HP 6125G User manual
HP 6125 Blade Switch Series
Network Management and Monitoring
Configuration Guide
Part number: 5998-3162
Software version: Release 2103
Document version: 6W100-20120907
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Contents
Using ping, tracert, and system debugging··············································································································· 1
Ping·····················································································································································································1
Using a ping command to test network connectivity ····························································································1
Ping example ····························································································································································1
Tracert ················································································································································································3
Prerequisites ······························································································································································4
Using a tracert command to identify failed or all nodes in a path·····································································5
System debugging ····························································································································································5
Debugging information control switches················································································································5
Debugging a feature module ··································································································································6
Ping and tracert example ·················································································································································7
Configuring NTP ·························································································································································· 9
Overview············································································································································································9
NTP application························································································································································9
NTP advantages ·······················································································································································9
How NTP works························································································································································9
NTP message format ············································································································································· 10
Operation modes ·················································································································································· 12
NTP configuration task list············································································································································· 14
Configuring NTP operation modes ······························································································································ 14
Configuring the client/server mode ···················································································································· 15
Configuring the symmetric peers mode ·············································································································· 15
Configuring the broadcast mode························································································································· 16
Configuring the multicast mode ··························································································································· 17
Configuring optional parameters ································································································································· 17
Specifying the source interface for NTP messages ···························································································· 17
Disabling an interface from receiving NTP messages······················································································· 18
Configuring the allowed maximum number of dynamic sessions···································································· 18
Configuring the DSCP value for NTP messages································································································· 19
Configuring access-control rights ································································································································· 19
Configuration prerequisites ·································································································································· 20
Configuration procedure ······································································································································ 20
Configuring NTP authentication ··································································································································· 20
Configuring NTP authentication in client/server mode····················································································· 20
Displaying and maintaining NTP ································································································································· 21
NTP configuration examples········································································································································· 22
Configuring the client/server mode ···················································································································· 22
Configuring the NTP symmetric mode ················································································································ 23
Configuring NTP broadcast mode······················································································································· 25
Configuring NTP multicast mode ························································································································· 26
Configuring NTP client/server mode with authentication················································································· 28
Configuring NTP broadcast mode with authentication ····················································································· 30
Configuring the information center···························································································································34
Overview········································································································································································· 34
Classification of system information ···················································································································· 35
System information levels ····································································································································· 35
Output channels and destinations ······················································································································· 35
Outputting system information by source module······························································································ 36
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Default output rules of system information ·········································································································· 36
System information format···································································································································· 37
Information center configuration task list····················································································································· 40
Outputting system information to the console ············································································································· 40
Configuring a system information output rule for the console·········································································· 40
Enabling system information output to the console···························································································· 41
Outputting system information to the monitor terminal ······························································································ 41
Configuring a system information output rule for the monitor terminal ··························································· 41
Enabling system information output to the monitor terminal············································································· 42
Outputting system information to a log host ··············································································································· 42
Outputting system information to the trap buffer ········································································································ 43
Outputting system information to the log buffer·········································································································· 44
Outputting system information to the SNMP module ································································································· 44
Outputting system information to the Web interface·································································································· 45
Configuring synchronous information output ·············································································································· 46
Disabling an interface from generating link up/down logging information ··························································· 46
Displaying and maintaining information center ········································································································· 47
Information center configuration examples ················································································································· 47
Outputting log information to a UNIX log host ·································································································· 47
Outputting log information to a Linux log host··································································································· 49
Outputting log information to the console ·········································································································· 50
Configuring SNMP·····················································································································································52
Overview········································································································································································· 52
SNMP framework·················································································································································· 52
