Droms R. The DHCP handbook
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activating scopes on DHCP servers, 221
ACTIVE state, IP address binding, 163-164
add operator (DNS), 485
Add Server command (Action menu), 205
Add/Remove Programs option (Control Panel),
203-205
adding
network services
pre-DHCP development, 6
via DHCP, 11
reservations to Microsoft DHCP server,
454-455
scopes
to existing superscopes (DHCP servers),
214
Microsoft DHCP server, 443
address pools
depletion monitors, 334
usage monitors, 334
Address Resolution Protocol (ARP), 12
packet transmission, 268-269
TCP/IP data link layer, 45-46
address statement, failover peer declaration, 473
addresses
allocation, 342
class membership, 343-344
class-based, 344-346
pools, 343
IPv6 (Internet Protocol version 6)
colon hexadecimal, 432
interface identifiers, 434
loopback, 433
prefix length, 432
scopes, 433
unicast, 432
lifetime management (DHCPv6), 437
Administrative tools command (Programs
menu), 205
all clients permit, pool declaration, 467
all subnets local option (TCP/IP stack configura-
tion parameters), 139
allocating IP addresses, 342
assignment of, 195
automatic method, 15
BOOTREQUEST messages, 194-195
by class, 344-346
by class membership, 343-344
DHCP server agent, 9
DHCPDISCOVER messages, 194-195
DHCPREQUEST message, 196-197
dynamic allocation, 193-194
dynamic method, 15
failover protocol, 161
hybrid methods, 15-16
pools, 343
pre-DHCP development, 4-5
static allocation, 194
static method, 15
allow known clients directive, 344
allow unknown clients directive, 344
allow|deny|ignore statements, 486
booting flag, 486
bootp flag, 486
client-updates flag, 487
declines flag, 487
duplicates flag, 486
always-broadcast statement, 491
always-reply-rfc1048 statement, 490
and operator (Boolean), 480
Apple MacOS X DHCP client
configuring, 374-378
controlling from command line, 376-378
application layer (TCP/IP), client/server model,
54
architecture, specifying to DHCP servers, 29-32
activating scopes on DHCP servers546
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ARP (Address Resolution Protocol), 12
packet transmission, 268-269
TCP/IP data link layer, 45-46
ARP cache timeout option (link layers configura-
tion parameters), 141
arrays, option definition, 498
assigning IP addresses, 9-10
allocations, 195
DHCP servers, 321-322
dynamically (DHCP), 60
ISC DHCP server configuration, 244
static allocation of clients, 280-281
authentication, 157
DHCP messages, 94
goals, 95
key-hashing, 95-101
plain-text tokens, 95-96
versus access control lists, 288
Authentication Token Protocol, DHCP messages,
96
authoritative name server (DHCP), 188-189
configuring, 253-257
authoritative statement, 254, 489-490
autoconfiguration addresses, 357
Automated Private IP Addressing (APIPA), 356
automatic IP addresses
allocation, 15, 286
BOOTP devices, assigning, 324-325
automatic startups, ISC DHCP server
configuring, 247-249
shell scripts, 248
startup files, 249
AUTORETRIES option (NetWare Directory
Services), 154
AUTORETRY SECS option (NetWare Directory
Services), 154
available addresses, DHCP servers, 208-209
B
backing store relationship (failovers), 301-303
backup IP addresses, 161
BACKUP state, IP address binding, 163-164
binary-to-ascii operator (data), 481
binding
IP addresses
ABANDONED state, 163-164
ACTIVE state, 163-164
BACKUP state, 163-164
EXPIRED state, 163-164
FREE state, 163-164
RELEASED state, 163-164
RESET state, 163-164
update conflicts, BNDUPD message (failover
protocol), 173
BNDUPD message, binding update conflicts
(failover protocol), 173
Boolean expressions, 478
Boolean operators
=, 479
and, 480
exists, 480
known, 480
not, 480
or, 480
static, 479
bootfile name option (DHCP-specific options),
130
bootfile size option (host configuration parame-
ters), 134
BOOTP (Bootstrap Protocol), 7, 65-67
clients, server configuration support/non-
support, 423
file, configuring (Microsoft DHCP server), 448
