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Dell PowerConnect J-8216 Software Guide for JUNOS version 10.3 - Page 2621

Understanding DHCP Snooping for Port Security on J-EX Series Switches, DHCP Snooping Basics

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Chapter 93: Port Security Overview assigned, the attack will fail. See "Example: Configuring MAC Limiting to Protect the Switch from DHCP Starvation Attacks" on page 2583. Related • Understanding DHCP Snooping for Port Security on J-EX Series Switches on page 2549 Documentation • Understanding DAI for Port Security on J-EX Series Switches on page 2555 • Understanding MAC Limiting and MAC Move Limiting for Port Security on J-EX Series Switches on page 2557 • Understanding Trusted DHCP Servers for Port Security on J-EX Series Switches on page 2559 • Configuring Port Security (CLI Procedure) on page 2626 • Configuring Port Security (J-Web Procedure) on page 2627 Understanding DHCP Snooping for Port Security on J-EX Series Switches DHCP snooping allows the switch to monitor and control DHCP messages received from untrusted devices connected to the switch. When DHCP snooping is enabled, the system snoops the DHCP messages to view DHCP lease information and build and maintain a database of valid IP address to MAC address (IP-MAC) bindings called the DHCP snooping database. Only clients with valid bindings are allowed access to the network. • DHCP Snooping Basics on page 2549 • DHCP Snooping Process on page 2550 • DHCP Server Access on page 2551 • DHCP Snooping Table on page 2554 • Static IP Address Additions to the DHCP Snooping Database on page 2554 • Snooping DHCP Packets That Have Invalid IP Addresses on page 2554 DHCP Snooping Basics Dynamic Host Configuration Protocol (DHCP) allocates IP addresses dynamically, "leasing" addresses to devices so that the addresses can be reused when no longer needed. Hosts and end devices that require IP addresses obtained through DHCP must communicate with a DHCP server across the LAN. DHCP snooping acts as a guardian of network security by keeping track of valid IP addresses assigned to downstream network devices by a trusted DHCP server (the server is connected to a trusted network port). By default, all trunk ports on the switch are trusted and all access ports are untrusted for DHCP snooping. You can modify these defaults on each of the switch's interfaces. When DHCP snooping is enabled, the lease information from the switch (which is a DHCP client) is used to create the DHCP snooping database, a mapping of IP address to VLAN-MAC-address pairs. For each VLAN-MAC-address pair, the database stores the corresponding IP address. 2549