MIB and view-based MIB access control ············································································································ 52
SNMP operations ·················································································································································· 53
SNMP protocol versions ······································································································································· 53
SNMP configuration task list········································································································································· 53
Configuring SNMP basic parameters·························································································································· 53
Configuring SNMPv3 basic parameters············································································································· 53
Configuring SNMPv1 or SNMPv2c basic parameters······················································································ 55
Switching the NM-specific interface index format······································································································ 57
Configuration guidelines ······································································································································ 57
Configuration procedure ······································································································································ 57
Configuring SNMP logging ·········································································································································· 58
Configuring SNMP traps··············································································································································· 58
Enabling SNMP traps ··········································································································································· 58
Configuring the SNMP agent to send traps to a host ······················································································· 59
Displaying and maintaining SNMP ····························································································································· 60
SNMP configuration examples····································································································································· 61
SNMPv1/SNMPv2c configuration example ······································································································ 61
SNMPv3 configuration example·························································································································· 62
SNMP logging configuration example ··············································································································· 64
Configuring RMON ···················································································································································66
Overview········································································································································································· 66
Working mechanism············································································································································· 66
RMON groups ······················································································································································· 66
Configuring the RMON statistics function ··················································································································· 68
Configuring the RMON Ethernet statistics function···························································································· 68
Configuring the RMON history statistics function ······························································································ 68
Configuring the RMON alarm function ······················································································································· 69
Displaying and maintaining RMON ···························································································································· 70
Ethernet statistics group configuration example ········································································································· 71
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History group configuration example ·························································································································· 71
Alarm group configuration example···························································································································· 73
Configuring port mirroring ········································································································································76
Introduction to port mirroring········································································································································ 76
Terminologies of port mirroring ··························································································································· 76
Port mirroring classification and implementation······························································································· 77
Configuring local port mirroring ·································································································································· 79
Local port mirroring configuration task list ········································································································· 79
Creating a local mirroring group ························································································································ 79
Configuring source ports for the local mirroring group ···················································································· 79
Configuring the monitor port for the local mirroring group·············································································· 80
Configuring Layer 2 remote port mirroring ················································································································· 81
Layer 2 remote port mirroring configuration task list ························································································ 81
Configuring a remote source group (on the source device) ············································································· 81
Configuring a remote destination group (on the destination device) ······························································ 83
Displaying and maintaining port mirroring················································································································· 85
Port mirroring configuration examples························································································································· 85
Local port mirroring configuration example ······································································································· 85
Layer 2 remote port mirroring configuration example ······················································································ 87
Configuring traffic mirroring ·····································································································································90
Introduction to traffic mirroring····································································································································· 90
Traffic mirroring configuration task list ························································································································ 90
Configuring match criteria ············································································································································ 90
Configuring traffic mirroring of different types ··········································································································· 91
Mirroring traffic to a port ····································································································································· 91
Mirroring traffic to the CPU·································································································································· 91
Configuring a QoS policy············································································································································· 91
Applying a QoS policy ················································································································································· 92
Apply a QoS policy to a port ······························································································································ 92
Apply a QoS policy to a VLAN··························································································································· 92
Apply a QoS policy globally ······························································································································· 92
Displaying and maintaining traffic mirroring·············································································································· 93
Traffic mirroring configuration example ······················································································································ 93
Traffic mirroring configuration example ············································································································· 93
Configuring NQA ······················································································································································96
Overview········································································································································································· 96
NQA features ························································································································································ 96
NQA concepts······················································································································································· 98
NQA probe operation procedure ······················································································································· 99
NQA configuration task list ·········································································································································· 99
Configuring the NQA server ······································································································································100
Enabling the NQA client·············································································································································100
Creating an NQA test group······································································································································101
Configuring an NQA test group ································································································································101