forerunner of DHCP, 7
messages versus DHCP messages, 69, 80-81
BOOTP 547
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BOOTP devices
interoperation with DHCP servers (RFC 1534),
322
support strategies, 322
automatic address assignments for clients,
324-325
elimination, 322-323
separating BOOTP server and DHCP server,
325
static address assignments for clients,
323-324
BOOTP Table dialog box, 448
BOOTREQUEST message, IP address allocation,
194-195
Bootstrap Protocol. See BOOTP
BOUND state, 104-105, 357
broadcast address option (TCP/IP stack configu-
ration parameters), 139
BROADCAST bit, 420-422
broadcast flags, DHCP messages, server
responses to clients, 86
broadcast messages (DHCP), 84
broadcast traffic, resource starvation, 294
broadcasting lease extensions, 118
building ISC DHCP server distributions, 227-228
C
cable modem networks, shared network pitfalls,
270
caching server (DHCP), 188-189
chaddr field, DHCP fixed-format message sec-
tion, 71
ciaddr field, DHCP fixed-format message section,
71
CIDR (classless internet domain routing), 49, 140
Cisco DHCP relay agent, 262-263
Class A IP addresses, 48-49
Class B IP addresses, 48-49
Class C IP addresses, 48-49
Class D IP addresses, 48-49
class declaration, 468
lease limit statement, 469
match if statement, 468
match statement, 468
spawn with statement, 468
class membership-based address allocation,
343-344
class-based address allocation, 344-346
classing clients, 340
explicit rules, 341
subclass-matching rules, 341-342
classless internet domain routing (CIDR), 49,
140
client FQDN option (host configuration parame-
ters), 132-133
client identifier option (DHCP), 62, 125-126
configuring (Microsoft DHCP client), 365
entering (Microsoft DHCP server), 453
client states
BOUND, 104-105
INIT, 104-112
INIT-REBOOT, 104-105
REBINDING, 105
RENEWING, 105
SELECTING, 104-105
client-state operator (numeric), 484
client/server transactions (DHCPv6)
client reconfiguration, 439
configuration without address assignment,
439
duplicate addresses, 439
initial address assignment, 438
IPv6 auto-configuration, 440
lease extensions, 439
BOOTP devices548
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obtaining additional addresses, 438
releasing addresses, 439
clients
allow known clients directive, 344
allow unknown clients directive, 344
Apple MacOS X DHCP
configuring, 374-378
controlling from command line, 376-378
availability of (DHCP benefits), 8
class groupings
user class option, 347-348
vendor class identifier option, 348-350
vendor-specific information option,
350-351
class-matching rules
explicit rule, 341
subclass-matching rule, 341-342
classing, 340
connectivity problems
debugging, 417-419
troubleshooting, 426
DHCP
dhcpcd, 365-366
DNS lease expirations, 184-185
DNS name selection, 180-183
FQDN option, 182
identification methods, 62
ISC, 367
name changes, 186
name collisions, 183-184
pump, 366
relocation of, 185-186
update configuration, 404-405
DHCP messages
broadcast flags from servers, 86
DHCPINFORM type, 93
DHCPRELEASE type, 94
DHCPREQUEST type, 92-93
forwarding to servers via relay agents,
86-88
retransmitting frequency, 90
server responses, 85-86
transaction IDs, 91-92
DHCP servers
configuration options, 217
IP address configuration, 256-257
DHCP services
alias configuration, 387
lease length versus number of clients,
328-329
relay agents, 61
DNS updates, 198
dropped packets to servers, troubleshooting,
420
dynamic address allocation
mixing with static allocation, 281-282
moving to static address allocation,
282-284
host declarations, 339
identification methods, 275
collision avoidance, 280
dhcp-client-identifier option, 276-279
link-layer address implementation,
276-277
non-standard options, 279
identifiers
potential problems with dual-boot client
systems, 427
uniqueness of, 426
inability to receive responses from servers,
troubleshooting, 420-422
incorrect option values on leases, trou-
