drops them without further processing. You can override this behavior and specify that the DHCP relay agent process DHCP client packets that have a giaddr of 0 (zero) and contain option 82 information.
To configure DHCP relay agent to trust option 82 information:
Check if Your Device Support DHCP Option-82
To configure a switch with DHCP relay in forward-only mode, check whether your DHCP server supports DHCP Option 82.
Use the procedures in Table 2 to confirm the support of Option-82 or required workaround.
Problem |
How to Verify ? |
Solution |
|---|---|---|
Verify if your DHCP server supports DHCP Option 82. |
Use the If the DHCP Offer packet dropped because of Option-82 not included, you will receive the message like: Feb 25 15:41:13.577519 [MSTR][NOTE] [default:default][RLY][INET][irb.6] jdhcpd_packet_handle: BOOTPREPLY could not find client table entry |
To fix the issue:
|
Example: The DHCP Server in MS Windows Server 2019 fully supports Option 82, where as version 2016 has partial support.
See Also
Managing Your DHCP PXE/BOOTP Servers That Do Not Support Option-82
Some PXE or BOOTP servers do not support Option-82, that is, their DHCP Offer messages do not include the Option-82 value added by the DHCP Relay. As a result, the DHCP Relay will drop the DHCP Offer and the PXE/BOOTP client will not be able to complete its boot sequence.
Following are the possible solution to resolve this issue:
Solution 1: Upgrade to a PXE Server that supports Option-82
Solution 2: Host the PXE server with a DHCP Server
Ensure that the DHCP Server (that supports Option-82) run together with the PXE server.
Configure an Option-60 on the DHCP Server.
Use the following CLI to configure Option-60 an a Microsoft WS DHCP Server:
netsh dhcp server dhcp-server-address add optiondef 60 ClientIdentifier STRING 0 PXEClient
Activate the option in the user interface of the DHCP server.
This way, the PXE/BOOTP clients will receive proper DHCP Offer with Option-60 “PXEClient” and will reach the PXE server at the same IP address of the DHCP Server.
Solution 3: Include Option-60 and Option-43 DHCP Server Message
If the PXE Server is not hosted together with the DHCP Server, you need the DHCP Server to send an Option-43 also in its DHCP Offer. The Option-43 provides the IP address of the PXE server. Note that, the older PXE or BOOTP clients might ignore Option-43 and will therefore try to get the software from the DHCP Server. Enter the Option-43 in the DHCP Server configuration in a hexadecimal mode.
For is a sample option-43 message:
06 01 07 08 07 00 01 01 0A 0B 0C 0D 09 0B 00 01 09 53 65 72 76 65 72 50 58 45 0A 02 00 53
The above message indicates the following information to the PXE client:
Disable broadcast and multicast discovery
Accept only the PXE Server provided in this text
PXE Server IP is 10.11.12.13 (see the bytes '0A 0B 0C 0D' in the above text)
Boot menu on the PXE client (to present to the end user):
just one line, “ServerPXE”
Autoselect the first Boot option, prompt “S”, no timeout (that is, immediately boot unless you press F8)
DHCP Packets on Non-Configured Interfaces
Once you enable DHCP-Relay on the MX Series routers, QFX or EX Series switches, the DHCP Snooping feature gets enabled and all DHCP packets incoming through any interface (both configured and unconfigured interface) of the device are analyzed. The interfaces that are not listed under the DHCP configuration are considered ‘unconfigured’.
Depending on the configuration, DHCP packets received on unconfigured interfaces are dropped.
If the DHCP packets are dropped on ‘unconfigured’ interface, you will receive the following message:
May 25 18:26:31.796241 [MSTR][NOTE] [default:default][RLY][INET][irb.82] jdhcpd_packet_handle: BOOTPREQUEST irb.82 arrived on unconfigured interface DISCOVER, flags 23, config 0x0
See Also
Example: Configure DHCP Relay in Forward Only Mode
The example shows how to configure a “stateless” (“forward-only”) DHCP Relay on Enhanced Layer 2 Software (ELS) EX Series and QFX Series switches. If your switch runs software that does not support ELS, see Configuring Interface Ranges. For ELS details, see Using the Enhanced Layer 2 Software CLI.
