Solution to problem 29 from Project Euler. Also written in Python as my previous post.
#!/usr/bin/env python
# Project Euler problem 29
list = []
for a in range(2, 101):
for b in range(2, 101):
product = a ** b
list.append(product)
list.sort()
newlist = sorted(set(list))
print len(newlist)
Below is the solution to problem 30 from Project Euler. It’s written in Python, a programming language I’m trying to learn.
#!/usr/bin/env python
# Project Euler problem 30
narc_sum = 0
for number in range(100, 200000):
# Transform the number into a string
string = str(number)
# Transform the string into a list
lst = list(string)
sum = 0
for i in range(len(lst)):
# Add the members of the list to the fifth power
sum = sum + (int(lst[i])**5)
if (number == sum):
# Add all numbers and store in narc_sum value
narc_sum = narc_sum + number
print "Sum is ",narc_sum
So the other day I was looking around and discovered the notify-send command. It basically sends notifications to the desktop. Pretty useful now adays.
[11:49:13] xavi@thinkpad: ~ $ sudo dpkg -S `which notify-send`
libnotify-bin: /usr/bin/notify-send
[11:49:15] xavi@thinkpad: ~ $
It is installed with libnotify-bin via aptitude.
[11:50:35] xavi@thinkpad: ~ $ sudo aptitude install libnotify-bin
So, once installed lets create a practical script. On my job I need to have a permanente VPN connection. Once in a while the VPN connection drops and we have to connect again. Lets create a simple script that notifies us when the connection drops.
#!/bin/bash
# Check tunnel interface
while "true"; do
/sbin/ifconfig tun0 &> /dev/null
while [ $? -ne 0 ]; do
notify-send -t 5000 "VPN" "VPN is down"
done
sleep 300
done
We save and copy the script, give it execution permissions with chmod and send it to background.
[11:55:47] xavi@thinkpad: ~ $ chmod +x /tmp/check-vpn.sh; /tmp/check-vpn.sh &
[1] 15613
[12:00:43] xavi@thinkpad: ~ $
Here is a screenshot of it working.
Enjoy.
So lets say you want to see how many established connections we have on a particular port/service. Most of the people would use netstat, however I prefer ss.
On a Debian based system ss can be installed with the iproute package.
user@server: ~ $ sudo dpkg -S `which ss` iproute: /sbin/ss user@server: ~ $
On a Red Hat based system it will be installed with iproute too.
[user@redhat ~]# sudo rpm -qf `which ss` iproute-2.6.18-11.el5 [user@redhat ~]#
aptitude install iproute and yum install iproute will install the package on a Debian and Red Hat system respectively.
Now lets show some examples. Lets say we want to see how many established ssh connections there are.
[user@redhat ~]# sudo ss -t '( sport = :22 )' State Recv-Q Send-Q Local Address:Port Peer Address:Port ESTAB 0 0 ::ffff:10.40.7.12:ssh ::ffff:10.16.241.194:56325 ESTAB 0 0 ::ffff:10.40.7.12:ssh ::ffff:10.16.241.194:53804 ESTAB 0 0 ::ffff:10.40.7.12:ssh ::ffff:10.16.241.194:60486 ESTAB 0 0 ::ffff:10.40.7.12:ssh ::ffff:10.14.17.48:37471 ESTAB 0 0 ::ffff:10.40.7.12:ssh ::ffff:10.16.241.194:57982 ESTAB 0 0 ::ffff:10.40.7.12:ssh ::ffff:10.16.241.194:57525 ESTAB 0 304 ::ffff:10.40.7.9:ssh ::ffff:10.14.17.22:46376 ESTAB 0 0 ::ffff:10.40.7.9:ssh ::ffff:10.16.241.28:42654 ESTAB 0 0 ::ffff:10.40.7.9:ssh ::ffff:10.16.241.12:36276 ESTAB 0 0 ::ffff:10.40.7.9:ssh ::ffff:10.16.241.8:57936 ESTAB 0 0 ::ffff:10.40.7.9:ssh ::ffff:10.16.241.28:42855 [user@redhat ~]#
-t displays all TCP sockets
You can also substitute the port number by the name of the service that runs in it by default.
user@debian:~$ sudo ss -t '( sport = :mysql )' State Recv-Q Send-Q Local Address:Port Peer Address:Port ESTAB 0 0 192.168.140.121:mysql 192.168.137.234:35512 user@debian:~$
To see all opened ports on the server use the -a option.