bleshooting, 426
IP address leases
expiration of, 115
extending, 112-115
clients 549
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extending via broadcasts, 118
moving to new network, 115-116
renewal times, 114
terminating, 120
IP addresses
broadcast messages (DHCP), 84
failure to reserve, 428
initial configuration, obtaining, 105-109,
117-119
initial configuration, updating, 120
restart confirmations, 109-112, 118
unicast messages (DHCP), 85
use denial, 197-198
ISC DHCP
-d switch (background), 367
-g switch (silent startup), 367
additional options requests, 368
configuring, 368-369
controlling (OMAPI interface), 372-374
debugging, 370-372
DHCPDISCOVER message, 356
DHCPREQUEST message, 356
installing, 367-368
IP addresses, BOUND state, 357
IP addresses, failure to obtain, 356-357
IP addresses, lease expirations, 358
IP addresses, lease maintenance, 357-358
IP addresses, multiple network interfaces,
358
IP addresses, obtaining, 355-356
network interface customizations, 369
network setup script customizations, 370
operational overview, 355
overriding options sent by DHCP server,
368
unacceptable offers, rejecting, 368
update configuration, 404-405
ISC DHCP server
differentiating, 338-342
option spaces, 237-238
parameters, 235-238
scope settings, 240-243
specific scope settings, 243
user-defined options, 236-237
leases, locating (Microsoft DHCP server), 455
messages
DHCPDECLINE, 199
DHCPINFORM, 199
DHCPLEASEQUERY, 200
DHCPRELEASE, 199
Microsoft DHCP
client identifier option, 365
DHCPINFORM message, 365
emulation, 369-370
enabling, 359-362
host-name option, 363-365
installing, 359-362
Microsoft Web site resources, 359
user interface configuration (winipcfg),
362-363
server access, controlling based on client
identification, 286-288
static address allocation
assigning, 280-281
mixing with dynamic allocation, 281-282
update capabilities, DNS server configuration,
405-407
collisions
DHCP messages, avoiding, 91
multiple client identifiers, 276-277
avoiding, 280
colon hexadecimal notation (IPv6), 432
command-line arguments
-d switch, 245
-f switch, 245
clients550
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-lf switch, 246
-p switch, 245
-pf switch, 246
-play switch, 246
-q switch, 246
-t switch, 246
-tf switch, 246
ISC DHCP server, invoking, 244-246
commit event, ISC DHCP server leases, 352
COMMUNICATIONS-INTERRUPTED state, 168,
315
computers in role of DHCP servers
dynamic address probing, 27
explicit departure messages, 27
GSI management example, 21-27
IP address leases, 25-26
lease benefits, 27
moving to new network segment, 23-25
obtaining new IP addresses, 21-22
restarting, 22-23
retiring from service, 25
concat operator (data), 483
Concurrent Versioning System (CVS), DHCP con-
figurations, 309
conditional statements
clients, differentiating on ISC DHCP server,
338-340
else clause, 338
nesting, 339
config-option operator (data), 482
configure command, ISC DHCP server distribu-
tions, 227
configuring
Apple MacOS X DHCP client, 374-378
BOOTP file on Microsoft DHCP server, 448
client options (DHCP servers), 217
DHCP client, update capabilities, 404-405
DHCP servers
DNS server address, 32-34
global subnet options, 39
local subnet masks, 32-34
router addresses, 32-34
small office environment, 381-391
subnet options, 38-39
update capabilities, 400-404
DNS security policies, 397-400
DNS server
client update capabilities, 405-407
update capabilities, 402
DNS update policies, 395-397
failovers on ISC DHCP server, 305-314
GSI Network, DHCP operations, 19-27
individual subnets, 254-255
initial failover server, 304-305
IP addresses manually on DHCP servers,
321-322
ISC DHCP client, 368-369
update capabilities, 404-405
ISC DHCP server
automatic startups, 247-249
basic function of, 234-235
client options, 235-238
distributions, 227
DNS updates, 239
failover servers, 239
IP address assignments, 244
network settings, 240
