Which of the following are suitable protocols for securing VPN connections at the lower layers of the OSI
model?

A.
S/MIME and SSH

B.
TLS and SSL

C.
IPsec and L2TP

D.
PKCS#10 and X.509

Explanation:
Layer 2 Tunneling Protocol (L2TP) is a combination of PPTP and the earlier Layer 2 Forwarding Protocol (L2F)
that works at the Data Link Layer like PPTP. It has become an accepted tunneling standard for VPNs.
IPSec operates at the Network Layer and it enables multiple and simultaneous tunnels. IPSec has the
functionality to encrypt and authenticate IP data. It is built into the new IPv6 standard, and is used as an add-on
to the current IPv4. While PPTP and L2TP are aimed more at dial-up VPNs, IPSec focuses more on networkto-network connectivity.
Incorrect Answers:
A: S/MIME and SSH run in the application layer (layer 7) of the OSI model. This is the highest level, not a lower
level.
B: TLS runs in layer 6 of the OSI model and SSL runs in layer 4. L2TP and IPSEC run in layers 2 and 3
respectively.
D: PKCS#10 and X.509 alone do not provide VPN connections; they are used by other protocols.