Configuring ICMP echo tests······························································································································101
Configuring DHCP tests ······································································································································102
Configuring DNS tests ········································································································································103
Configuring FTP tests···········································································································································103
Configuring HTTP tests ········································································································································105
Configuring UDP jitter tests·································································································································105
Configuring SNMP tests ·····································································································································107
Configuring TCP tests··········································································································································108
Configuring UDP echo tests································································································································109
iv
Configuring voice tests ·······································································································································109
Configuring DLSw tests ·······································································································································111
Configuring the collaboration function ······················································································································112
Configuring threshold monitoring·······························································································································113
Configuration prerequisites ································································································································113
Configuration guidelines ····································································································································113
Configuration procedure ····································································································································113
Configuring the NQA statistics collection function···································································································115
Configuring the history records saving function ·······································································································115
Configuring optional parameters for an NQA test group·······················································································116
Configuring a schedule for an NQA test group·······································································································117
Configuration prerequisites ································································································································117
Configuration guidelines ····································································································································118
Configuration procedure ····································································································································118
Displaying and maintaining NQA·····························································································································118
NQA configuration examples ····································································································································119
ICMP echo test configuration example ·············································································································119
DHCP test configuration example······················································································································120
DNS test configuration example························································································································122
FTP test configuration example ··························································································································123
HTTP test configuration example························································································································124
UDP jitter test configuration example ················································································································125
SNMP test configuration example ·····················································································································128
TCP test configuration example ·························································································································129
UDP echo test configuration example ···············································································································130
Voice test configuration example ······················································································································132
DLSw test configuration example·······················································································································134
NQA collaboration configuration example······································································································135
Configuring sFlow··················································································································································· 138
sFlow configuration task list ········································································································································138
Configuring the sFlow agent and sFlow collector ····································································································139
Configuring flow sampling··········································································································································139
Configuring counter sampling ····································································································································140
Displaying and maintaining sFlow·····························································································································140
sFlow configuration example······································································································································140
Network requirements·········································································································································140
Troubleshooting sFlow configuration ·························································································································142
Configuring IPC······················································································································································· 143
Overview·······································································································································································143
Node·····································································································································································143
Link········································································································································································143
Channel ································································································································································143
Packet sending modes ········································································································································144
Enabling IPC performance statistics ···························································································································144
Displaying and maintaining IPC·································································································································145
Support and other resources ·································································································································· 146
Contacting HP ······························································································································································146
Subscription service ············································································································································146
Related information······················································································································································146
Documents····························································································································································146
Websites·······························································································································································146
Conventions ··································································································································································147
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Index ········································································································································································ 149
1
Using ping, tracert, and system debugging
Use the ping, tracert, and system debugging utilities to test network connectivity and identify network
problems.
Ping
The ping utility sends ICMP echo requests (ECHO-REQUEST) to the destination device. Upon receiving
the requests, the destination device responds with ICMP echo replies (ECHO-REPLY) to the source device.
The source device outputs statistics about the ping operation, including the number of packets sent,
number of echo replies received, and the round-trip time. You can measure the network performance by
analyzing these statistics.
Using a ping command to test network connectivity
Task Command
Remarks
Check whether a specified
address in an IP network is
reachable.
•For an IPv4 network:
ping [ ip ] [ -asource-ip | -c count | -f | -h
ttl | -iinterface-type interface-number | -m
interval | -n | -p pad | -q | -r | -s
packet-size | -t timeout | -tos tos | -v |
-vpn-instance vpn-instance-name ] * host
•For an IPv6 network:
ping ipv6 [ -a source-ipv6 | -c count | -m
interval | -s packet-size | -t timeout |-tos
tos ] * host [ -i interface-type
interface-number ]
Use one of the commands.
Available in any view.
IMPORTANT:
W
hen you configure the ping command for a low-speed network, HP recommends that you set a lar
g
er
v
alue for the timeout timer (indicated by the -t keyword in the command).
Ping example
Network requirements
Test the network connectivity between Device A and Device C in Figure 1. If they can reach each other,
get detailed information about routes from Device A to Device C.