OMAPI protocol settings, 239
option spaces, 237-238
parameters, 235
scopes, 240-243
specific scopes, 243
updates, 249
user-defined options, 236-237
configuring 551
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LAN ports for DHCP service, 390-391
Microsoft DHCP client
client identifier option, 365
DHCPINFORM message, 365
host-name option, 363-365
user interface (winipcfg), 362-363
multiple IP subnets on network segments,
266-272
network devices
BOOTP, 7
DHCP servers, 321-322
pre-DHCP development, 3-7
when not to use DHCP, 14
new options (DHCP servers), 219-220
overlay networks, 266-269
IP address allocation, 266-267
pitfalls, 270-272
routing avoidance, 268-269
relay agents (Microsoft DHCP server), 450-451
scopes
DHCP servers, 205-214
Microsoft DHCP server, 446
options (DHCP servers), 215
servers
authoritative setting, 253-257
options (DHCP servers), 216
shared networks, 266-269
IP address allocation, 266-267
pitfalls, 270-272
routing avoidance, 268-269
superscopes on DHCP servers, 212-213
user class options (DHCP servers), 218
users, pre-DHCP development, 5
vendor-specific options (DHCP servers), 217
WAN ports for DHCP service, 390
CONFLICT-DONE state, failover protocol opera-
tional state, 172
CONNECT message, failover peers, 162
CONNECTACK message, failover peers, 162
connectivity, debugging process
local, 417-419
relay agents, 419
server overview, 419-423
CONTACT message, failover peers, 162
controlling
Apple Mac OS X DHCP client from command
line, 376-378
ISC DHCP client via OMAPI interface,
372-374
converting servers, static address allocation to
dynamic allocation, 284-285
cooperating partners relationship (failovers),
301-302
configuring, 309-314
contact ports, setting, 310
contact timeout, setting, 310
free address balance, setting, 311
load balance override, setting, 312
load balance split, setting, 312
maximum number of pending updates, 310
MCLT, setting, 311
partner addresses, setting, 310
server roles, setting, 309
coordinated universal time (UTC), 134
D
dangling A (address) records, 408
data link layer (TCP/IP), 44
address translation, 45-46
hubs, 45
link-layer addresses, 45
link-layer framing, 44
switches, 45
configuring552
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data operators
binary-to-ascii, 481
concat, 483
config-option, 482
encode-int, 483
hardware, 482
host-name-decl, 483
leased-address, 483
option, 482
packet, 482
pick, 481
reverse, 482
string, 483
substring, 481
suffix, 481
text, 483
databases, synchronization, failover protocol,
160-161
datagrams, 46
delivery of TCP/IP internet layer, 49-50
fragmentation, 436
ddns-domainname statement, 492
ddns-hostname statement, 492
ddns-rev-domainname statement, 492
ddns-ttl statement, 493
ddns-update-style statement, 402-404
ddns-updates statement, 492
debugging
connectivity problems
local, 417-419
relay agents, 419
server overview, 419-423
DNS updates, 410-411
ISC DHCP client, 370-372
leases
failure to acquire, 414-415
failure to renew, 414-415
incorrect DNS information from DHCP
server, 415
process overview, 413
determining what is problem, 415
discovery of problem, 413
solution to problem, 416
tools, 416
declarations
dhcp.conf file, 460-462
class declaration, 468-469
dhcp-client-identifier option statement,
465
failover peer declaration, 472-475
fixed-address declaration, 466
group declaration, 470
hardware declaration, 465
host declaration, 464-465
include directive, 471
key declaration, 471
option space declaration, 470-471
pool declaration, 466-467
range declaration, 464
shared-network declaration, 463
subclass declaration, 469
subnet declaration, 463
zone declaration, 472
subnets, 254-255
default gateways, DHCP servers, 210-212
default IP time to live option (TCP/IP stack con-
figuration parameters), 136
default lease length, 35
default routers, TCP/IP internet layer, 49-50
default-lease-time statement, 487
defined operator (Boolean), 480
Delayed Authentication Protocol
