Networker's BLOG

Sunday, March 30, 2008

Tutorials

How To: DHCP Server (1)
How To: DHCP Server Logs (1)
How To: MySQL Server Installation (1)
How To: Apache Web Server (1)
How To: Caching DNS (1)
How To: IPTABLES Configuration (1)
How To: IPTABLES Installation (1)
How To: IPTABLES Scenario 1 (1)
How To: IPTABLES Scenario 1.1 (1)
How To: IPTABLES Scenario 2 (1)
How To: IPTABLES Scenario 2.1 (1)
How To: IPTABLES Tip (1)
How To: PHP (1)
How To: Squid Proxy (1)
How To: Squid Proxy Authentication (1)
How To: Squid Proxy Restricting Site (1)
How To: Squid Proxy Transparent (1)
How To: Squid Proxy using ACL (1)
How To: VSFTP Server (1)

Network Tip No. 40: Show Available Memory

Show Used and Available Memory of your Cisco router or switch

A router can be limited by its available memory. To show the used and available memory,

Router#show proc mem

At the beginning of the output, look for a line like this:

Total: 200234528, Used: 70508188, Free: 129726340

Network Tip No. 39: Show Processor Load

Show proccessor load of your router or switch,which can be limited by its processing power. To show the processor utilization,

Router#show proc cpu
At the beginning of the output, look for a line like this:

CPU utilization for five seconds: 37%/30%; one minute: 39%; five minutes: 40%

Network Tip No. 38: CLI Editing Tips

Learn the command-line editing keys.

Control A Goes to the beginning of the line
Control E Goes to the end of the line
Control K Deletes everything to the right of the cursor
Control P Recalls the previous command in the history buffer
Control N Recalls the next command in the history buffer

Network Tip No. 37: ACL on DNS

No browsing....

A common access-list pitfall is when people forget to allow DNS (Domain Name Servers) from their internal network to the provider's DNS servers. Mainly this is a problem on home or small office routers where you might not have an internal DNS server running.

The following command allows DNS access from your hosts to the outside DNS server. In this example, our outside DNS servers are 192.168.30.11 and 192.168.30.12


  access-list 110 permit udp host 192.168.30.11 eq domain any gt 1023
  access-list 110 permit udp host 192.168.30.12 eq domain any gt 1023

Network Tip No. 36: ACL on ICMP

Some are having some problems on the ICMP access-list. Try this one

allow pings into the network
   access-list 110 permit icmp any any echo
   ! allow ping responses
   access-list 110 permit icmp any any echo-reply
   ! allow ICMP source-quench
   access-list 110 permit icmp any any source-quench
   ! allow path MTU discovery
   access-list 110 permit icmp any any packet-too-big
   ! allow time-exceeded, which is useful for traceroute
   access-list 110 permit icmp any any time-exceeded
   ! deny all other ICMP packets
   access-list 110 deny icmp any any

Network Tip No. 35: Stopping the router from crazy output

Stopping the router from crazy output...

An annoying problem output everytime you mistype a command and the router thinks you just typed a hostname. For example:


  Router#shwo
  Translating "shwo"...domain server (10.1.1.1)
  % Unknown command or computer name, or unable to find computer address
  Router#

The way to handle this is to change the preferred transport method:


  ! Console port
  line con 0
      transport preferred none
  ! VTY Ports
  line vty 0 5
      transport preferred none

The output shows the lack of a failed connection based on our mistyped keyword:


  Router#shwo
      ^
  % Invalid input detected at '^' marker.

Network Tip No. 34: The reload command

When everything fails.... hehe


   Router#reload in 3
       Reload scheduled in 3 minutes
   Proceed with reload? [confirm]y

Wednesday, March 26, 2008

Linux Tip No. 36: How to Enable IP Forwarding

Enable IP Forwarding

1. Check if IP Forwarding is enabled

Using sysctl:

[root@proxy ~]# sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 0

or just checking out the value in the /proc system:

[root@proxy ~]# cat /proc/sys/net/ipv4/ip_forward
0

Value 0 means it is disabled.