Requirements
This example uses the following hardware and software components:
QFX or EX Series Switches (ELS mode).
Junos OS Release 18.4R3.
Before you configure forward-only DHCP relay on EX Series and QFX Series switches, lets understand about Option 82 support on DHCP.
To verify whether your device supports DHCP Option-82, see Check if Your Device Support DHCP Option-82.
The following messages from the DHCP server include a copy of the Option 82 information on sent by the DHCP Relay in the Discover and Request messages:
Offer
Acknowledgement (ACK)
Negative acknowledgment (NACK)
The DHCP relay discards any OFFER, ACK, and NACK messages that do not include a valid Option 82 information.
On how to avoid dropping of DHCP offer message when PXE or BOOTP servers do not support Option-82, see Managing Your DHCP PXE/BOOTP Servers That Do Not Support Option-82.
Overview
In this example, we are configuring a switching device to act as DHCP relay agent by completing the following steps:
Add a set of DHCP server IP addresses configured as active server groups.
Configure the option 82 support for a named group of interfaces.
After you configure the example, the DHCP relay agent includes option 82 information in the DHCP packets that it receives from the clients and forwards to the DHCP server.
Configuration
To configure a forward-only DHCP relay agent on a ELS supported EX or QFX switches, perform these tasks:
CLI Quick Configuration
To quickly configure this example, copy the
following commands, paste them in a text file, remove any line breaks,
change any details necessary to match your network configuration,
and then copy and paste the command into the CLI at the [edit] hierarchy level.
set forwarding-options dhcp-relay server-group SV1 dhcp-server-1-address set forwarding-options dhcp-relay server-group SV2 dhcp-server-2-address set forwarding-options dhcp-relay active-server-group SV1 set forwarding-options dhcp-relay group DHCP-FO forward-only set forwarding-options dhcp-relay group DHCP-FO relay-option-82 circuit-id use-interface-description device set forwarding-options dhcp-relay group DHCP-FO interface interface1 set forwarding-options dhcp-relay group DHCP-FO interface interface2
Configure forward-only' DHCP Relay Agent
Step-by-Step Procedure
To configure forward-only DHCP relay:
Specify the name of the server group, SV1 and SV2.
[edit forwarding-options dhcp-relay] user@host#
set server-group SV1user@host#set server-group SV2Add the IP addresses of the DHCP servers belonging to the group.
[edit forwarding-options dhcp-relay] user@host#
set server-group SV1 dhcp-server-1-addressuser@host#set server-group SV2 dhcp-server-2-address(Optional) In enterprise scenario, you can use the Preboot Execution Environment (PXE) or BOOTP for a PC (or other devices) to get its Junos OS from a server.
If you want to enable BOOTP support when the switch is configured to be a DHCP relay agent, enter the following statement:
[edit forwarding-options dhcp-relay] user@host#
set overrides bootp-supportAdd a DHCP or PXE Servers to the DHCP Servers group
[edit forwarding-options dhcp-relay] user@host#
server-group SV1 dhcp-server-3-address
Apply the server group as an active server group.
[edit forwarding-options dhcp-relay] user@host#
set active-server-group SV1Define DHCP-FO as interface group on your switching device acting as DHCP relay. Configure:
[edit forwarding-options dhcp-relay] user@host#
set group DHCP-FO forward-onlyAdd a list of interfaces to the interface group.
[edit forwarding-options dhcp-relay] user@host#
set group DHCP-FO interface interface1user@host#set group DHCP-FO interface interface2Set relay option 82 to interfaces and specify Agent circuit ID. Agent Circuit ID identifies the interface on which the client DHCP packet is received. When you configure circuit ID, the include the textual interface description in the message.
