all other options, DHCP local server then appends the unmodified VSA 26-55 DHCP
options to the message and sends the message to the subscriber (DHCP client).
7. The subscriber (DHCP client) is configured with the DHCP options.
8. The following operations occur after the subscriber (DHCP client) receives the DHCP
options:
•
Accounting—The RADIUS client sends Acct-Start and Interim-Accounting requests
to the RADIUS server, including the RADIUS-sourced DHCP options in VSA 26-55.
By default, the DHCP options are included in accounting requests.
•
Renewal—When the subscriber (DHCP client) renews, the cached DHCP options
value is returned in the DHCP renew (or DHCPv6 ACK) message. The originally
assigned DHCP options cannot be modified during a renew cycle.
•
Logout—When the subscriber (DHCP client) logs out, the RADIUS client sends an
Acct-Stop message to the RADIUS server, including the RADIUS-sourced VSA
26-55.
Multiple VSA 26-55 Instances Configuration
VSA 26-55 supports a maximum size of 247 bytes. If your RADIUS-sourced DHCP options
field is greater than 247 bytes, you must break the field up and manually configure multiple
instances of VSA 26-55 for the RADIUS server to return. When using multiple instances
for an options field, you must place the instances in the packet in the order in which the
fragments are to by reassembled by the RADIUS client. The fragments can be of any size
of 247 bytes or less.
BEST PRACTICE: For ease of configuration and management of your DHCP
options, you might want to have one DHCP option per VSA 26-55 instance,
regardless of the size of the option field.
When the RADIUS client returns a reassembled opaque options field in an accounting
request to the RADIUS server, the client uses 247-byte fragments. If you had originally
created instances of fewer than 247 bytes, the returned fragments might not be the same
as you originally configured on the RADIUS server.
NOTE: If you are configuring Steel-Belted Radius (SBR) to support multiple
VSA 26-55 instances, ensure that you specify VSA 26-55 with the RO flags
in the Subscriber Management RADIUS dictionary file. The R value indicates
a multivalued reply attribute and the O value indicates an ordered attribute.
DHCP Options That Cannot Be Centrally Configured
Table 9 on page 36 shows the DHCP options that you must not centrally configure on
the RADIUS server.
35Copyright © 2017, Juniper Networks, Inc.
Chapter 2: DHCP Local Server
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