network unreachable resolving

If you are receiving the error in /var/log/messages for named service as follows.

Error::

Quote:

Feb 23 15:44:49 named[28471]: network unreachable resolving 'L.ROOT-SERVERS.NET/AAAA/IN': 2001:503:ba3e::2:30#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'G.ROOT-SERVERS.NET/AAAA/IN': 2001:dc3::35#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'L.ROOT-SERVERS.NET/AAAA/IN': 2001:503:c27::2:30#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'G.ROOT-SERVERS.NET/AAAA/IN': 2001:7fd::1#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'I.ROOT-SERVERS.NET/AAAA/IN': 2001:dc3::35#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'D.ROOT-SERVERS.NET/AAAA/IN': 2001:dc3::35#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'I.ROOT-SERVERS.NET/AAAA/IN': 2001:7fd::1#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'E.ROOT-SERVERS.NET/AAAA/IN': 2001:dc3::35#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'L.ROOT-SERVERS.NET/AAAA/IN': 2001:dc3::35#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'B.ROOT-SERVERS.NET/AAAA/IN': 2001:503:c27::2:30#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'L.ROOT-SERVERS.NET/AAAA/IN': 2001:7fd::1#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'C.ROOT-SERVERS.NET/AAAA/IN': 2001:503:c27::2:30#53

Feb 23 15:44:49 named[28471]: network unreachable resolving 'B.ROOT-SERVERS.NET/AAAA/IN': 2001:dc3::35#53

Cause:

As per the change log of BIND for CentOS 5.4 updates (bind-chroot-9.3.6-4.P1.el5_4.1) , the latest BIND DNS server is enabled by default for IPV6 DNS resolving. Any DNS query made to the DNS server will caused the program to also resolved IPV6 IP regardless that the host server or client is not IPV6 enable or capable.

Solution:

Disable the IPV6 in BIND by editing the file /etc/sysconfig/named file and adding the following options into the BIND startup

# vim /etc/sysconfig/named

OPTIONS="-4"

:wq

This will cause the BIND server to only resolve or use IPV4 and disable IPV6 support. Save the file and restart BIND server.

# /etc/init.d/named restart

Read more...

Bonding (Port Trunking)

Bonding is the same as port trunking. In the following I will use the word bonding because practically we will bond interfaces as one.

Bonding:

Bonding allows you to aggregate multiple ports into a single group, effectively combining the bandwidth into a single connection. Bonding also allows you to create multi-gigabit pipes to transport traffic through the highest traffic areas of your network. For example, you can aggregate three megabits ports (1 mb each) into a three-megabits trunk port. That is equivalent with having one interface with three megabits speed.

Read more...

Disable the Telnet server

To disable the Telnet server:
Go to the /etc/xinetd.d/telnet and make disable = Yes. Start the xinetd service.


#vi /etc/xinetd.d/telnet
Disable = Yes
:wq


# service xinetd restart

Read more...

PING command

PING:


PING stands for Packet Internet Groper. This is the tool that diagnosis ICMP protocols troubles on ICMP network. Within TCP/IP there are many protocols(i.e TCP, UDP, etc..). There is one protocols sweep in TCP protocol is called ICMP(Internet Control Messaging Protocol) protocol. It is regularly designed for facilitate troubleshooting or diagnosing problems of IP based network.

To view the full path of ping command:
#which ping
/bin/ping

To view the package of the ping command:
#rpm -qf ping
iputils-200020927-2

Ping on a client or on host or on server realize on client interface to the ICMP protocol. So when pinging on host functioning as client. The host that responses functioning as server to response on our request. When you ping a host or requests to the host then it is called an echo request  and when host replies then it is called an echo reply.

Ping function as client server protocol. ping is used for diagnosis and also used for DNS resolution (It is way to test whether the DNS resolution is working or not).

#ping www.yahoo.com

It's going on responding util pressing the Ctrl+c. When
Unless we break the process using Ctrl+c or It never end. Ping sends packets within one second

If name resulotion is not functioning on this machine, the response will not come back. Then see the name resolution settings. Those name resolutions are responding. So then to test the name resolution on your system simply use the dig and nslookup tools. It is another way to ping the host.

To send only 3 pings to server instead of sending indefinite number of times:
#ping -c 3 www.yahoo.com

To send only 6 pings to server:

#ping -c 6 www.yahoo.com

if any sort of firewalls or routers at the edge of the network prevents ping echo requests type8 and also it prevents echo response type0 from leaving the network consequently we can ping the network  in between our machine and other machine which you want to ping. Then chances are ping will work. Does mean that host is down. It simply means the ICMP is been blocked. 

Read more...