Section: Network and Telecommunications
Explanation/Reference:
Normal outbound traffic has an internal source IP address and an external destination IP address.
Traffic with an internal source IP address should only come from an internal interface. Such packets coming from an external interface should be dropped.
Packets with the source-routing option enabled usually indicates a network intrusion attempt.
Router information exchange protocols like RIP and OSPF should be dropped to avoid having internal routing equipment being reconfigured by external agents.
Source: STREBE, Matthew and PERKINS, Charles, Firewalls 24seven, Sybex 2000, Chapter 10: The Perfect Firewall.

Explanation/Reference:
The Data Link layer provides data transport across a physical link. It handles physical addressing, network topology, line discipline, error notification, orderly delivery of frames, and optional flow control.
Source: ROTHKE, Ben, CISSP CBK Review presentation on domain 2, August 1999.

Explanation/Reference:
More and more organizations are setting up their own internal PKIs. When these independent PKIs need to interconnect to allow for secure communication to take place (either between departments or different companies), there must be a way for the two root CAs to trust each other.
These two CAs do not have a CA above them they can both trust, so they must carry out cross certification. A cross certification is the process undertaken by CAs to establish a trust relationship in which they rely upon each other's digital certificates and public keys as if they had issued them themselves.
When this is set up, a CA for one company can validate digital certificates from the other company and vice versa.
Reference(s) used for this question:
For more information and illustration on Cross certification: http://www.microsoft.com/technet/prodtechnol/ windowsserver2003/technologies/security/ws03qswp.mspx http://www.entrust.com/resources/pdf/ cross_certification.pdf
also see:
Shon Harris, CISSP All in one book, 4th Edition, Page 727
and
RFC 2459: Internet X.509 Public Key Infrastructure Certificate and CRL Profile; FORD, Warwick & BAUM, Michael S., Secure Electronic Commerce: Building the Infrastructure for Digital Signatures and Encryption (2nd Edition), 2000, Prentice Hall PTR, Page 254.

Two-factor is considered more secure than any single authentication type.

Explanation/Reference:
Personnel cause more security issues than hacker attacks, outside espionage, or equipment failure.
The following answers are incorrect because:
Outside espionage is incorrect as it is not the best answer.
Hackers is also incorrect as it is not the best answer.
Equipment failure is also incorrect as it is not the best answer.
Reference : Shon Harris AIO v3 , Chapter-3: Security Management Practices , Page : 56