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- Table of Contents
-
- H3C S9500 Operation Manual-Release2132[V2.03]-02 IP Services Volume
- 00-1Cover
- 01-ARP Configuration
- 02-DHCP Configuration
- 03-DNS Configuration
- 04-IP Addressing Configuration
- 05-IP Performance Configuration
- 06-UDP Helper Configuration
- 07-IPv6 Basics Configuration
- 08-Dual Stack Configuration
- 09-Tunneling Configuration
- 10-Adjacency Table Configuration
- Related Documents
-
| Title | Size | Download |
|---|---|---|
| 06-UDP Helper Configuration | 74.93 KB |
Table of Contents
Chapter 1 UDP Helper Configuration
1.1 Introduction to UDP Helper
1.3 Displaying and Maintaining UDP Helper
1.4 UDP Helper Configuration Examples
1.4.1 UDP Helper Configuration Example I
1.4.2 UDP Helper Configuration Example II
Chapter 1 UDP Helper Configuration
When configuring UDP Helper, go to these sections for information you are interested in:
l Displaying and Maintaining UDP Helper
l UDP Helper Configuration Examples
& Note:
UDP Helper can be currently configured on VLAN interfaces only.
1.1 Introduction to UDP Helper
Sometimes, a host needs to send broadcasts to obtain network configuration information or to request the names of other devices on the network. However, if the server or the device to be requested is located in another broadcast domain, the host cannot obtain such information through broadcast.
To solve this problem, the device provides the UDP Helper function to relay specified UDP broadcast packets. In other words, UDP Helper functions as a relay agent that converts UDP broadcast packets into unicast packets and forwards them to a specified destination server.
With UDP Helper enabled, the device decides whether to forward a received UDP broadcast packet according to the UDP destination port number of the packet.
l If the destination port number of the packet matches a port number pre-configured on the device, the device modifies the destination IP address in the IP header, and then sends the packet to the specified destination server.
l If not, the device sends the packet to the upper layer protocol for processing.
By default, with UDP Helper enabled, the device forwards broadcast packets with the six UDP destination port numbers listed in Table 1-1.
Table 1-1 List of default UDP ports
|
Protocol |
UDP port number |
|
Trivial file transfer protocol (TFTP) |
69 |
|
Domain name system (DNS) |
53 |
|
Time service |
37 |
|
NetBIOS name service (NetBIOS-NS) |
137 |
|
NetBIOS datagram service (NetBIOS-DS) |
138 |
|
Terminal access controller access control system (TACACS) |
49 |
1.2 Configuring UDP Helper
Follow these steps to configure UDP Helper:
|
To do… |
Use the command… |
Remarks |
|
Enter system view |
system-view |
— |
|
Enable UDP Helper |
udp-helper enable |
Required Disabled by default |
|
Enable the forwarding of packets with the specified UDP destination port number(s) |
udp-helper port { port-number | dns | netbios-ds | netbios-ns | tacacs | tftp | time } |
Required By default, the UDP helper enabled device forwards broadcast packets with any of the destination port numbers 69, 53, 37, 137, 138, and 49. |
|
Enter VLAN interface view |
interface vlan-interface-type interface-number |
— |
|
Configure the destination server to which UDP packets are to be forwarded |
udp-helper server ip-address |
Required By default, no destination server is configured. |
Caution:
l The UDP Helper enabled device cannot forward DHCP broadcast packets. That is to say, the UDP port number cannot be set to 67 or 68.
l The dns, netbios-ds, netbios-ns, tacacs, tftp, and time keywords correspond to the six default UDP port numbers. You can configure these default UDP port numbers by specifying port numbers or the corresponding parameters. For example, udp-helper port 53 and udp-helper port dns specify the same UDP port number.
l When you view the configuration information by using the display current-configuration command, the UDP Helper configuration of the default ports will not be displayed. UDP Helper configuration of these ports will be displayed only after UDP Helper is disabled.
l The configuration of all UDP ports (including the default ports) is removed if you disable UDP Helper.
l You can configure up to 256 UDP port numbers to enable the forwarding of packets with these UDP port numbers.
l You can configure up to 20 destination servers on an interface.
l If a destination server is configured on a VLAN interface, broadcast packets with the specified UDP destination port number that are received from a VLAN port will be unicast to that destination server after UDP Helper is enabled.
1.3 Displaying and Maintaining UDP Helper
|
To do… |
Use the command… |
Remarks |
|
Display the destination server information and the number of forwarded packets |
display udp-helper server [ interface interface-type interface-number ] |
Available in any view |
|
Clear statistics about packets forwarded |
reset udp-helper packet |
Available in user view |
1.4 UDP Helper Configuration Examples
1.4.1 UDP Helper Configuration Example I
I. Network requirements
On Switch A, configure UDP helper to forward broadcast packets (with UDP destination port number 55 and destination IP address 255.255.255.255 or 10.110.255.255 to the destination server at 10.2.1.1/16.
II. Network diagram
Figure 1-1 Network diagram for UDP Helper configuration I
III. Configuration procedure
& Note:
The following configuration assumes that a route from Switch A to the network segment 10.2.0.0/16 is available.
# Enable UDP Helper.
<SwitchA> system-view
[SwitchA] udp-helper enable
# Enable the forwarding of broadcast packets with UDP destination port 55.
[SwitchA] udp-helper port 55
# Specify the destination server 10.2.1.1 on VLAN-interface 1.
[SwitchA] interface vlan-interface 1
[SwitchA-Vlan-interface1] ip address 10.110.1.1 16
[SwitchA-Vlan-interface1] udp-helper server 10.2.1.1
1.4.2 UDP Helper Configuration Example II
I. Network requirements
On Switch C, configure UDP helper to forward broadcast packets (with UDP destination port number 55 and destination IP address 10.2.255.255 to the destination server 10.2.1.1/16.
II. Network diagram
Figure 1-2 Network diagram for UDP Helper configuration II
III. Configuration procedure
& Note:
The following configuration assumes that a route from Switch A to the network segment 10.2.0.0/16 is available.
1) Create VLANs. Add the interfaces to the corresponding VLANs, and configure IP addresses for the VLAN interfaces on Switch A, Switch B, and Switch C (omitted).
2) Configure Switch C
# Enable UDP Helper.
[SwitchC] udp-helper enable
# Enable the forwarding of broadcast packets with the UDP destination port 55.
[SwitchC] udp-helper port 55
# Specify the destination server 10.2.1.1 on VLAN-interface 2.
[SwitchC] interface vlan-interface 2
[SwitchC-Vlan-interface2] udp-helper server 10.2.1.1