Section	Page
Table of Contents	7
About This Guide	69
How to Use This Guide	69
Downloading Software	70
Documentation Conventions	70
Repair and Warranty	71
Requesting Technical Support	71
Part 1: Junos OS for J-EX Series Switches Product Overview	73
Chapter 1: Software Overview	75
J-EX Series Switch Software Features Overview	75
Layer 3 Protocols Supported on J-EX Series Switches	85
Layer 3 Protocols Not Supported on J-EX Series Switches	86
Security Features for J-EX Series Switches Overview	88
High Availability Features for J-EX Series Switches Overview	90
VRRP	90
Graceful Protocol Restart	91
Redundant Routing Engines	91
Graceful Routing Engine Switchover	92
Virtual Chassis Software Upgrade and Failover Features	92
Link Aggregation	92
Understanding Software Infrastructure and Processes	94
Routing Engine and Packet Forwarding Engine	94
Junos OS Processes	95
Chapter 2: Supported Hardware	97
J-EX4200 Switches Hardware Overview	97
J-EX4200 Switches	97
Uplink Modules	98
Power over Ethernet (PoE) Ports	98
J-EX4200 Switch Models	98
J-EX8208 Switch Hardware Overview	99
Software	99
Chassis Physical Specifications	99
Routing Engines and Switch Fabric	100
Line Cards	101
Cooling System	101
Power Supplies	101
J-EX8216 Switch Hardware Overview	102
Software	102
Chassis Physical Specifications, LCD Panel, and Midplane	102
Routing Engines and Switch Fabric	104
Line Cards	105
Cooling System	105
Power Supplies	106
Part 2: Complete Software Configuration Statement Hierarchy	107
Chapter 3: Complete Software Configuration Statement Hierarchy	109
[edit access] Configuration Statement Hierarchy	109
[edit chassis] Configuration Statement Hierarchy	110
[edit class-of-service] Configuration Statement Hierarchy	110
[edit ethernet-switching-options] Configuration Statement Hierarchy	112
[edit firewall] Configuration Statement Hierarchy	114
[edit forwarding-options] Configuration Statement Hierarchy	115
[edit interfaces] Configuration Statement Hierarchy	116
[edit poe] Configuration Statement Hierarchy	120
[edit protocols] Configuration Statement Hierarchy	120
[edit routing-instances] Configuration Hierarchy	127
[edit snmp] Configuration Statement Hierarchy	127
[edit virtual-chassis] Configuration Statement Hierarchy	127
[edit vlans] Configuration Statement Hierarchy	128
Part 3: Software Installation	131
Chapter 4: Software Installation Overview	133
Installation Overview	133
Understanding Software Installation on J-EX Series Switches	133
Overview of the Software Installation Process	133
Software Package Security	134
Installing Software on a Virtual Chassis	134
Installing Software on J-EX8200 Switches with Redundant Routing Engines	134
Installing Software Using Automatic Software Download	135
Troubleshooting Software Installation	135
Junos OS Package Names	135
Understanding System Snapshot on J-EX Series Switches	136
Licenses Overview	137
Understanding Software Licenses for the J-EX Series Switch	137
Features Requiring a License	137
License Warning Messages	138
License Key Components for the J-EX Series Switch	138
Chapter 5: Installing Junos OS	141
Downloading Software Packages	141
Installing Software on a J-EX Series Switch with a Single Routing Engine (CLI Procedure)	142
Installing Software on a J-EX8200 Switch with Redundant Routing Engines (CLI Procedure)	143
Preparing the Switch for the Software Installation	144
Installing Software on the Backup Routing Engine	145
Installing Software on the Default Master Routing Engine	146
Returning Routing Control to the Default Master Routing Engine (Optional)	147
Installing Software on J-EX Series Switches (J-Web Procedure)	147
Installing Software Upgrades from a Server	148
Installing Software Upgrades by Uploading Files	149
Rebooting or Halting the J-EX Series Switch (J-Web Procedure)	149
Chapter 6: Booting the Switch, Upgrading Software, and Managing Licenses	151
Booting the Switch	151
Booting a J-EX Series Switch Using a Software Package Stored on a USB Flash Drive	151
Creating a Snapshot and Using It to Boot a J-EX Series Switch	152
Creating a Snapshot on a USB Flash Drive and Using It to Boot the Switch	152
Creating a Snapshot on an Internal Flash Drive and Using it to Boot the Switch	153
Upgrading Software	154
Upgrading Software Using Automatic Software Download on J-EX Series Switches	154
Managing Licenses	155
Managing Licenses for the J-EX Series Switch (CLI Procedure)	155
Adding New Licenses	155
Deleting Licenses	156
Saving License Keys	156