2
Figure 1 Network diagram
Test procedure
# Use the ping command on Device A to test connectivity to Device C.
<DeviceA> ping 1.1.2.2
PING 1.1.2.2: 56 data bytes, press CTRL_C to break
Reply from 1.1.2.2: bytes=56 Sequence=1 ttl=254 time=205 ms
Reply from 1.1.2.2: bytes=56 Sequence=2 ttl=254 time=1 ms
Reply from 1.1.2.2: bytes=56 Sequence=3 ttl=254 time=1 ms
Reply from 1.1.2.2: bytes=56 Sequence=4 ttl=254 time=1 ms
Reply from 1.1.2.2: bytes=56 Sequence=5 ttl=254 time=1 ms
--- 1.1.2.2 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 1/41/205 ms
# Get detailed information about routes from Device A to Device C.
<DeviceA> ping -r 1.1.2.2
PING 1.1.2.2: 56 data bytes, press CTRL_C to break
Reply from 1.1.2.2: bytes=56 Sequence=1 ttl=254 time=53 ms
Record Route:
1.1.2.1
1.1.2.2
1.1.1.2
1.1.1.1
Reply from 1.1.2.2: bytes=56 Sequence=2 ttl=254 time=1 ms
Record Route:
1.1.2.1
1.1.2.2
1.1.1.2
1.1.1.1
Reply from 1.1.2.2: bytes=56 Sequence=3 ttl=254 time=1 ms
Record Route:
1.1.2.1
1.1.2.2
1.1.1.2
3
1.1.1.1
Reply from 1.1.2.2: bytes=56 Sequence=4 ttl=254 time=1 ms
Record Route:
1.1.2.1
1.1.2.2
1.1.1.2
1.1.1.1
Reply from 1.1.2.2: bytes=56 Sequence=5 ttl=254 time=1 ms
Record Route:
1.1.2.1
1.1.2.2
1.1.1.2
1.1.1.1
--- 1.1.2.2 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 1/11/53 ms
The test procedure with the ping –r command (see Figure 1) is as follows:
1. The source (Device A) sends an ICMP echo request with the RR option being empty to the
destination (Device C).
2. The intermediate device (Device B) adds the IP address of its outbound interface (1.1.2.1) to the RR
option of the ICMP echo request, and forwards the packet.
3. Upon receiving the request, the destination device copies the RR option in the request and adds the
IP address of its outbound interface (1.1.2.2) to the RR option. Then the destination device sends
an ICMP echo reply.
4. The intermediate device adds the IP address of its outbound interface (1.1.1.2) to the RR option in
the ICMP echo reply, and then forwards the reply.
5. Upon receiving the reply, the source device adds the IP address of its inbound interface (1.1.1.1)
to the RR option. Finally, you can get detailed information about routes from Device A to Device C:
1.1.1.1 <-> {1.1.1.2; 1.1.2.1} <-> 1.1.2.2.
Tracert
Tracert (also called "Traceroute") enables you to get the IP addresses of Layer 3 devices in the path to a
specific destination. You can use tracert to test network connectivity and identify failed nodes.
4
Figure 2 Network diagram
Tracert uses received ICMP error messages to get the IP addresses of devices. As shown in Figure 2,
tracert works as follows:
1. The source device (Device A) sends a UDP packet with a TTL value of 1 to the destination device
(Device D). The destination UDP port is not used by any application on the destination device.
2. The first hop (Device B, the first Layer 3 device that receives the packet) responds by sending a
TTL-expired ICMP error message to the source, with its IP address encapsulated. In this way, the
source device can get the address of the first Layer 3 device (1.1.1.2).
3. The source device sends a packet with a TTL value of 2 to the destination device.
4. The second hop (Device C) responds with a TTL-expired ICMP error message, which gives the
source device the address of the second Layer 3 device (1.1.2.2).
5. The process continues until the packet sent by the source device reaches the ultimate destination
device. Because no application uses the destination port specified in the packet, so the destination
device responds with a port-unreachable ICMP message to the source device, with its IP address
1.1.3.2 encapsulated. This way, the source device gets the IP address of the destination device
(1.1.3.2).
6. The source device thinks that the packet has reached the destination device after receiving the
port-unreachable ICMP message, and the path to the destination device is 1.1.1.2 to 1.1.2.2 to
1.1.3.2.
Prerequisites
Before you use a tracert command, perform the tasks in this section.
For an IPv4 network:
•Enable sending of ICMP timeout packets on the intermediate devices (the devices between the
source and destination devices). If the intermediate devices are HP devices, execute the ip
ttl-expires enable command on the devices. For more information about this command, see Layer
3—IP Services Command Reference.
•Enable sending of ICMP destination unreachable packets on the destination device. If the
destination device is an HP device, execute the ip unreachables enable command. For more
information about this command, see Layer 3—IP Services Command Reference.
