HP 5500 Ei 5500 Si Switch Series Configuration Guide
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system-view
[Sysname] ip host host.com 10.1.1.2
# Use the ping host.com command to verify that the device can use static domain name resolution to
resolve domain name host.com into IP address 10.1.1.2.
[Sysname] ping host.com
PING host.com (10.1.1.2):
56 data bytes, press CTRL_C to break
Reply from 10.1.1.2: bytes=56 Sequence=1 ttl=128 time=1 ms
Reply from 10.1.1.2: bytes=56 Sequence=2 ttl=128 time=4 ms
Reply from 10.1.1.2: bytes=56 Sequence=3 ttl=128 time=3 ms
Reply...](http://img.usermanuals.tech/thumb/36/58909/w64_hp-5500-ei-5500-si-switch-series-configuration-guide-573.png "Page 574
92
system-view
[Sysname] ip host host.com 10.1.1.2
# Use the ping host.com command to verify that the device can use static domain name resolution to
resolve domain name host.com into IP address 10.1.1.2.
[Sysname] ping host.com
PING host.com (10.1.1.2):
56 data bytes, press CTRL_C to break
Reply from 10.1.1.2: bytes=56 Sequence=1 ttl=128 time=1 ms
Reply from 10.1.1.2: bytes=56 Sequence=2 ttl=128 time=4 ms
Reply from 10.1.1.2: bytes=56 Sequence=3 ttl=128 time=3 ms
Reply...")
89 Configuration restrictions and guidelines • You can configure up to six DNS servers, including those with IPv6 addresses, in system view, and up to six DNS servers on all interfaces of a device. • A DNS server configured in system view has a higher priority than one configured in interface view. A DNS server configured earlier has a higher priority than one configured later in the same view. A DNS server manually configured has a higher priority than one dynamically obtained through DHCP. A name query request is first sent to the DNS server that has the highest priority. If no reply is received, it is sent to the DNS server that has the second highest priority, and thus in turn. • You can specify up to ten DNS suffixes. Configuration procedure To configure dynamic domain name resolution: Step Command Remarks 1. Enter system view. system-view N/A 2. Enable dynamic domain name resolution. dns resolve Disabled by default. 3. Specify a DNS server. • (Approach 1) In System view: dns server ip-address • (Approach 2) In interface view: a. interface interface-type interface-number b. dns server ip-address c. quit Use either approach. Not specified by default. 4. Configure a DNS suffix. dns domain domain-name Optional. Not configured by default. Only the provided domain name is resolved. Configuring the DNS proxy You can specify multiple DNS servers by using the dns server command repeatedly. Upon receiving a name query request from a client, the DNS proxy forwards the request to the DNS server that has the highest priority. If having not received a reply, it forwards the request to a DNS server that has the second highest priority, and thus in turn. To configure the DNS proxy: Step Command Remarks 1. Enter system view. system-view N/A 2. Enable DNS proxy. dns proxy enable Disabled by default.
90 Step Command Remarks 3. Specify a DNS server. • (Approach 1) In system view: dns server ip-address • (Approach 2) In interface view: a. interface interface-type interface-number b. dns server ip-address Use either approach. No DNS server is specified by default. Configuring DNS spoofing DNS spoofing is effective only when: • The DNS proxy is enabled on the device. • No DNS server or route to any DNS server is specified on the device. To configure DNS spoofing: Step Command Remarks 1. Enter system view. system-view N/A 2. Enable DNS spoofing and specify the translated IP address. dns spoofing ip-address Disabled by default Setting the DSCP value for DNS packets Step Command Remarks 1. Enter system view. system-view N/A 2. Set the DSCP value for DNS packets. dns dscp dscp-value Optional. By default, the DSCP value for DNS packets is 0. Specifying the source interface for DNS packets By default, the device uses the primary IP address of the output interface of the matching route as the source IP address of a DNS request. Therefore, the source IP address of the DNS packets may vary with DNS servers. In some scenarios, the DNS server only responds to DNS requests sourced from a specific IP address. In such cases, you must specify the source interface for the DNS packets so that the device can always use the primary IP address of the specified source interface as the source IP address of DNS packets. To specify the source interface for DNS packets: Step Command Remarks 1. Enter system view. system-view N/A
91
Step Command Remarks
2. Set the DSCP value for DNS
packets. dns source-interface
interface-type interface-number By default, no source interface for
DNS packets is specified. The
device uses the primary IP
address of the output interface of
the matching route as the source
IP address of a DNS request.