Managing Licenses for the J-EX Series Switch (J-Web Procedure)	156
Adding New Licenses	157
Deleting Licenses	157
Displaying License Keys	158
Downloading Licenses	158
Chapter 7: Verifying Software Installation	159
Routine Monitoring	159
Verifying That Automatic Software Download Is Working Correctly	159
Verifying That a System Snapshot Was Created on a J-EX Series Switch	160
Monitoring Licenses	160
Monitoring Licenses for the J-EX Series Switch	160
Displaying Installed Licenses and License Usage Details	161
Displaying Installed License Keys	162
Chapter 8: Troubleshooting Software Installation	163
Troubleshooting Software Installation	163
Recovering from a Failed Software Upgrade on a J-EX Series Switch	163
Rebooting from the Inactive Partition	164
Chapter 9: Configuration Statements for Software Installation	167
[edit chassis] Configuration Statement Hierarchy	167
auto-image-upgrade	168
Chapter 10: Operational Mode Commands for Software Installation	169
request system license add	170
request system license delete	171
request system license save	172
request system reboot	173
request system reboot	176
request system snapshot	178
request system software add	180
request system software delete	183
request system software rollback	185
request system software validate	187
show system autoinstallation status	189
show system boot-messages	190
show system license	191
show system snapshot	194
Part 4: User Interfaces	197
Chapter 11: User Interfaces Overview	199
User Interfaces—Overview	199
CLI User Interface Overview	199
CLI Overview	199
CLI Help and Command Completion	199
CLI Command Modes	200
J-Web User Interface for J-EX Series Switches Overview	201
Understanding J-Web Configuration Tools	203
Understanding J-Web User Interface Sessions	205
Chapter 12: Using the Configuration Tools	207
Using the CLI Terminal	207
Starting the J-Web Interface	208
Chapter 13: Operational Mode Commands for User Interfaces	209
set cli complete-on-space	210
set cli directory	211
set cli idle-timeout	212
set cli prompt	213
set cli restart-on-upgrade	214
set cli screen-length	215
set cli screen-width	216
set cli terminal	217
set cli timestamp	218
show cli	219
show cli authorization	221
show cli directory	224
show cli history	225
start shell	226
Part 5: Junos OS for J-EX Series Switches System Setup	227
Chapter 14: System Setup Overview	229
Junos OS—Overview	229
J-EX Series Switch Software Features Overview	229
Understanding Software Infrastructure and Processes	230
Routing Engine and Packet Forwarding Engine	230
Junos OS Processes	230
Chapter 15: Initial Configuration	233
Connecting and Configuring a J-EX Series Switch (CLI Procedure)	233
Connecting and Configuring a J-EX Series Switch (J-Web Procedure)	235
Configuring the LCD Panel on J-EX Series Switches (CLI Procedure)	238
Disabling or Enabling Menus and Menu Options on the LCD Panel	238
Configuring a Custom Display Message	239
Configuring Date and Time for the J-EX Series Switch (J-Web Procedure)	239
Configuring System Identity for a J-EX Series Switch (J-Web Procedure)	240
Chapter 16: Configuration Statements for System Setup	243
arp	243
authentication-key	244
auxiliary	245
boot-server (NTP)	245
broadcast	246
broadcast-client	247
console (Physical Port)	248
default-address-selection	249
domain-name (Router)	249
gre-path-mtu-discovery	250
host-name	250
icmpv4-rate-limit	251
icmpv6-rate-limit	252
inet6-backup-router	253
internet-options	254
ipip-path-mtu-discovery	255
ipv6-duplicate-addr-detection-transmits	255
ipv6-path-mtu-discovery	256
ipv6-path-mtu-discovery-timeout	256
ipv6-reject-zero-hop-limit	257
lcd-menu	258
location	259
menu-item	260
multicast-client	261
no-multicast-echo	262
no-ping-record-route	262
no-ping-time-stamp	263
no-redirects	263
no-tcp-rfc1323	264
no-tcp-rfc1323-paws	264
ntp	265
path-mtu-discovery	265
peer	266
ports	267
processes	268
server (NTP)	269
tcp-drop-synfin-set	269
traceoptions (SBC Configuration Process)	270
trusted-key	272
Chapter 17: Operational Mode Commands for System Setup	273
clear chassis display message	274
clear system reboot	276
configure	278
op	279
request chassis pic	281
request chassis routing-engine master	282
request system halt	284
request system logout	287
request system power-off	288
request system reboot	290
request system reboot	293
request system scripts convert	295
request system scripts refresh-from commit	296
request system scripts refresh-from event	297
request system scripts refresh-from op	298
request system storage cleanup	299
