How to recover IOS from ROMMON

rommon 1 > IP_ADDRESS=172.30.10.20 (gives IP address to current device)

rommon 2 > IP_SUBNET_MASK=255.255.255.0

rommon 3 > DEFAULT_GATEWAY=172.30.10.1

rommon 4 > TFTP_SERVER=172.30.10.100

rommon 5 > TFTP_FILE=c3640-jk9o3s-mz.123-14.T7.bin

rommon 6 > tftpdnld  (this command will start the download of IOS from TFTP server)

Sharing Folder between Linux/UNIX systems using NFS

1. Create the folder which we want to share

mkdir /nfs1
chmod 666 /nfs1

2. Share the folder by entering its details in /etc/exports file. In the /etc/exports file, enter the following:

/nfs1       192.168.1.60(rw) [This means this folder can be accessed by 192.168.1.60 in read-write mode]
/nfs2        172.30.10.0/24

3. Start service

service nfs start
ckconfig nfs on

4. Export the file (publishing):

exportfs –v
note: if we add more folder then we can update the exports using exportfs –a

5. Done!!!

How to access these shared folders from the remote 192.168.1.60 system
1. Create a corresponding directory anywhere say nfs1

mkdir /nfs1

2. Mount the remote shared directory (192.168.1.50) to that this directory

mount –t nfs 192.168.1.50:/nfs1 /nfs1

3. Use the “df –h” or “mount” command to confirm it and we are done!!!

Additional configurations
1. Allow client/remote 'root' user the ability to write to /nfs1 export

/etc/exports: (rw,no_root_squash)

2. Setup mount points so that they're available upon reboot

Edit /etc/fstab
192.168.1.50:/nfs1      /nfs1                   nfs     defaults  0 0
note : Unmount and confirm that NFS mount points will be available when the client system changes runlevels (reboots, starts, etc.) - 'mount –a'

3.  showmount -a 192.168.1.50 - shows mounts on this system (connected NFS clients)

How to see and change default MTU in Windows

Open command prompt and type:

netsh interface ipv4 show subinterfaces

and hit Enter. We will get a list of all your network adapters installed on your PC. The MTU value is listed on the left



In command prompt, type the following to ping with an MTU size

ping google.com -f -l 1472

The -f marks packets that should not be fragmented in the ping. -l 1472 sets the size of the packet.



If we get successful replies, then your current MTU is fine for your connection. If we receive error messages like in the above image, then your packets are getting fragmented.

Try to find out successful value. When you find a successful value, you can then set a new MTU limit with this value.You will need to add IP/ICMP overheads (usually 28), so if 1462 is successful, then 1490 is your MTU limit.

To set new limit, in a command prompt use the following command:

netsh interface ipv4 set subinterface "Realtek" mtu=1490 store=persistent

DHCP installation and Configuration on RHEL5/CentOS

1. Install dhcp server

yum –y install dhcp

2. Copy the sample configuration file to /etc

cp -v /usr/share/doc/dhcp-3.0.5/dhcpd.conf.sample /etc/dhcpd.conf

3. Edit the dhcp configuration file /etc/dhcpd.conf as our network details. Also  do the following

#       range dynamic-bootp 192.168.0.128 192.168.0.254; (comment this line and add as below)
        range 192.168.1.150 192.168.1.200;
note: If we dont want specific ip assignments for the hosts (reservation), comment that lines.

4. Start dhcp server

service dhcpd start
chkconfig dhcpd on

5. If we want to configure reservations for a system do as following in the /etc/dhcpd.conf file

host xp1 {
         hardware ethernet 00:0C:29:0C:55:83;
         fixed-address 192.168.1.170;
}
note : Optional 'option-*' are supported between host { } block

6. Restart the service to make the changes to effect

service dhcpd restart

7. Done!!

Notes:
1. On client system /var/lib/dhclient/dhclient-eth0.leases file contains dhcp lease information. On server /var/lib/dhcpd/dhcpd.leases contains the lease information for all clients.
2. NTP details can be given outside the subnet options to make globally available. For more information use ‘man dhcpd.conf’ command.

Installing and configuring TFTP server in Linux (RHEL5 & Centos)

1. Install tftp server using the following command

yum -y install tftp-server

2. Open  /etc/xinetd.d/tftp file using any text editor and make 

disable                 = no

3. Start xinetd server (because tftpd is sub service of that xinetd)

service xinetd start - to start XINETD

4.  Check whether the tftp port 69 using the following command

netstat -nulp | grep 69

5. If selinux is not disabled by default, use the following command to make it disable for the tftpd service

setsebool -P tftpd_disable_trans=1 - disables SELinux for TFTPD
service xinetd restart

6. Installation of tftp server create a directory called /tftpboot where files are stored (tftp root). we must create a
blank file using touch and change permission to 666 using chmod to make it writable

touch r1-config
chmod 666 r1-config

7. Now from cisco router we can use the copy command

R1#copy run tftp://192.168.1.20/r1-config