2. Enable IP Forwarding on the fly

[root@proxy ~]#sysctl -w net.ipv4.ip_forward=1

[root@proxy ~]#echo 1 > /proc/sys/net/ipv4/ip_forward

the setting is changed instantly; the result will not be preserved after rebooting the system.

3. Permanent setting using /etc/sysctl.conf

If we want to make this configuration permanent the best way to do it is using the file /etc/sysctl.conf where we can add a line containing net.ipv4.ip_forward = 1

[root@proxy ~]#vi /etc/sysctl.conf 
# Controls IP packet forwarding
net.ipv4.ip_forward = 1

if you already have an entry net.ipv4.ip_forward with the value 0 you can change that 1.

To enable the changes made in sysctl.conf you will need to run the command:

[root@proxy ~]#sysctl -p /etc/sysctl.conf

Restart the network service

[root@proxy ~]#service network restart

Linux Tip No. 35: Enable service at boot up

To Check:
[root@jepoy ~]# chkconfig --list |grep httpd
httpd 0:off 1:off 2:on 3:on 4:on 5:on 6:off

To enable at boot up:
[root@jepoy ~]# chkconfig httpd on

Linux Tip No. 34: How to Check Services

This command is used to start/stop your services.

service   start/stop/restart/status

To Start:
[root@jepoy ~]# service httpd start

To Stop:
[root@jepoy ~]# service httpd stop

To Restart:
[root@jepoy ~]# service httpd restart

To check:
[root@jepoy ~]# service httpd status

Monday, March 24, 2008

Linux Tip No. 33: How to check your DHCP server

This command tells you what DHCP server you are using.

[root@jepoy ~]# grep dhcp-server-identifier /var/lib/dhcp/dhclient.leases
option dhcp-server-identifier 192.168.0.254;

Linux Tip No. 32: Checking the top 10 directories

Top 10 directories eating up your disk space:

[root@mail etc]# du -cksh * | sort -rn | head -10
852K sysconfig
784K termcap
704K selinux
704K makedev.d
632K firmware
552K X11
544K pam.d
472K prelink.cache
460K alsa
444K postfix

Linux Tip No. 31: Renew/Release DHCP client

[root@proxy ~]# dhclient -r

[root@proxy ~]# dhclient
Internet Systems Consortium DHCP Client V3.0.2
Copyright 2004 Internet Systems Consortium.
All rights reserved.
For info, please visit http://www.isc.org/products/DHCP

The -r flag
explicitly releases the current lease, and once the lease has been released, the client exits.

Sunday, March 23, 2008

Network Tip No. 33: Troubleshootin IGRP

Troubleshooting IGRP Issues

Router#debug ip igrp events	Shows all IGRP events in real time
Router#debug ip igrp transactions	Shows IGRP updates between routers

Network Tip No. 32: IGRP Routing Optional Commands

IGRP Routing: Optional Commands

`Router(config)#no router igrp` `as-number`	Disables the IGRP routing process
`Router(config-router)#no network` `w.x.y.z`	Removes network w.x.y.z from the IGRP routing process
`Router(config-if)#bandwidth` `x`	Sets the bandwidth of this interface to x kilobits to allow IGRP to make a better routing decision
`Router(config-router)#variance` `x`	Allows IGRP to accept unequal-cost routes

Network Tip No. 31: IGRP Routing Commands

IGRP Routing: Mandatory Commands

Router(config)#router igrp as-number	Enables IGRP routing process. The autonomous system number (AS-number) used in the IGRP routing process must match all other routers that are going to share routing updates in order for communication to take place
Router(config-router)#network w.x.y.z	w.x.y.z is the network number of the directly connected network you want to advertise

Note:

You need to advertise only the classful network number, not a subnet:

Router(config-router)#network 172.17.0.0

not

Router(config-router)#network 172.17.10.0

If you advertise a subnet, you will not receive an error message, because the router will automatically convert the subnet to the classful network address.