restart	301
set chassis display message	305
set date	307
show chassis firmware	308
show chassis lcd	310
show configuration	316
show host	319
show ntp associations	320
show ntp status	322
show system firmware	323
show system reboot	324
show system snapshot	326
show system software	328
show system storage	330
show system switchover	332
show system uptime	334
show system users	336
show system virtual-memory	338
show task replication	367
show version	368
Part 6: Junos OS for J-EX Series Switches Power Management	371
Chapter 18: Power Management Overview	373
Junos OS—Overview	373
J-EX Series Switch Software Features Overview	373
Power Management	374
Understanding Power Management on J-EX Series Switches	374
Power Priority of Line Cards	375
Power Supply Redundancy	376
Chapter 19: Initial Configuration	379
Configuring Power Supply Redundancy (CLI Procedure)	379
Configuring the Power Priority of Line Cards (CLI Procedure)	380
Chapter 20: Verifying Power Management	381
Verifying Power Configuration and Use	381
Chapter 21: Configuration Statements for Power Management	383
fpc	384
n-plus-n	385
power-budget-priority	385
psu	386
redundancy	386
Chapter 22: Operational Mode Commands for Power Management	387
show chassis power-budget-statistics	388
Part 7: Junos OS for J-EX Series Switches Configuration Management	391
Chapter 23: Configuration Management Overview	393
Configuration Files—Overview	393
Understanding Configuration Files for J-EX Series Switches	393
Configuration Files Terms	394
Understanding Automatic Refreshing of Scripts on J-EX Series Switches	395
Understanding Autoinstallation of Configuration Files on J-EX Series Switches	395
Typical Uses for Autoinstallation	395
Autoinstallation Configuration Files and IP Addresses	396
Typical Autoinstallation Process on a New Switch	396
J-EX Series Switches Default Configuration	397
J-EX4200 Default Configuration	397
J-EX8200 Switch Default Configuration	401
Chapter 24: Managing Junos OS Configuration	403
Using the Configuration Tools in J-Web	403
Using the CLI Viewer in the J-Web Interface to View Configuration Text	403
Using the CLI Editor in the J-Web Interface to Edit Configuration Text	403
Using the Point and Click CLI Tool in the J-Web Interface to Edit Configuration Text	404
Using the Commit Options to Commit Configuration Changes (J-Web Procedure)	406
Managing Junos OS Configuration	407
Uploading a Configuration File (CLI Procedure)	408
Uploading a Configuration File (J-Web Procedure)	409
Managing Configuration Files Through the Configuration History (J-Web Procedure)	410
Displaying Configuration History	410
Displaying Users Editing the Configuration	411
Comparing Configuration Files with the J-Web Interface	411
Downloading a Configuration File with the J-Web Interface	412
Loading a Previous Configuration File with the J-Web Interface	412
Loading a Previous Configuration File (CLI Procedure)	412
Reverting to the Default Factory Configuration for the J-EX Series Switch	413
Reverting to the Default Factory Configuration by Using the LCD Panel	414
Reverting to the Default Factory Configuration by Using the Load Factory Default Command	414
Reverting to the Rescue Configuration for the J-EX Series Switch	415
Setting or Deleting the Rescue Configuration (CLI Procedure)	416
Setting or Deleting the Rescue Configuration (J-Web Procedure)	417
Configuring Autoinstallation of Configuration Files (CLI Procedure)	417
Chapter 25: Verifying Configuration	421
Verifying Autoinstallation Status on a J-EX Series Switch	421
Chapter 26: Configuration Statements for Configuration Management	423
archival	423
archive-sites (Configuration File)	424
autoinstallation	425
commit synchronize	426
configuration	427
configuration-servers	428
interfaces	429
transfer-interval (Configuration)	430
transfer-on-commit	430
Chapter 27: Operational Mode Commands for Configuration Management	431
clear log	432
clear system commit	433
file archive	434
file checksum md5	436
file checksum sha1	437
file checksum sha-256	438
file compare	439
file copy	442
file delete	443
file list	444
file rename	445
file show	447
request system configuration rescue delete	448
request system configuration rescue save	449
request system scripts refresh-from commit	450
request system scripts refresh-from event	451
request system scripts refresh-from op	452
show system commit	453
show system configuration archival	455
show system configuration rescue	456
show system rollback	457
test configuration	459
