RH133读书笔记(8)-Lab 8 Manage Network Settings

Lab 8 Manage Network Settings

Goal: To build skills needed to manually configure networking

Estimated Duration: 45 minutes

System Setup: A Red Hat Enterprise Linux System using DHCP networking

Lab Setup: Disable the DHCP service on server1.

Sequence 1: Setting up a static IP address

Scenario: The DHCP server is down! You need to get your workstation up on the network, so you have to edit the appropriate configuration files by hand to set up static networking.

Deliverable: A system configured to operate with static rather than dynamic network settings.

Instructions:

1. Current Settings

What is your current IP address and subnet mask

[root@stationX ~]# ip addr show

What is your current default gateway

[root@stationX ~]# ip route show

What is your current DNS Name Server

[root@stationX ~]# cat /etc/resolv.conf

2. Shut Down Interface

[root@stationX ~]# ifdown eth0

Shut down your interface

3. Define Layer 3 Static Settings

Edit the configuration file of the eth0 device, so that it uses the IP Address, Network Mask, and Default Gateway settings recorded above.

Open /etc/sysconfig/network-scripts/ifcfg-eth0 in a text editor and add or edit the following lines (where X is replaced with your station number). Leave other existing lines alone (like HWADDR):

DEVICE=eth0
BOOTPROTO=none
ONBOOT=yes
IPADDR=192.168.0.X
NETMASK=255.255.255.0
GATEWAY=192.168.0.254

4. Verify DNS and Hostname Resolution

Verify that your system is still using the recorded name server from above.

[root@stationX ~]# cat /etc/resolv.conf
search example.com
nameserver 192.168.0.254

Make sure that your hostname is set to stationX.example.com and that this hostname is used automatically at boot.

[root@stationX ~]# hostname
stationX.example.com

Open /etc/sysconfig/network in a text editor and ensure that the HOSTNAME variable is properly set:

HOSTNAME=stationX.example.com

Verify that your hostname can be resolved to the correct IP address without using DNS.

Open /etc/hosts in a text editor and ensure that the following lines appear:

127.0.0.1 localhost.localdomain localhost
::1 localhost6.localdomain6 localhost6
192.168.0.X stationX.example.com stationX

5. Test new settings

Bring up your newly-configured interface and verify that your settings work.

[root@stationX ~]# ifup eth0
[root@stationX ~]# ping server1

Make sure that this configuration also works after a reboot.

[root@stationX ~]# shutdown -r now
[root@stationX ~]# ping server1

Sequence 2: Virtual IP Addresses and Static Routes

Scenario: A network service will be installed on your system. You have decided to use a virtual IP address for this service to be more flexible in the future.

Your coworker has likewise created a virtual IP address that is not routed by your gateway but which you need to gain access.

Deliverable: An additional virtual IP address available after reboot.

A static route to support access to virtual IP address of your neighbor.

System Setup: Work together with a partner. Your virtual IP address will be 10.0.X.1/24(where X is your station number). The virtual IP address of your neighbor will be 10.0.Y.1/24 (where Y is the station number of your neighbor).

Instructions:

1. Create IP alias
Configure your system with a new device alias named eth0:1 so that it uses the additional IP address 10.0.X.1 with a network mask of 255.255.255.0. This IP should also be available after reboot.

• Create /etc/sysconfig/network-scripts/ifcfg-eth0:1 in a text editor and enter the following lines (where X is your station number):

DEVICE=eth0:1
BOOTPROTO=none
ONBOOT=yes
IPADDR=10.0.X.1
NETMASK=255.255.255.0

• To verify, either reboot the system or simply activate the new device.

[root@stationX ~]# shutdown -r now

or

[root@stationX ~]# ifup eth0:1

• Test that the new interface responds locally.

[root@stationX ~]# ping 10.0.X.1

2. Create Static Route to Neighbor Alias

Create a static route to the alias network of your neighbor via the regular IP address of your neighbor:

network 10.0.Y.0/255.255.255.0 through gateway 192.168.0.Y

Make this route permanent so that it persists across reboots.

• Start by adding the following route manually:

network 10.0.Y.0/255.255.255.0 through gateway 192.168.0.Y

Note: If you have not used the ip command before, this is an excellent time to begin using it. Check ip(8) if you do not know the syntax.

[root@stationX ~]# ip route add 10.0.Y.0/24 via 192.168.0.Y

• Verify this new route.

View the current routing table to confirm the above line was added:

[root@stationX ~]# ip route
10.0.Y.0/24 via 192.168.0.Y dev eth0

See if you can access the remote network by trying to access the device alias of your neighbor:

[root@stationX ~]# ping -c 4 10.0.Y.1

• Make this route permanent and then restart networking to verify your changes persist.

Create a file named /etc/sysconfig/network-scripts/route-eth0 with the following content:

10.0.Y.0/24 via 192.168.0.Y

Restart networking

[root@stationX ~]# service network restart

Test that remote alias is still available

[root@stationX ~]# ping -c 4 10.0.Y.1

Sequence 3: Troubleshooting Slow DNS

Scenario: Our users are complaining about slow network response from this system with no additional details.

Instructions:

1. Break DNS

Modify the list of nameservers to contain a total of three: 192.168.0.X, 192.168.1.X, 192.168.0.254, in that specific order, where X is your station number.

Open /etc/resolv.conf in a text editor and ensure that the following lines appear (in the same sequence, replacing X with your station number):

search example.com
nameserver 192.168.0.X
nameserver 192.168.1.X
nameserver 192.168.0.254

2. Symptoms

Try pinging 192.168.0.254. It should be successful and the first ping should be almost immediate.

[root@stationX ~]# ping -c 4 192.168.0.254

Try pinging the same machine, but using its name, server1.example.com. The operation should be successful, but should have paused for a couple of seconds before transmitting and reporting the first ping response.

[root@stationX ~]# ping -c 4 server1

This should lead us to a determination that something is wrong with name resolution.

3. Troubleshoot and Fix

Test DNS connectivity with dig. What DNS Server is responding with an answer

[root@stationX ~]# dig server1.example.com

Compare the reported DNS server to the list of nameservers configured on this system. In what position is the reported name server

[root@stationX ~]# cat /etc/resolv.conf

The client resolver uses the list of nameservers in a fixed sequence every time. Hence the delay in resolving since the first two entries are not “responding”.

Fix the list of nameservers by returning it back to its original state.

Open /etc/resolv.conf in a text editor and ensure that the following lines appear:

search example.com
nameserver 192.168.0.254