Which two options best describe the purpose of session ID and cookie field in a L2TPv3 packet?

Question

Options

• AThe session ID is a 32-bit locally significant field used to identify the call on the destination or egress
• BThe cookie is a variable length(with a maximum of eight bytes),word-aligned optional field. The control
• CThe cookie is a 32-bit locally significant field used to identify the call on the destination or egress tunnel
• DThe session ID is a variable length(with a maximum of eight bytes),word-aligned optional field.

• A
  78% (14)
• C
  17% (3)
• D
  6% (1)

Explanation

The 32-bit nonzero session ID carried in the data message header is used to associate incoming data messages with a particular local attachment circuit. Note that one L2TPv3 session corresponds to one pseudowire. Following the session ID is an optional variable length random cookie value (maximum 64 bits). This cookie value can be used in addition to the session ID and adds an extra level of assurance that the incoming data messages are correctly associated with the local attachment circuit. Furthermore, a randomly chosen cookie provides protection against blind insertion attacks. That is, an attacker would find it very difficult, if not impossible, to insert packets into a data stream (pseudowire) if the attacker is unable to sniff packets transiting the network between peer LCCEs. This is because of the difficulty of guessing the correct cookie value (0 to 264 if the cookie is 64 bits in length).

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