•If there is an MPLS network between the source and destination devices and you need to display the
MPLS information during the tracert process, enable support for ICMP extensions on the source and
intermediate devices. If the source and intermediate devices are HP devices, execute the ip
5
icmp-extensions compliant command on the devices. For more information about this command,
see Layer 3—IP Services Command Reference.
For an IPv6 network:
•Enable sending of ICMPv6 timeout packets on the intermediate devices (the devices between the
source and destination devices). If the intermediate devices are HP devices, execute the ipv6
hoplimit-expires enable command on the devices. For more information about this command, see
Layer 3—IP Services Command Reference.
•Enable sending of ICMPv6 destination unreachable packets on the destination device. If the
destination device is an HP device, execute the ipv6 unreachables enable command. For more
information about this command, see Layer 3—IP Services Command Reference.
Using a tracert command to identify failed or all nodes in a
path
Task Command
Remarks
Display the routes from
source to destination.
•For an IPv4 network:
tracert [ -a source-ip | -f first-ttl |-m max-ttl |
-p port | -q packet-number | -tos tos |
-vpn-instance vpn-instance-name |-w
timeout ] * host
•For an IPv6 network:
tracert ipv6 [ -f first-ttl | -m max-ttl | -p port |
-q packet-number | -tos tos | -w timeout ] *
host
Use one of the commands.
Available in any view.
System debugging
The device supports various debugging for the majority of protocols and features and provides
debugging information to help users diagnose errors.
Debugging information control switches
The following two switches control the display of debugging information:
•Protocol debugging switch—Controls protocol-specific debugging information.
•Screen output switch—Controls whether to display the debugging information on a certain screen.
As shown in Figure 3, assume that the device can provide debugging for the three modules 1, 2, and 3.
The debugging information can be output on a terminal only when both the protocol debugging switch
and the screen output switch are turned on.
Output of debugging information depends on the configurations of the information center and the
debugging commands of each protocol and functional module. Debugging information is typically
displayed on a terminal (including console or VTY) for display. You can also send debugging
information to other destinations. For more information, see "Configuring the information center."
6
Figure 3 Relationship between the protocol and screen output switch
Debugging a feature module
Output of debugging commands is memory intensive. To guarantee system performance, enable
debugging only for modules that are in an exceptional condition. When debugging is complete, use the
undo debugging all command to disable all the debugging functions.
Configure the debugging,terminal debugging, and terminal monitor commands before you can display
detailed debugging information on the terminal. For more information about the terminal debugging
and terminal monitor commands, see Network Management and Monitoring Command Reference.
To debug a feature module and display the debugging information on a terminal:
Ste
p
Command
Remarks
1. Enable the terminal
monitoring of system
information.
terminal monitor
Optional.
The terminal monitoring on the
console is enabled by default and
the terminal monitoring on the
monitoring terminal is disabled by
default.
Available in user view.
2. Enable the terminal display of
debugging information. terminal debugging Disabled by default.
Available in user view.
3. Enable debugging for a
specified module.
debugging { all [ timeout time ] |
module-name [ option ] }
Disabled by default.
Available in user view.
4. Display the enabled
debugging functions.
display debugging [ interface
interface-type interface-number ]
[module-name ] [ | { begin |
exclude | include }
regular-expression ]
Optional.
Available in any view.
7
Ping and tracert example
Network requirements
As shown in Figure 4, Device A failed to Telnet Device C. Determine whether Device A and Device C can
reach each other. If they cannot reach each other, locate the failed nodes in the network.
Figure 4 Network diagram
Test procedure
1. Use the ping command to test connectivity between Device A and Device C.
<DeviceA> ping 1.1.2.2
PING 1.1.2.2: 56 data bytes, press CTRL_C to break
Request time out
Request time out
Request time out
Request time out
Request time out
--- 1.1.2.2 ping statistics ---
5 packet(s) transmitted
0 packet(s) received
100.00% packet loss
The output shows that Device A and Device C cannot reach each other.
