SSH: SECURE SHELL PROTOCOL

• telnet traffic is sent in a clear text way, so it is not secure.
• It is a client/server protocol that encrypt the traffic in and out through vty ports.
• By default cisco router & switches act as SSH clients.
• To make CISCO router & switches act as SSH servers they must be configured.
• Authentications is required to connect clients.
• This authentication can be username & password or authentication with a AAA server .
• There are 2 versions in SSH
• Version 2 more secure than the Version 1.
• Cisco devices supports both versions.
• Must specify which version u want use.
• Configuring basic SSH Server requires following steps:
• Check IOS support ssh or not.
• Configure a host name (if already config leave it)
• Config a domain name. (if already  config leave  it)
• Config a client authentication method.
• Router or Switch generate RSA keys that will be used to encrypt the session.
• specify the SSH version, if u want to use version 2.
• Disable telnet on the VTY lines.
• Enable SSH on the VTY lines.
• 
  

SECUIRITY

• 3 Modes to access the user mode is:
• CONSOLE
• AUX
• TELNET
• Simple user mode CLI password protection
• line con 0
•   login
•   password cisco
• line vty 0 15
•   login
•   password cisco
• these passwords are stored as clear text in the configuration
• these passwords are encrypted by  service password-encryption command
• service password-encryption
• line console 0
•     password 7 "type pass here"
•    login
• line vty 0 4
•     password 7 "type pass here"
•     login
• after service password-encryption command is added to configuration, all clear text passwords in the running configuration are changed to an encrypted value.
• Untill copy run start , passwords in startup config are not encrypted.
• no service password-encryption command cannot automatically decrypt the encrypted passwords.
• This type encryption is weak, using some public tools can easily decrypt the passwords.

PIM-DM

PIM- Dense Mode:

• used in a situation:
• networks where many multicast clients are tightly spaced together in small networks.

PIM: Protocol Independent Multicast

• PIM is used for router to router communication.
• PIM depend upon the unicast routing protocols for topology information.
• Multicast groups can be either sparse or dense.
• Multicast interfaces are configured as either sparse or dense or both.
• PIMv2 hello message: 30sec
• on PIM enabled interfaces.
• PIMv2 hold time value: 90sec
• PIMv2 uses protocol 103 & reserved multicast address 224.0.0.13
• PIM mode only determine how traffic is send from an interface, not how it recieved.
• DR Router: single router send  IGMP host-query messages to host group membership
• Highest ip number will be DR
• Assert Forwarder: 
• one router will be elected & responsible for forwarding multicast traffic.
• AS election:
• admin distance to the source
• lowest metric to the source
• if tie, highest ip address

IGMP: Internet Group Management Protocol

• IGMP is automatically enabled when PIM enabled.
• IGMP enables the communication between multicast routers and their hosts.
• Multicast routers uses the IGMP to send ip packets to what multicast groups on what interfaces.
• Host Membership query:
• Routers use the queries to discover the presence of multicast group member on a subnet.
• general membership query is sent to the group address 0.0.0.0.
• group specific query is sent to the group address that is required.
• Host Membership Reports:
• Hosts replies to queries.
•