Part 8: User and Access Management on J-EX Series Switches	461
Chapter 28: User and Access Management on J-EX Series Switches Overview	463
J-EX Series Switch Software Features Overview	463
Understanding Software Infrastructure and Processes	464
Routing Engine and Packet Forwarding Engine	464
Junos OS Processes	464
Chapter 29: User Access Management Configuration	467
Configuring Management Access for the J-EX Series Switch (J-Web Procedure)	467
Generating SSL Certificates to Be Used for Secure Web Access	470
Configuring MS-CHAPv2 to Provide Password-Change Support (CLI Procedure)	471
Chapter 30: Monitoring Users	473
Managing Users (J-Web Procedure)	473
Chapter 31: Troubleshooting User Access Management	477
Troubleshooting Loss of the Root Password	477
Chapter 32: Configuration Statements for User and Access Management	481
allow-commands	481
allow-configuration	482
announcement	482
authentication (Login)	483
authentication-order	484
change-type	485
class (Assigning a Class to an Individual User)	485
class (Defining Login Classes)	486
deny-commands	487
deny-configuration	488
format	489
full-name	489
idle-timeout	490
login	491
login-alarms	492
login-tip	492
maximum-length	493
message	493
minimum-changes	494
minimum-length	495
password (Login)	495
permissions	496
radius-options	496
retry-options	497
root-authentication	498
root-login	499
tacplus-options	500
tacplus-server	501
traceoptions (Address-Assignment Pool)	502
uid	503
user (Access)	504
Chapter 33: Operational Mode Commands for User and Access Management	505
request message	506
show subscribers	507
Part 9: Junos OS for J-EX Series Switches System Services	515
Chapter 34: System Services Overview	517
DHCP Overview	517
DHCP Services for J-EX Series Switches Overview	517
DHCP/BOOTP Relay for J-EX Series Switches Overview	518
Chapter 35: System Services Configuration	519
Configuring DHCP Services (J-Web Procedure)	519
Configuring a DHCP SIP Server (CLI Procedure)	522
Chapter 36: Monitoring System Services	523
Monitoring DHCP Services	523
Chapter 37: Configuration Statements for System Services	527
boot-file	527
boot-server (DHCP)	528
bootp	529
ca-name	530
cache-size	530
cache-timeout-negative	531
certificates	532
certification-authority	533
client-identifier	533
connection-limit	534
crl (Encryption Interface)	535
default-lease-time	535
description	536
dhcp	537
domain	538
domain-name (DHCP)	538
domain-search	539
encoding	539
enrollment-retry	540
enrollment-url	540
file	541
ftp	541
helpers	542
http	544
https	545
interface (BOOTP)	546
interface (DNS and TFTP Packet Forwarding or Relay Agent)	547
ldap-url	547
load-key-file	548
local	549
local-certificate	550
maximum-certificates	550
maximum-hop-count	551
maximum-lease-time	551
minimum-wait-time	552
name-server	552
no-listen	553
outbound-ssh	554
path-length	556
pool	557
port (HTTP/HTTPS)	558
port (SRC Server)	558
protocol-version	559
rate-limit	559
server (DHCP and BOOTP Relay Agent)	560
server (DNS and TFTP Service)	561
server-identifier	562
servers	563
service-deployment	563
services	564
session	566
sip-server	567
source-address (SRC Software)	567
source-address-giaddr	568
ssh	568
static-binding	569
telnet	570
tftp	570
traceoptions	571
traceoptions (DHCP Server)	573
traceoptions (DNS and TFTP Packet Forwarding)	576
web-management	578
wins-server	579
Chapter 38: Operational Mode Commands for System Services	581
clear system services dhcp binding	582
clear system services dhcp conflict	583
clear system services dhcp statistics	584
request ipsec switch	585
request security certificate (signed)	586
request security key-pair	587
request security certificate (unsigned)	588
show system services dhcp binding	589
show system services dhcp conflict	591
show system services dhcp global	592
show system services dhcp pool	594
show system services dhcp statistics	596
show system services service-deployment	598
ssh	599
telnet	601
Part 10: Junos OS for J-EX Series Switches System Monitoring	603
Chapter 39: System Monitoring Overview	605
Understanding Alarm Types and Severity Levels on J-EX Series Switches	605
Dashboard for J-EX Series Switches	606
System Information Panel	607
Health Status Panel	607
Capacity Utilization Panel	608
Alarms Panel	608
Chassis Viewer	609
Chapter 40: Administering and Monitoring System Functions	613
Monitoring System Log Messages	613
Checking Active Alarms with the J-Web Interface	616
Monitoring Chassis Alarms for a J-EX8200 Switch	617
Monitoring Switch Control Traffic	620