2. Use the tracert command to identify failed nodes:
# Enable sending of ICMP timeout packets on Device B.
<DeviceB> system-view
[DeviceB] ip ttl-expires enable
# Enable sending of ICMP destination unreachable packets on Device C.
<DeviceC> system-view
[DeviceC] ip unreachables enable
# Execute the tracert command on Device A.
<DeviceA> tracert 1.1.2.2
traceroute to 1.1.2.2(1.1.2.2) 30 hops max,40 bytes packet, press CTRL_C to break
1 1.1.1.2 14 ms 10 ms 20 ms
2 * * *
3 * * *
4 * * *
5
<DeviceA>
The output shows that Device A and Device C cannot reach other, Device A and Device B can
reach each other, and an error has occurred on the connection between Device B and Device C.
8
3. Use the debugging ip icmp command on Device A and Device C to verify that they can send and
receive the specific ICMP packets, or use the display ip routing-table command to verify the
availability of active routes between Device A and Device C.
9
Configuring NTP
Overview
NTP is typically used in large networks to dynamically synchronize time among network devices. It
guarantees higher clock accuracy than manual system clock setting. In a small network that does not
require high clock accuracy, you can keep time synchronized among devices by changing their system
clocks one by one.
NTP runs over UDP and uses UDP port 123.
NTP application
An administrator is unable to keep time synchronized among all devices within a network by changing
the system clock on each station, because this is a huge work and does not guarantee clock precision.
NTP, however, allows quick clock synchronization within the entire network and ensures high clock
precision.
NTP is used when all devices within the network must keep consistent time. For example:
•In analyzing log and debugging information collected from different devices in network
management, time must be used as a reference basis.
•All devices must use the same reference clock in a charging system.
•To implement certain functions, such as a scheduled restart of all devices within the network, all
devices must keep consistent time.
•If multiple systems process a complex event in cooperation, these systems must use the same
reference clock to ensure the correct execution sequence.
•For incremental backup between a backup server and clients, timekeeping must be synchronized
between the backup server and all clients.
NTP advantages
•NTP uses a stratum to describe clock accuracy. The stratum ranges from 1 to 16. Clock accuracy
decreases as the stratum number increases. The stratum of a reference clock ranges from 1 to 15. A
stratum 16 clock is in unsynchronized state.
•The local clock of this Switch Series cannot operate as a reference clock. It can serve as an NTP
server only after it is synchronized.
•NTP supports access control and MD5 authentication.
•NTP can unicast, multicast, or broadcast protocol messages.
How NTP works
Figure 5 shows the basic workflow of NTP. Device A and Device B are connected over a network. They
have their own independent system clocks, which need to be automatically synchronized through NTP.
Assume that:
10
•Prior to system clock synchronization between Device A and Device B, the clock of Device A is set
to 10:00:00 am while that of Device B is set to 11:00:00 am.
•Device B is used as the NTP time server, so Device A synchronizes to Device B.
•It takes 1 second for an NTP message to travel from one device to the other.
Figure 5 Basic workflow of NTP
The synchronization process is as follows:
•Device A sends Device B an NTP message, which is timestamped when it leaves Device A. The
timestamp is 10:00:00 am (T1).
•When this NTP message arrives at Device B, it is timestamped by Device B. The timestamp is
11:00:01 am (T2).
•When the NTP message leaves Device B, Device B timestamps it. The timestamp is 11:00:02 am
(T3).
•When Device A receives the NTP message, the local time of Device A is 10:00:03 am (T4).
Up to now, Device A can calculate the following parameters based on the timestamps:
•The roundtrip delay of NTP message: Delay = (T4–T1) – (T3-T2) = 2 seconds.
•Time difference between Device A and Device B: Offset = ((T2-T1) + (T3-T4))/2 = 1 hour.
Based on these parameters, Device A can synchronize its own clock to the clock of Device B.
This is a rough description of how NTP works. For more information, see RFC 1305.
NTP message format
NTP uses two types of messages: clock synchronization and NTP control messages. All NTP messages
mentioned in this document refer to NTP clock synchronization messages. NTP control messages are
11
used in environments where network management is needed. Because NTP control messages are not
essential for clock synchronization, they are not described in this document.