[edit forwarding-options dhcp-relay] user@host#
set group DHCP-FO group relay-option-82 circuit-id use-interface-description device
Results
From configuration mode, confirm the results of your
configuration by issuing the show statement at the [edit forwarding-options] hierarchy level. If the output does
not display the intended configuration, repeat the configuration instructions
in this example to correct it.
[edit forwarding-options]
user@host> show
dhcp-relay {
server-group {
SV1 {
dhcp-server-1-address;
}
SV2 {
dhcp-server-2-address;
}
}
active-server-group SV1;
group DHCP-FO {
relay-option-82 {
circuit-id {
use-interface-description device;
}
}
forward-only;
interface interface1;
interface interface2;
}
}
If you are done configuring the device, enter commit from configuration mode.
Verification
Verify if the messages from the DHCP server includes a copy of the Option 82 information sent by the DHCP relay.
Verifying the Offer message with Option-82
Purpose
Verify the “forward-only” DHCP Relay by enabling the dhcp traceoptions on the DHCP Relay.
Action
Receive the output of the tracing operation in the specified file.
user@host# set system processes dhcp-service traceoptions file dhcp_logfile size 10m user@host# set system processes dhcp-service traceoptions level all user@host# set system processes dhcp-service traceoptions flag all Feb 25 15:41:11.454186 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_io_process_ip_packet: LOCAL: recv pkt; sa 10.42.6.20; da 10.42.59.251; src_port 67; dst_port 67; len 410 Feb 25 15:41:11.454218 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP from == 10.42.6.20, port == 67 ]-- Feb 25 15:41:11.454228 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP size == 410, op == 2 ]-- Feb 25 15:41:11.454250 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP flags == 8000 ]-- Feb 25 15:41:11.454271 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP htype == 1, hlen == 6 ]-- Feb 25 15:41:11.454292 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP hops == 0, xid == e50f52a1 ]-- Feb 25 15:41:11.454313 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP secs == 0, flags == 8000 ]-- Feb 25 15:41:11.454347 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP ciaddr == 0.0.0.0 ]-- Feb 25 15:41:11.454428 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP yiaddr == 10.42.58.21 ]-- Feb 25 15:41:11.454461 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP siaddr == 10.42.6.20 ]-- Feb 25 15:41:11.454472 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP giaddr == 10.42.59.251 ]-- Feb 25 15:41:11.454486 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP chaddr == 34 48 ed 27 e2 29 00 00 00 00 00 00 00 00 00 00 ]-- Feb 25 15:41:11.454508 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP sname == ]-- Feb 25 15:41:11.454535 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ DHCP/BOOTP file == ]-- Feb 25 15:41:11.454560 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 53, len 1, data DHCP-OFFER ]-- Feb 25 15:41:11.454603 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 1, len 4, data ff ff fc 00 ]-- Feb 25 15:41:11.454616 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 58, len 4, data 00 05 46 00 ]-- Feb 25 15:41:11.454638 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 59, len 4, data 00 09 3a 80 ]-- Feb 25 15:41:11.454675 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 51, len 4, data 00 0a 8c 00 ]-- Feb 25 15:41:11.454701 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 54, len 4, data 0a 2a 06 14 ]-- Feb 25 15:41:11.454724 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 3, len 4, data 0a 2a 3b fe ]-- Feb 25 15:41:11.454748 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 4, len 8, data 0a 2a 01 64 0a 2a 06 64 ]-- Feb 25 15:41:11.454778 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 6, len 8, data 0a 2a 01 64 0a 2a 06 64 ]-- Feb 25 15:41:11.454805 