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2,423
2,424
2,425
2,426
2,427
2,428
2,429
2,430
2,431
2,432
2,433
2,434
2,435
2,436
2,437
2,438
2,439
2,440
2,441
2,442
2,443
2,444
2,445
2,446
2,447
2,448
2,449
2,450
2,451
2,452
2,453
2,454
2,455
2,456
2,457
2,458
2,459
2,460
2,461
2,462
2,463
2,464
2,465
2,466
2,467
2,468
2,469
2,470
2,471
2,472
2,473
2,474
2,475
2,476
2,477
2,478
2,479
2,480
2,481
2,482
2,483
2,484
2,485
2,486
2,487
2,488
2,489
2,490
2,491
2,492
2,493
2,494
2,495
2,496
2,497
2,498
2,499
2,500
2,501
2,502
2,503
2,504
2,505
2,506
2,507
2,508
2,509
2,510
2,511
2,512
2,513
2,514
2,515
2,516
2,517
2,518
2,519
2,520
2,521
2,522
2,523
2,524
2,525
2,526
2,527
2,528
2,529
2,530
2,531
2,532
2,533
2,534
2,535
2,536
2,537
2,538
2,539
2,540
2,541
2,542
2,543
2,544
2,545
2,546
2,547
2,548
2,549
2,550
2,551
2,552
2,553
2,554
2,555
2,556
2,557
2,558
2,559
2,560
2,561
2,562
2,563
2,564
2,565
2,566
2,567
2,568
2,569
2,570
2,571
2,572
2,573
2,574
2,575
2,576
2,577
2,578
2,579
2,580
2,581
2,582
2,583
2,584
2,585
2,586
2,587
2,588
2,589
2,590
2,591
2,592
2,593
2,594
2,595
2,596
2,597
2,598
2,599
2,600
2,601
2,602
2,603
2,604
2,605
2,606
2,607
2,608
2,609
2,610
2,611
2,612
2,613
2,614
2,615
2,616
2,617
2,618
2,619
2,620
2,621
2,622
2,623
2,624
2,625
2,626
2,627
2,628
2,629
2,630
2,631
2,632
2,633
2,634
2,635
2,636
2,637
2,638
2,639
2,640
2,641
2,642
2,643
2,644
2,645
2,646
2,647
2,648
2,649
2,650
2,651
2,652
2,653
2,654
2,655
2,656
2,657
2,658
2,659
2,660
2,661
2,662
2,663
2,664
2,665
2,666
2,667
2,668
2,669
2,670
2,671
2,672
2,673
2,674
2,675
2,676
2,677
2,678
2,679
2,680
2,681
2,682
2,683
2,684
2,685
2,686
2,687
2,688
2,689
2,690
2,691
2,692
2,693
2,694
2,695
2,696
2,697
2,698
2,699
2,700
2,701
2,702
2,703
2,704
2,705
2,706
2,707
2,708
2,709
2,710
2,711
2,712
2,713
2,714
2,715
2,716
2,717
2,718
2,719
2,720
2,721
2,722
2,723
2,724
2,725
2,726
2,727
2,728
2,729
2,730
2,731
2,732
2,733
2,734
2,735
2,736
2,737
2,738
2,739
2,740
2,741
2,742
2,743
2,744
2,745
2,746
2,747
2,748
2,749
2,750
2,751
2,752
2,753
2,754
2,755
2,756
2,757
2,758
2,759
2,760
2,761
2,762
2,763
2,764
2,765
2,766
2,767
2,768
2,769
2,770
2,771
2,772
2,773
2,774
2,775
2,776
2,777
2,778
2,779
2,780
2,781
2,782
2,783
2,784
2,785
2,786
2,787
2,788
2,789
2,790
2,791
2,792
2,793
2,794
2,795
2,796
2,797
2,798
2,799
2,800
2,801
2,802
2,803
2,804
2,805
2,806
2,807
2,808
2,809
2,810
2,811
2,812
2,813
2,814
2,815
2,816
2,817
2,818
2,819
2,820
2,821
2,822
2,823
2,824
2,825
2,826
2,827
2,828
2,829
2,830
2,831
2,832
2,833
2,834
2,835
2,836
2,837
2,838
2,839
2,840
2,841
2,842
2,843
2,844
2,845
2,846
2,847
2,848
2,849
2,850
2,851
2,852
2,853
2,854
2,855
2,856
2,857
2,858
2,859
2,860
2,861
2,862
2,863
2,864
2,865
2,866
2,867
2,868
2,869
2,870
2,871
2,872
2,873
2,874
2,875
2,876
2,877
2,878
2,879
2,880
2,881
2,882
2,883
2,884
2,885
2,886
2,887
2,888
2,889
2,890
2,891
2,892
2,893
2,894
2,895
2,896
2,897
2,898
2,899
2,900
2,901
2,902
2,903
2,904
2,905
2,906
2,907
2,908
2,909
2,910
2,911
2,912
2,913
2,914
2,915
2,916
2,917
2,918
2,919
2,920
2,921
2,922
2,923
2,924
2,925
2,926
2,927
2,928
2,929
2,930
2,931
2,932
2,933
2,934
2,935
2,936
2,937
2,938
2,939
2,940
2,941
2,942
2,943
2,944
2,945
2,946
2,947
2,948
2,949
2,950
2,951
2,952
2,953
2,954
2,955
2,956
2,957
2,958
2,959
2,960
2,961
2,962
2,963
2,964
2,965
2,966
2,967
2,968
2,969
2,970
2,971
2,972
2,973
2,974
2,975
2,976
2,977
2,978
2,979
2,980
2,981
2,982
2,983
2,984
2,985
2,986
2,987
2,988
2,989
2,990
2,991
2,992
2,993
2,994
2,995
2,996
2,997
2,998
2,999
3,000
3,001
3,002
3,003
3,004
3,005
3,006
3,007
3,008
3,009
3,010
3,011
3,012
3,013
3,014
3,015
3,016
3,017
3,018
3,019
3,020
3,021
3,022
3,023
3,024
3,025
3,026
3,027
3,028
3,029
3,030
3,031
3,032
3,033
3,034
3,035
3,036
3,037
