The LD50 of nicotine is 50 mg/kg for rats and 3 mg/kg for mice. 0.5-1.0 mg/kg can be a lethal dosage for adult humans, and 0.1 mg/kg for children.
IPSec is a suite of protocols that provide security services at IP layer of TCP/IP stack i.e. Network Layer in OSI model. As Andy Lemke mentioned, IPSec suite comprises of two protocols to offer security to. 1. AH - Authentication Header Protocol.(Protocol no: 51) 2. ESP - Encapsulation of security payload Protocol.
IPSec transport mode (encrypting an IP GRE tunnel) is a commonly deployed option because it provides all the advantages of using IP GRE, such as IP Multicast protocol support (and, thus, also the support of routing protocols that utilize IP Multicast) and multiprotocol support.