xavi@linode2:~$ sudo ss -t -a State Recv-Q Send-Q Local Address:Port Peer Address:Port LISTEN 0 5 *:nrpe *:* LISTEN 0 50 192.168.140.121:mysql *:* LISTEN 0 8 *:pop3 *:* LISTEN 0 8 *:imap2 *:* LISTEN 0 128 :::www :::* LISTEN 0 128 *:ssh *:* LISTEN 0 128 :::ssh :::* LISTEN 0 100 *:smtp *:* LISTEN 0 128 :::https :::* TIME-WAIT 0 0 ::ffff:173.255.231.252:www ::ffff:79.158.142.28:55032 ESTAB 0 0 192.168.140.121:mysql 192.168.137.234:35512 ESTAB 0 48 173.255.231.252:ssh 79.158.142.28:48395 TIME-WAIT 0 0 ::ffff:173.255.231.252:www ::ffff:79.158.142.28:55033 TIME-WAIT 0 0 ::ffff:173.255.231.252:www ::ffff:173.255.231.252:37223 xavi@linode2:~$
I believe ss command is simpler to use but less known than netstat. Enjoy.
So now we need to configure a cloud to connect GNS3 to the laptop. We should already have tap0 up and running and IPtables configured to allow traffic as seen on the previous post.
Below is a network topology diagram.
We need to create the cloud connecting it to tap0 interface. For that we edit the .net file containing the topology and add the following.
[[ROUTER R2]]
model = 3640
console = 2002
aux = 2108
cnfg = configs/R2.cfg
slot0 = NM-1FE-TX
f0/0 = nio_tap:tap0
slot1 = NM-4T
s1/0 = R3 s1/0
slot2 = NM-1E
e2/0 = R1 f2/0
slot3 = NM-16ESW
x = -21.0
y = -61.0
and for the cloud
[[Cloud C2]]
x = -63.8566172588
y = 84.919044975
connections = R2:f0/0:nio_tap:tap0
Now save the configuration and restart GNS3.
Now there should be connectivity to the gateway (192.168.1.1). To connect to the internet add a default gateway.
Router2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Router2(config)#ip rou
Router2(config)#ip route
Router2(config)#ip route 0.0.0.0 0.0.0.0 192.168.1.1
Router2(config)#do sh ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
E1 – OSPF external type 1, E2 – OSPF external type 2
i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
ia – IS-IS inter area, * – candidate default, U – per-user static route
o – ODR, P – periodic downloaded static route
Gateway of last resort is 192.168.1.1 to network 0.0.0.0
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.0.0/30 is directly connected, Ethernet2/0
D 172.16.0.0/16 is a summary, 00:18:32, Null0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.0.0.0/30 is directly connected, Serial1/0
D 10.0.0.0/8 is a summary, 00:18:32, Null0
192.168.1.0/30 is subnetted, 1 subnets
C 192.168.1.0 is directly connected, FastEthernet0/0
S* 0.0.0.0/0 [1/0] via 192.168.1.1
Router2(config)#
We can see the connectivity below.
Also don’t forget to add the routes on your Linux box for the other routers.
[11:07:13] xavi@lstkco14073: ~ $ sudo ip route add 172.16.0.0/30 dev tap0
[11:07:49] xavi@lstkco14073: ~ $ sudo ip route add 10.0.0.0/30 dev tap0
[11:08:13] xavi@lstkco14073: ~ $ netstat -nr | grep tap
10.0.0.0 0.0.0.0 255.255.255.252 U 0 0 0 tap0
172.16.0.0 0.0.0.0 255.255.255.252 U 0 0 0 tap0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 tap0
[11:08:21] xavi@lstkco14073: ~ $ ping -c 3 10.0.0.1
PING 10.0.0.1 (10.0.0.1) 56(84) bytes of data.
64 bytes from 10.0.0.1: icmp_req=1 ttl=255 time=19.9 ms
64 bytes from 10.0.0.1: icmp_req=2 ttl=255 time=3.12 ms
64 bytes from 10.0.0.1: icmp_req=3 ttl=255 time=6.61 ms
— 10.0.0.1 ping statistics —
3 packets transmitted, 3 received, 0% packet loss, time 2001ms
rtt min/avg/max/mdev = 3.122/9.878/19.901/7.229 ms
[11:08:39] xavi@lstkco14073: ~ $
That would be all. Comments and suggestions are more than welcome. 🙂