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 15, len 15, data 6c 69 73 65 63 2e 69 6e 74 65 72 6e 61 6c 00 ]-- Feb 25 15:41:11.454829 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 42, len 8, data 0a 2a 01 64 0a 2a 06 64 ]-- Feb 25 15:41:11.454858 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 128, len 29, data 61 74 73 65 2d 65 6d 70 69 72 75 6d 31 2e 6c 69 73 65 63 2e 69 6e 74 65 72 6e 61 6c 00 ]-- Feb 25 15:41:11.454888 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 129, len 29, data 61 74 73 65 2d 65 6d 70 69 72 75 6d 31 2e 6c 69 73 65 63 2e 69 6e 74 65 72 6e 61 6c 00 ]-- Feb 25 15:41:11.454902 [MSTR][DEBUG][default:default][RLY][INET][irb.56] --[ OPTION code 82, len 19, data 01 11 49 52 42 2d 69 72 62 2e 35 36 3a 61 65 33 30 2e 30 ]-- Feb 25 15:41:11.454924 [MSTR][INFO] [default:default][RLY][INET][irb.56] --[ OPTION code 255, len 0 ]-- Feb 25 15:41:11.454939 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_find_client_from_server_pdu: Using yiaddr from BOOTPREPLY for lookup Feb 25 15:41:11.454962 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_platform_client_v4_app_get_l3_index: safd is not client type Feb 25 15:41:11.454992 [MSTR][DEBUG] client_key_compose: Composing key (0xb294380) for cid_l 0, cid NULL, mac 34 48 ed 27 e2 29, htype 1, subnet 10.42.59.251, ifindx 0, opt82_l 0, opt82 NULL Feb 25 15:41:11.455016 [MSTR][DEBUG] client_key_compose: Successfully composed CK_TYPE_HW_ADDR_ON_SUBNET (2) client key object. Feb 25 15:41:11.455028 [MSTR][DEBUG] client_key_print: key_type CK_TYPE_HW_ADDR_ON_SUBNET (2): subnet 10.42.59.251, MAC htype 1, Addr 34 48 ed 27 e2 29 Feb 25 15:41:11.455050 [MSTR][DEBUG] client_key_print: key_type CK_TYPE_HW_ADDR_ON_SUBNET (2) other fields: subnet 10.42.59.251, ifindex 0, opt82_len 0, - Feb 25 15:41:11.455081 [MSTR][INFO] [default:default][RLY][INET][irb.56] jdhcpd_process_forward_only_or_drop: Safd irb.56 in routing context default:default - forward only or drop processing Feb 25 15:41:11.455114 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_option_strip_relay_info: Removing option-82 Feb 25 15:41:11.455124 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_option_strip_relay_info: Length of option 82 = 21 bytes Feb 25 15:41:11.455146 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_option_strip_relay_info: Moving 2 bytes, which were after option 82 and parse again Feb 25 15:41:11.455169 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_process_forward_only_or_drop: Safd irb.56 in routing context default:default - config supports fwd only relaying packet Feb 25 15:41:11.455193 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_process_forward_only_or_drop: Result of forward-only: packet_consumed Yes, packet_dropped No, message_type OFFER Feb 25 15:41:11.455217 [MSTR][DEBUG][default:default][RLY][INET][irb.56] jdhcpd_relay_forward_only_packet: Broadcast BOOTPREPLY OFFER for 10.42.58.21 on safd irb.56
You can use the following commands to search for problems in the DHCP traceoptions log file (in this example, ‘dhcp_logfile’).
To get an overview of most common problems, use:
user@host> show log dhcp_logfile | match "dropp|fail|unconf" | except "packet_dropped No"
To investigate a specific problem, use:
user@host> show log dhcp_logfile | find " arrived on unconfigured interface"
The
findcommand is similar to Linuxlesscommand. It will reach the first entry in the log and allow you to scroll up/down the message.
(Optional) To query the traceoptions logs on a Linux sever (or from the Junos shell), you can use both the following commands:
user@host> egrep -i "dropp|fail|unconf" dhcp_logfile | egrep -v "packet_dropped No" | more
user@host> egrep -i -b 5 " arrived on unconfigured interface" dhcp_logfile | more
Meaning
The above sample confirms that the messages from the DHCP server includes a copy of the Option 82 information sent by the DHCP relay and the sample also displays the textual description of the interface.