Displaying and maintaining IPv4 DNS
Task Command Remarks
Display the static IPv4 domain
name resolution table.
display ip host [ |
{ begin | exclude |
include } regular-expression ] Available in any view
Display IPv4 DNS server
information. display dns server [ dynamic
] [ | { begin |
exclude | include } regular-expression ] Available in any view
Display DNS suffixes. display dns domain
[ dynamic ] [ | { begin |
exclude | include } regular-expression ] Available in any view
Display the information of the
dynamic IPv4 domain name
cache. display dns host ip
[ | { begin | exclude |
include } regular-expression ] Available in any view
Clear the information of the
dynamic IPv4 domain name
cache. reset dns host ip
Available in user view
Static domain name resolution configuration
example
Network requirements
As shown in Figure 42, the device wants to ac cess the host by us i ng an e asy- to - remember domai n name
rather than an IP address.
Configure static domain name resolution on the de vice so that the device can use the domain name
host.com to access the host whose IP address is 10.1.1.2.
Figure 42 Network diagram
Configuration procedure
# Configure a mapping between host name host.com and IP address 10.1.1.2.
92
system-view
[Sysname] ip host host.com 10.1.1.2
# Use the ping host.com command to verify that the device can use static domain name resolution to
resolve domain name host.com into IP address 10.1.1.2.
[Sysname] ping host.com
PING host.com (10.1.1.2):
56 data bytes, press CTRL_C to break
Reply from 10.1.1.2: bytes=56 Sequence=1 ttl=128 time=1 ms
Reply from 10.1.1.2: bytes=56 Sequence=2 ttl=128 time=4 ms
Reply from 10.1.1.2: bytes=56 Sequence=3 ttl=128 time=3 ms
Reply from 10.1.1.2: bytes=56 Sequence=4 ttl=128 time=2 ms
Reply from 10.1.1.2: bytes=56 Sequence=5 ttl=128 time=3 ms
--- host.com ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 1/2/4 ms
Dynamic domain name resolution configuration
example
Network requirements
As shown in Figure 43, t h e d evic e wa nt s to a c c ess t h e hos t by us i n g a n e asy - to - re m e mb e r d o m a i n n a m e
rather than an IP address, and to request the DNS server on the network for an IP address by using
dynamic domain name resolution. The IP address of the DNS server is 2.1.1.2/16 and the DNS server has
a com domain, which stores the mapping between domain name host and IP address 3.1.1.1/16.
Configure dynamic domain name resolution and the do main name suffix com on the device that serves
as a DNS client so that the device can use domain name host to access the host with the domain name
host.com and the IP address 3.1.1.1/16.
Figure 43 Network diagram
93 Configuration procedure Before performing the following configuration, make sure that the device and the host are accessible to each other via available routes, and that the IP addresses of the interfaces are configured as shown Figure 43 . T his configuration may vary with DNS servers. The following configuration is performed on a PC running Windows Server 2000. 1. Configure the DNS server: a. Select Start > Programs > Administrative Tools > DNS . The DNS server configuration page appears, as shown in Figure 44. b. Right click Forward Lookup Zones , select New Zone, and then follow the steps to create a new zone named com. Figure 44 Creating a zone a. On the DNS server configuration page, right click zone com, and select New Host.
94 Figure 45 Adding a host d. On the page that appears, enter host name host and IP address 3.1.1.1. e. Click Add Host . The mapping between the IP address and host name is created. Figure 46 Adding a mapping between domain name and IP address 2. Configure the DNS client:
95
# Enable dynamic domain name resolution.
system-view
[Sysname] dns resolve
# Specify the DNS server 2.1.1.2.
[Sysname] dns server 2.1.1.2
# Configure com as the name suffix.
[Sysname] dns domain com
Verifying the configuration
# Use the ping host command on the device to verify that the communication between the device and the
host is normal and that the corresponding destination IP address is 3.1.1.1.
[Sysname] ping host
Trying DNS resolve, press CTRL_C to break
Trying DNS server (2.1.1.2)
PING host.com (3.1.1.1):
56 data bytes, press CTRL_C to break
Reply from 3.1.1.1: bytes=56 Sequence=1 ttl=126 time=3 ms
Reply from 3.1.1.1: bytes=56 Sequence=2 ttl=126 time=1 ms
Reply from 3.1.1.1: bytes=56 Sequence=3 ttl=126 time=1 ms
Reply from 3.1.1.1: bytes=56 Sequence=4 ttl=126 time=1 ms
Reply from 3.1.1.1: bytes=56 Sequence=5 ttl=126 time=1 ms
--- host.com ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 1/1/3 ms
DNS proxy configuration example
Network requirements
When the IP address of the DNS server changes, you must configure the new IP address of the DNS
server on each device on the LAN. To simplify network management, you can use the DNS proxy
function.
