IPV4 vs IPV6

As a network engineer its very difficult to predict the probable time when all the internet traffic will migrate to Internet protocol version 6(IPV6) . IPV6 offers more advantages than IPV4 in terms of IP address offered, processing delay at each node and host of various features which were not possible in IPV4. But its any ones wild guess to pinpoint a cut off date when all the corporate and home users will migrate to devices supporting IPV6. In the mean time network devices manufactures support IPV4, till end customers replace their network devices supporting full fledged IPV6 features.


The main motive behind introducing new version is to primarily increase the unique address range from 32 bit (i.e. 255:255:255:255 can accommodate up to 4,294,967,296 unique addresses ) to 128 bit (i.e. 255:255:255:255:255:255:255:255:255:255:255:255:255:255:255:255 which can accommodate 2 power 128 unique addresses) thereby provides a opportunity to assign unique address for each Network devices available on the planet for many more years to come.

The next significant advantage of IPV6 over IPV4 is simpler packet header of fixed length with out any check sum or options fields which reduces the delay for each network node (i.e Routers, Gateway devices, etc.) to process the packet. Thus the processing overload for verifying and recalculating check sum and searching for variable options field were completely avoided. Since each devices can be assigned an unique address NAT operations in routers and gateway devices is not required. Fragmentation and Options were moved to extension header to increase routing speed indicated by next header field.

IPSec Protocol based encryption is mandatory in IPV6 to enhance security, which is optional in IPV4. Newer technologies like multi-casting, video streaming, traffic management can be supported and made operational easily using IPV6.

The cost required to migrate all the network devices from IPV4 to IPV6 will be difficult to estimate unless we get a clear picture of patronage from corporate and individual customers. Many government and multinational organizations were slowly migrating to IPV6, to experiment and utilize the advantages of real time deployment benefits in congested and overcrowded Network traffic. Chinese government has taken a proactive step to use IPV6 for all network traffic for the upcoming Beijing Olympics in 2008, which would provide a test bed for testing robustness and security of IPV6.

L2TP Handshaking Sequence for Tunnel Setup (Layer 2 Tunneling Protocol)

Layer 2 tunneling protocol is used mostly to carry(tunnel) PPP packets(L2 layer) over IP Networks, as UDP payload destined to port number 1701. L2TP works by peer to peer communication principles which is different from master slave scenario. Any one peer can intiate the tunnel by requesting the other peer to assign a unique tunnel id and session id for establishing a dedicated tunnel before exchanging data packets (for simplicity we call LNS as server which responds to request & LAC as client which initiates request).

L2TP tunnel initiation between two peers can be established by the following four methods based on tunnel initiation: voluntary tunnel, compulsory tunnel — incoming call, compulsory tunnel — remote dial and L2TP multi-hop connection

In the voluntary tunnel model, a tunnel is created by the user, typically by the use of an L2TP enabled client which is called the LAC client. The user will send L2TP packets to the Internet Service Provider (ISP) which will forward them on to the LNS. The ISP does not need to support L2TP, it only forwards the L2TP packets between LAC and LNS. The LAC client acts as an L2TP tunnel initiator which effectively resides on the same system as the remote client. The tunnel extends across the entire PPP session from the L2TP client to the LNS.

In the compulsory tunnel model-incoming call, a tunnel is created between ISP LAC and the LNS home gateway. The company may provide the remote user with a Virtual Private Network (VPN) login account from which he can access the corporate server. As a result the user will send PPP packets to the ISP (LAC) which will encapsulate them in L2TP and tunnel them to the LNS. In the compulsory tunneling cases, the ISP must be L2TP capable. In this model the tunnel only extends across the segment of the PPP session between the ISP and the LNS.

In the compulsory tunnel model-remote dial the home gateway (LNS) initiates a tunnel to an ISP (LAC) (outgoing call) and instructs the ISP to place a local call to the PPP enabled client which is the remote user. This model is intended for cases where the remote PPP Answer Client has a permanently established phone number with an ISP. This model is expected to be used when a company with established presence on the Internet needs to establish a connection to a remote office that requires a dial-up link. In this model the tunnel only extends across the segment of the PPP session between the LNS and the ISP.

An L2TP Multi-hop connection is a way of redirecting L2TP traffic on behalf of client LACs and LNSs. A Multi-hop connection is established using an L2TP Multi-hop gateway. A tunnel is established from a client LAC to the L2TP Multi-hop gateway and then another tunnel is established between the L2TP Multi-hop gateway and a target LNS. L2TP traffic between client LAC and LNS is redirected to each other through the gateway.

During tunnel initiation numerous control packets were exchanged between two peers for handshaking and to assign tunnel and session ID between two peers, which were later used to uniquely represent the tunnel for exchanging data.The handshaking methods for assigning and negotiating tunnel and session id for a voluntary tunnel were explained by the below picture which was hosted by me in wikipedia.