DHCP message authentication, 97-99
IP addresses
confirming, 100
lease extensions, 101
obtaining, 99-100
Delayed Authentication Protocol 553
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delete operator (DNS), 485
delivering DHCP messages
collision avoidance, 91
reliability, 90-91
denial of service attacks, DHCPDECLINE mes-
sage, 199
desired lease time (failover protocol), 165
devices
mobility of, 8
moving to different network segments (pre-
DHCP development), 5
networks
configuring prior to DHCP, 3-7
configuring with BOOTP, 7
when not to use DHCP, 14
DHCFORCERENEW message, IP addresses, con-
figuration updates, 120
DHCINFORM message, IP addresses, obtaining
through non-DHCP protocol, 119
DHCP (Dynamic Host Configuration Protocol), 3,
59
benefits, 7
availability of clients, 8
device mobility, 8
large network implementation, 8
small network implementation, 9
centralized administration features, 66
client/server architecture, 66-67
clients
DNS dynamic updates, 180-187
DNS lease expirations, 184-185
DNS name selection, 180-183
DNS record authentication, 183
FQDN option, 182
common misconceptions
excess broadcast traffic, 11-12
reliability, 13-14
server load concerns, 12-13
DNS, domain name management, 178-179
goals
administrative control, 59-60
automated configuration services, 61
automatic DNS updates, 63
client identification, 62
correctness, 59-60
interserver communication, 62
minimal configuration changes, 61
reliability, 59-60
server-initiated message proposal, 63
GSI Network, operational example, 19-27
IP addresses
BOUND state, 357
dynamic assignment, 60
failure to obtain, 356-357
lease expirations, 358
lease maintenance, 357-358
multiple network interfaces, 358
obtaining, 355-356
name changes, 186
operational overview, 355
relocation of, 185-186
updates, configuring, 404-405
messages
authentication, 94-101
collision avoidance, 91
design constraints, 80-81
DHCPDISCOVER, 90, 97-98
DHCPFORCERENEW, 90, 94
DHCPINFORM, 93
DHCPKNOWN, 91
DHCPLEASEQUERY, 91, 94
DHCPRELEASE, 90, 94
DHCPREQUEST, 76-77, 92-93
DHCPUNKNOWN, 91
fixed-format section, 69-71
delete operator554
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message authentication code (MAC), 98
number option codes, 80-81
options section, 71-75
relay agents, 86-90
reliable delivery of, 90-91
special case considerations, 79-80
transaction IDs, 91-92
validation of, 99
variable-format section, 69-70
versus BOOTP messages, 69, 80-81
options
alphabetical listing, 507-515
numerical listing, 516-518
RFC 2132, 123-124
overview, 3
perceived problems
excess broadcast traffic, 11-12
reliability, 13-14
server load concerns, 12-13
rejected specification features
router configuration, 64
single IP address per interface, 63-64
relay agents, 61
RFC 2131 specification, 62
roots in BOOTP, 69
servers
authoritative name, 188-189
availability, 60
caching, 188-189
DNS dynamic updates, 182-183, 188-189
DNS name selection, 182-183
failover pairs, 314-318
merging configuration files, 305-309
primary, 188-189
secondary, 188-189
specific options
bootfile name, 130
client identifier, 125-126
DHCP message type, 124-125
end, 131
lease renewal time (T1), 127
lease renewal time (T2), 128
lease time, 127
maximum DHCP message size, 130
message, 129
option overload, 130
pad, 131
parameter request list, 129
requested IP address, 127
server identifier, 126
TFTP server name, 130
vendor class identifier, 128
vendor-specific information, 128-129
spurious traffic, handling, 13
when not to use, 14
DHCP client port (UDP port 68), 83-85
DHCP Manager
launching, 205
scopes
activating, 221
configuring, 210-212
creating, 207
default gateways, 210-212
lease durations, 210
naming, 208-209
superscopes
adding to existing scopes, 214
configuring, 212-213
window appearance, 443
DHCP message type option (DHCP-specific
options), 72-73, 124-125
DHCP message type option 555
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