Henry's Points

Sadly, I heard nslookup will be gone with the wind. But luckily, we have dig to get more detailed information about domain name. The following are comparison of two commands for www.google.com

[root@hengdu ~]# dig www.google.com

; <<>> DiG 9.5.0b1 <<>> www.google.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 37711
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 7, ADDITIONAL: 7

;; QUESTION SECTION:
;www.google.com. IN A

;; ANSWER SECTION:
www.google.com. 105861 IN CNAME www.l.google.com.
www.l.google.com. 300 IN A 66.249.91.99
www.l.google.com. 300 IN A 66.249.91.103
www.l.google.com. 300 IN A 66.249.91.104
www.l.google.com. 300 IN A 66.249.91.147

;; AUTHORITY SECTION:
l.google.com. 24160 IN NS e.l.google.com.
l.google.com. 24160 IN NS f.l.google.com.
l.google.com. 24160 IN NS g.l.google.com.
l.google.com. 24160 IN NS a.l.google.com.
l.google.com. 24160 IN NS b.l.google.com.
l.google.com. 24160 IN NS c.l.google.com.
l.google.com. 24160 IN NS d.l.google.com.

;; ADDITIONAL SECTION:
a.l.google.com. 24373 IN A 209.85.139.9
b.l.google.com. 24255 IN A 64.233.179.9
c.l.google.com. 24160 IN A 64.233.161.9
d.l.google.com. 24373 IN A 66.249.93.9
e.l.google.com. 24311 IN A 209.85.137.9
f.l.google.com. 38846 IN A 72.14.235.9
g.l.google.com. 24553 IN A 64.233.167.9

;; Query time: 13 msec
;; SERVER: 65.39.139.53#53(65.39.139.53)
;; WHEN: Tue Feb 19 10:40:52 2008
;; MSG SIZE rcvd: 340

[root@hengdu ~]# nslookup www.google.com
Server: 65.39.139.53
Address: 65.39.139.53#53

Non-authoritative answer:
www.google.com canonical name = www.l.google.com.
Name: www.l.google.com
Address: 66.249.91.147
Name: www.l.google.com
Address: 66.249.91.99
Name: www.l.google.com
Address: 66.249.91.103
Name: www.l.google.com
Address: 66.249.91.104

Tags: How-to by hengdu
No Comments »

Due to testing on the network, the package lost rate is needed. The following bash script shows how to get percentage of package loss. I split IP address to four segments since it will be easy to manipulate for loop.

PINGTMP=/tmp/ping.tmp

IP_1=`echo $IPADDRESS | awk -F”.” ‘{print $1}’`
IP_2=`echo $IPADDRESS | awk -F”.” ‘{print $2}’`
IP_3=`echo $IPADDRESS | awk -F”.” ‘{print $3}’`
IP_4=`echo $IPADDRESS | awk -F”.” ‘{print $4}’`
ping -t 5 -c 2 $IP_1.$IP_2.$IP_3.$IP_4 > $PINGTMP
pack_loss=`awk ‘/statistics/{getline;print $6}’ $PINGTMP`
echo $pack_loss

Tags: Coding, How-to, Linux by hengdu
No Comments »

One Linux computer box could be as a router if it has more than one NIC. Howerver, it would not forward packages as normal router does. Here is a simple example: Host1—Host2—Host3. Host2 will be router to let Host1 connects to Host3. You may find out Host1 cannot PING Host3. To solve it, there are two ways to enable ip_forward on Host2.

1. Simple but will lost at next reboot

echo 1 > /proc/sys/net/ipv4/ip_forward

2. Change Configuration at next reboot
“vi /etc/sysctl.conf ” to change following configuration:

# Controls IP packet forwarding
net.ipv4.ip_forward = 1

Of course, the best way to enable IP forwarding is to configure iptables, which will be more secured.

Tags: How-to, Linux by hengdu
No Comments »