As shown in Figure 47:
• S
pecify Device A as the DNS server of Device B (the DNS client). Device A acts as a DNS proxy.
The IP address of the real DNS server is 4.1.1.1.
• Configure the IP address of the DNS proxy on Device B. DNS requests of Device B are forwarded
to the real DNS server through the DNS proxy.
96 Figure 47 Network diagram Configuration procedure Before performing the following configuration, assume that Device A, the DNS server, and the host are reachable to each other and the IP addresses of the interfaces are configured as shown in Figure 47. 1. Configure the DNS server: This configuration may vary with different DNS servers. When a PC running Windows Server 2000 acts as the DNS server, see Dynamic domain name resolution configuration example for related configu ration information. 2. Configure the DNS proxy: # Specify the DNS server 4.1.1.1. system-view [DeviceA] dns server 4.1.1.1 # Enable DNS proxy. [DeviceA] dns proxy enable 3. Configure the DNS client: # Enable the domain name resolution function. system-view [DeviceB] dns resolve # Specify the DNS server 2.1.1.2. [DeviceB] dns server 2.1.1.2 Verifying the configuration # Execute the ping host.com c o m m a n d o n D evic e B to veri f y t h a t t h e c om mu n ic a t io n b e t we e n t h e devic e and the host is normal and that the corresponding destination IP address is 3.1.1.1. [DeviceB] ping host.com Trying DNS resolve, press CTRL_C to break Trying DNS server (2.1.1.2) PING host.com (3.1.1.1): 56 data bytes, press CTRL_C to break
97
Reply from 3.1.1.1: bytes=56 Sequence=1 ttl=126 time=3 ms
Reply from 3.1.1.1: bytes=56 Sequence=2 ttl=126 time=1 ms
Reply from 3.1.1.1: bytes=56 Sequence=3 ttl=126 time=1 ms
Reply from 3.1.1.1: bytes=56 Sequence=4 ttl=126 time=1 ms
Reply from 3.1.1.1: bytes=56 Sequence=5 ttl=126 time=1 ms
--- host.com ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 1/1/3 ms
Troubleshooting IPv4 DNS configuration
Symptom
After enabling dynamic domain name resolution, the user cannot get the correct IP address.
Solution
1. Use the display dns host ip command to verify that the specified domain name is in the cache.
2. If the specified domain name does not exist, ve rify that dynamic domain name resolution is
enabled and that the DNS client can communicate with the DNS server.
3. If the specified domain name is in the cache, bu t the IP address is incorrect, verify that the DNS
client has the correct IP address of the DNS server.
4. Verify that the mapping between the domain name and IP address is correct on the DNS server.
98 Configuring IRDP Overview As an extension of the Internet Control Message Protocol (ICMP), the ICMP Router Discovery Protocol (IRDP) enables hosts to discover the IP addresses of their neighboring routers and set their default routes. NOTE: The hosts in this chapter support IRDP. Background Before a host can send packets to another network, it must know the IP address of at least one router on the local subnet. The host can obtain this information either through manual configuration, or from routing protocol packets sent by routers on the local subnet. Both methods have disadvantages. The first method requires the administrator to manually configure and maintain router address information on hosts, and cannot track dynamic changes. The second method requires hosts to recognize various routing protocols, an d will fail to work if no routing protocol runs on the local subnet. IRDP was introduced to solve the problem. IRDP uses two new types of ICMP messages to allow hosts to discover neighboring routers. IRDP adapts to dynamic changes, requires less manual configuration, and does not rely on any routing protocols. Working mechanism IRDP uses the following types of ICMP messages. • Router advertisement (RA) —Sent by a router to advertise its IP address and preference. • Router solicitation (RS) —Sent by a host to voluntarily reques t the IP addresses of routers on the subnet. IRDP operates in the following steps: 1. A router periodically broadcasts or multicasts an RA, which contains the IP addresses (including the primary IP address and manually configured secondary IP addresses) of in terfaces. Hosts listen for RAs to obtain the IP addresses of neighboring routers. 2. Rather than wait for RAs, a newly attached host can voluntarily send an RS to request immediate RAs for the IP addresses of routers on the subnet. If no response to the RS is received, the host retransmits the RS several ti mes. If the host still receives no RA s, it will obtain the IP addresses of routers from periodic RAs. 3. Upon receiving an RA, a host adds the IP addresses in the RA to its routing table. The host selects the IP address with the highest preference am ong all obtained IP addresses as the default gateway. IRDP allows hosts to locate routers, but does not sugges t the best route to a specific destination. If a host selects a router that is not the best next hop to a sp ecific destination, the router will send back an ICMP redirect message to provide a better next hop.