3,038
3,039
3,040
3,041
3,042
3,043
3,044
3,045
3,046
3,047
3,048
3,049
3,050
3,051
3,052
3,053
3,054
3,055
3,056
3,057
3,058
3,059
3,060
3,061
3,062
3,063
3,064
3,065
3,066
3,067
3,068
3,069
3,070
3,071
3,072
3,073
3,074
3,075
3,076
3,077
3,078
3,079
3,080
3,081
3,082
3,083
3,084
3,085
3,086
3,087
3,088
3,089
3,090
3,091
3,092
3,093
3,094
3,095
3,096
3,097
3,098
3,099
3,100
3,101
3,102
3,103
3,104
3,105
3,106
3,107
3,108
3,109
3,110
3,111
3,112
3,113
3,114
3,115
3,116
3,117
3,118
3,119
3,120
3,121
3,122
3,123
3,124
3,125
3,126
3,127
3,128
3,129
3,130
3,131
3,132
3,133
3,134
3,135
3,136
3,137
3,138
3,139
3,140
3,141
3,142
3,143
3,144
3,145
3,146
3,147
3,148
3,149
3,150
3,151
3,152
3,153
3,154
3,155
3,156
3,157
3,158
3,159
3,160
3,161
3,162
3,163
3,164
3,165
3,166
3,167
3,168
3,169
3,170
3,171
3,172
3,173
3,174
3,175
3,176
3,177
3,178
3,179
3,180
3,181
3,182
3,183
3,184
3,185
3,186
3,187
3,188
3,189
3,190
3,191
3,192
3,193
3,194
3,195
3,196
3,197
3,198
3,199
3,200
3,201
3,202
3,203
3,204
3,205
3,206
3,207
3,208
3,209
3,210
3,211
3,212
3,213
3,214
3,215
3,216
3,217
3,218
3,219
3,220
3,221
3,222
3,223
3,224
3,225
3,226
3,227
3,228
3,229
3,230
3,231
3,232
3,233
3,234
3,235
3,236
3,237
3,238
3,239
3,240
3,241
3,242
3,243
3,244
3,245
3,246
3,247
3,248
3,249
3,250
3,251
3,252
3,253
3,254
3,255
3,256
3,257
3,258
3,259
3,260
3,261
3,262
3,263
3,264
3,265
3,266
3,267
3,268
3,269
3,270
3,271
3,272
3,273
3,274
3,275
3,276
3,277
3,278
3,279
3,280
3,281
3,282
3,283
3,284
3,285
3,286
3,287
3,288
3,289
3,290
3,291
3,292
3,293
3,294
3,295
3,296
3,297
3,298
3,299
3,300
3,301
3,302
3,303
3,304
3,305
3,306
3,307
3,308
3,309
3,310
3,311
3,312
3,313
3,314
3,315
3,316
3,317
3,318
3,319
3,320
3,321
3,322
3,323
3,324
3,325
3,326
3,327
3,328
3,329
3,330
3,331
3,332
3,333
3,334
3,335
3,336
3,337
3,338
3,339
3,340
3,341
3,342
3,343
3,344
3,345
3,346
3,347
3,348
3,349
3,350
3,351
3,352
3,353
3,354
3,355
3,356
3,357
3,358
3,359
3,360
3,361
3,362
3,363
3,364
3,365
3,366
3,367
3,368
3,369
3,370
3,371
3,372
3,373
3,374
3,375
3,376
3,377
3,378
3,379
3,380
3,381
3,382
3,383
3,384
3,385
3,386
3,387
3,388
3,389
3,390
3,391
3,392
3,393
3,394
3,395
3,396
3,397
3,398
3,399
3,400
3,401
3,402
3,403
3,404
3,405
3,406
3,407
3,408
3,409
3,410
3,411
3,412
3,413
3,414
3,415
3,416
3,417
3,418
3,419
3,420
3,421
3,422
3,423
3,424
3,425
3,426
3,427
3,428
3,429
3,430
3,431
3,432
3,433
3,434
3,435
3,436
3,437
3,438
3,439
3,440
3,441
3,442
3,443
3,444
3,445
3,446
3,447
3,448
3,449
3,450
3,451
3,452
3,453
3,454
3,455
3,456
3,457
3,458
3,459
3,460
3,461
3,462
3,463
3,464
3,465
3,466
3,467
3,468
3,469
3,470
3,471
3,472
3,473
3,474
3,475
3,476
3,477
3,478
3,479
3,480
3,481
3,482
3,483
3,484
3,485
3,486
3,487
3,488
3,489
3,490
3,491
3,492
3,493
3,494
3,495
3,496
3,497
3,498
3,499
3,500
3,501
3,502
3,503
3,504
3,505
3,506
3,507
3,508
3,509
3,510
3,511
3,512
3,513
3,514
3,515
3,516
3,517
3,518
3,519
3,520
3,521
3,522
3,523
3,524
3,525
3,526
3,527
3,528
3,529
3,530
3,531
3,532
3,533
3,534
3,535
3,536
3,537
3,538
3,539
3,540
3,541
3,542
3,543
3,544
3,545
3,546
3,547
3,548
3,549
3,550
3,551
3,552
3,553
3,554
3,555
3,556
3,557
3,558
3,559
3,560
3,561
3,562
3,563
3,564
3,565
3,566
3,567
3,568
3,569
3,570
3,571
3,572
3,573
3,574
3,575
3,576
3,577
3,578
3,579
3,580
3,581
3,582
3,583
3,584
3,585
3,586
3,587
3,588
3,589
3,590
3,591
3,592
3,593
3,594
3,595
3,596
3,597
3,598
3,599
3,600
3,601
3,602
3,603
3,604
3,605
3,606
3,607
3,608
3,609
3,610
3,611
3,612
3,613
3,614
3,615
3,616
3,617
3,618
3,619
3,620
3,621
3,622
3,623
3,624
3,625
3,626
3,627
3,628
3,629
3,630
3,631
3,632
3,633
3,634
3,635
3,636
3,637
3,638
3,639
3,640
3,641
3,642
3,643
3,644
3,645
3,646
3,647
3,648
3,649
3,650
3,651
3,652
3,653
3,654
3,655
3,656
3,657
3,658
3,659
3,660