A clock synchronization message is encapsulated in a UDP message in the format shown in Figure 6.
Figure 6 Clock synchronization message format
The main fields are described as follows:
•LI (Leap Indicator)—A 2-bit leap indicator. If set to 11, it warns of an alarm condition (clock
unsynchronized). If set to any other value, it is not to be processed by NTP.
•VN (Version Number)—A 3-bit version number that indicates the version of NTP. The latest version
is version 4.
•Mode—A 3-bit code that indicates the operation mode of NTP. This field can be set to these values:
{0—Reserved.
{1—Symmetric active.
{2—Symmetric passive.
{3—Client.
{4—Server.
{5—Broadcast or multicast.
{6—NTP control message.
{7—Reserved for private use.
•Stratum—An 8-bit integer that indicates the stratum level of the local clock, with the value ranging
from 1 to 16. Clock precision decreases from stratum 1 through stratum 16. A stratum 1 clock has
the highest precision, and a stratum 16 clock is not synchronized.
•Poll—An 8-bit signed integer that indicates the maximum interval between successive messages,
which is called the poll interval.
•Precision—An 8-bit signed integer that indicates the precision of the local clock.
12
•Root Delay—Roundtrip delay to the primary reference source.
•Root Dispersion—The maximum error of the local clock relative to the primary reference source.
•Reference Identifier—Identifier of the particular reference source.
•Reference Timestamp—The local time at which the local clock was last set or corrected.
•Originate Timestamp—The local time at which the request departed from the client for the service
host.
•Receive Timestamp—The local time at which the request arrived at the service host.
•Transmit Timestamp—The local time at which the reply departed from the service host for the client.
•Authenticator—Authentication information.
Operation modes
Devices that run NTP can implement clock synchronization in one of the following modes:
•Client/server mode
•Symmetric peers mode
•Broadcast mode
•Multicast mode
You can select operation modes of NTP as needed. If the IP address of the NTP server or peer is unknown
and many devices in the network need to be synchronized, adopt the broadcast or multicast mode. In the
client/server or symmetric peers mode, a device is synchronized from the specified server or peer, so
clock reliability is enhanced.
Client/server mode
Figure 7 Client/server mode
When operating in client/server mode, a client sends a clock synchronization message to servers with
the Mode field in the message set to 3 (client mode). Upon receiving the message, the servers
automatically operate in server mode and send a reply, with the Mode field in the messages set to 4
(server mode). Upon receiving the replies from the servers, the client performs clock filtering and selection
and synchronizes to the optimal reference source.
In client/server mode, a client can synchronize to a server, but a server cannot synchronize to a client.
Network
ServerClient
Clock
synchronization
message (Mode3)
Automatically works in
client/server mode and
sends a reply
Reply ( Mode4)
Performs clock filtering and
selection, and synchronizes its
local clock to that of the
optimal reference source
13
Symmetric peers mode
Figure 8 Symmetric peers mode
In symmetric peers mode, devices that operate in symmetric active mode and symmetric passive mode
exchange NTP messages with the Mode field 3 (client mode) and 4 (server mode). Then the device that
operates in symmetric active mode periodically sends clock synchronization messages, with the Mode
field in the messages set to 1 (symmetric active). The device that receives the messages automatically
enters symmetric passive mode and sends a reply, with the Mode field in the message set to 2 (symmetric
passive). This exchange of messages establishes symmetric peers mode between the two devices, so the
two devices can synchronize, or be synchronized by, each other. If the clocks of both devices have been
synchronized, the device whose local clock has a lower stratum level synchronizes the other device.
Broadcast mode
Figure 9 Broadcast mode
In broadcast mode, a server periodically sends clock synchronization messages to broadcast address
255.255.255.255, with the Mode field in the messages set to 5 (broadcast mode). Clients listen to the
broadcast messages from servers. When a client receives the first broadcast message, the client and the
server start to exchange messages with the Mode field set to 3 (client mode) and 4 (server mode), to
calculate the network delay between client and the server. Then, the client enters broadcast client mode.
The client continues listening to broadcast messages, and synchronizes its local clock based on the
received broadcast messages.
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