Telnet and Secure Shell (SSH)

Telnet

• Legacy client & server terminal
  • Old stuff that is not replaced by new stuff
  • A terminal is a live action interface
  • SDN is a new of do things
• TCP port 23
  • 21 - FTP
  • 22 - SSH
  • 23 - Telnet
  • 25 - SMTP
• Widely supported
• Susceptible to eavesdropping and hijacking
• Only available option on some devices
  • We can Isolate the device and just put it in a different VLAN
• Isolate traffic to Out-of-Bond (OOB) management network
  • Dedicated network that does not share stuff with the users
  • Dedicated Ethernet Management Interface
  • The only way to get on that network is coming in from the firewall and authenticate.

Secure Shell

• Preferred CLI interface for remote administration
• TCP port 22
• Supports file transfer - SCP
• Public Key authentication optional
• Can restrict access by IP address, time of day, group membership
• Might require dedicated application
• Encrypt / Auth / Int

• When the client connects to a server on port 22
  • We do the 3 way handshake
  • Negotiate protocols
  • Here is a public key, should you accept it?
  • Key Pair is typically generated using RSA / DSA
  • 2048 - 4096
  • The dilema is when we get that public key, how do we know that that public key really came from that device
    • The public key can be saved
    • We have mutual authentication