Match case Limit results 1 per page

assigned, the attack will fail. See “Example: Configuring MAC Limiting to Protect the

Switch from DHCP Starvation Attacks” on page 2583.

Documentation

Understanding DHCP Snooping for Port Security on J-EX Series Switches on page 2549

•

Understanding DAI for Port Security on J-EX Series Switches on page 2555

•

Understanding MAC Limiting and MAC Move Limiting for Port Security on J-EX Series

Switches on page 2557

•

Understanding Trusted DHCP Servers for Port Security on J-EX Series Switches on

page 2559

•

Configuring Port Security (CLI Procedure) on page 2626

•

Configuring Port Security (J-Web Procedure) on page 2627

Understanding DHCP Snooping for Port Security on J-EX Series Switches

DHCP snooping allows the switch to monitor and control DHCP messages received from

untrusted devices connected to the switch. When DHCP snooping is enabled, the system

snoops the DHCP messages to view DHCP lease information and build and maintain a

database of valid IP address to MAC address (IP-MAC) bindings called the DHCP snooping

database. Only clients with valid bindings are allowed access to the network.

•

DHCP Snooping Basics on page 2549

•

DHCP Snooping Process on page 2550

•

DHCP Server Access on page 2551

•

DHCP Snooping Table on page 2554

•

Static IP Address Additions to the DHCP Snooping Database on page 2554

•

Snooping DHCP Packets That Have Invalid IP Addresses on page 2554

DHCP Snooping Basics

Dynamic Host Configuration Protocol (DHCP) allocates IP addresses dynamically,

“leasing” addresses to devices so that the addresses can be reused when no longer

needed. Hosts and end devices that require IP addresses obtained through DHCP must

communicate with a DHCP server across the LAN.

DHCP snooping acts as a guardian of network security by keeping track of valid IP

addresses assigned to downstream network devices by a trusted DHCP server (the server

is connected to a trusted network port). By default, all trunk ports on the switch are

trusted and all access ports are untrusted for DHCP snooping. You can modify these

defaults on each of the switch's interfaces.

When DHCP snooping is enabled, the lease information from the switch (which is a DHCP

client) is used to create the DHCP snooping database, a mapping of IP address to

VLAN–MAC-address pairs. For each VLAN–MAC-address pair, the database stores the

corresponding IP address.

2549

Chapter 93: Port Security Overview