VPN (Virtual Private network)

Basic Notes about VPN

A VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together.It works by encapsulating data for one network inside of an ordinary IP packet and transporting that packet to another network. When the packet arrives at the destination network, it is unwrapped and delivered to the appropriate host on the destination network. By encapsulating the data using cryptographic techniques, the data is protected from tampering and snooping while it is transported over the public network.

Through VPN you can access your private network in remote location over Internet without compromising the security. VPNs allow employees to securely access their company's Intranet while travelling outside the office. Similarly, VPNs securely connect different branch offices together via internet without dedicated lease line and its much cheaper than lease lines. VPNs also use strong encryption to provide privacy and strong authentication to guarantee identity, so they are more secure than traditional networks.By using a VPN, businesses ensure security,That means even if the data is hacked while sending through VPN, hacker can't read data as its in encrypted format.

Different VPNs used 

VPNs can be either remote-access (connecting an individual computer to a network) or site-to-site (connecting two networks together). In a corporate setting, remote-access VPNs allow employees to access their company's Intranet from home or while travelling outside the office, and site-to-site VPNs allow employees in different geographically location to share one network.

One interesting thing to note about VPNs is that there are no standards about how to set them up. If you're establishing your own VPN, though, it's up to you to decide which protocols and components to use and to understand how they work together.

Five basic components of VPNs:

VPN Gateways:
A device used to connect an entire network to the VPN
VPN Client Software: 
Software for individual PCs that allow them to connect to the VPN
Authentication Servers: 
Systems such as certificate authorities and RADIUS servers that guarantee the identity of VPN Gateways and Clients
Manage Servers: 
Systems that provide control, monitoring, alerting and reporting on the VPN
Physical Transport: 
Any IP or Internet connection

Advantages of VPN

Security -- The VPN should protect data while it's travelling on the public network. If intruders attempt to capture the data, they should be unable to read or use it.
Reliability -- Employees and remote offices should be able to connect to the VPN with no trouble at any time (unless hours are restricted), and the VPN should provide the same quality of connection for each user even when it is handling its maximum number of simultaneous connections.
Scalability -- As a business grows, it should be able to extend its VPN services to handle that growth without replacing the VPN technology altogether.

LSA Types in OSPF

LSA Types in OSPF

• Router LSA (Type 1) – Contains a list of all links local to the router, and the status and “cost” of those links. Type 1 LSAs are generated by all routers in OSPF, and are flooded to all other routers within the local area. 

• Network LSA (Type 2) – Generated by all Designated Routers in OSPF, and contains a list of all routers attached to the Designated Router. 

• Network Summary LSA (Type 3) – Generated by all ABRs in OSPF, and contains a list of all destination networks within an area. Type 3 LSAs are sent between areas to allow inter-area communication to occur. 

• ASBR Summary LSA (Type 4) – Generated by ABRs in OSPF, and contains a route to any ASBRs in the OSPF system. Type 4 LSAs are sent from an ABR into its local area, so that Internal routers know how to exit the Autonomous System. 

• External LSA (Type 5) – Generated by ASBRs in OSPF, and contain routes to destination networks outside the local Autonomous System. Type 5 LSAs can also take the form of a default route to all networks outside the local AS. Type 5 LSAs are flooded to all areas in the OSPF system. 

• Type 7 NSSA (Not-So-Stubby-Area) - Used in stub areas in place of a type 5 LSA 

NOTE : LSA types 1 and 2 are found in all areas, and are never flooded outside of an area.

Understand the significance of administrative distance and metrics

Administrative distance and metrics are two important factors when it comes to which routing protocols.

Being knowledgeable about these two Values can make all the difference in network performance, reliability, and path selection.

If you haven’t seen or heard about these two value and you have completed the course of CCNA means that you have missed something important in the class.

Let me give you an example.

When you enter the command “Show ip route” you will see the following output. Look at the two values in the bracket.

R    10.0.0.0/8 [120/1] via 1.1.1.1, 00:00:15, FastEthernet0/0

Here, 120 represent the Ad Value and 1 represents the metric. The R at the starting represents the route learned via RIP. So the Ad value of RIP is 120 and the metric it took to reach the network is 1.

You can also get the more details about the specific network by using the command show ip route followed by the network you want to know more.

Here’s an example,

***************************************************************************************************************************************************

R2#sh ip route 10.0.0.0

Routing entry for 10.0.0.0/8

  Known via "rip", distance 120, metric 1

  Redistributing via rip

  Last update from 1.1.1.1 on FastEthernet0/0, 00:00:09 ago

  Routing Descriptor Blocks:

  * 1.1.1.1, from 1.1.1.1, 00:00:09 ago, via FastEthernet0/0

      Route metric is 1, traffic share count is 1

******************************************************************************************************************************************************

ADMINISTRATIVE DISTANCE:  It is value used by Cisco routers to select the best path between source and destination when multiple protocols are used.

E.g. An OSPF route with an administrative distance of 110 will be chosen over a RIP route with an administrative distance of 120.

Protocol	Administrative Distance
Directly Connected Route	0
Static route out of an interface	1*
Static route to next-hop ip address	1
EIGRP summary Route	5
External BGP	20
Internal EIGRP	90
IGRP	100
OSPF	110
IS-IS	115
RIP	120
EGP	140
ODR	160
External EIGRP	170
Internal BGP	200
DHCP- learned	254
Unknown	255

·         A route with the value of AD 255 will not be installed in routing table because the router will not trust that route.

·         Since IOS 12.2, the administrative distance of a static route with an exit interface is 1. Prior to the release of 12.2 it was in fact 0.

* Actual administrative distance is recognized somewhere between 0 and 1. This AD is more trustworthy than 1 but less trustworthy than 0.

Metric:

It is the method or formula used by a protocol to find the best path between source and destination, when more than one path is available for the same destination.

So, a routing protocol uses its metric to find the best path to reach the destination when more than one path is available. The lower the metric the more preferred path that will be installed in the routing table.

Unlike Administrative distance metric is involved in with only one routing protocol. Every routing protocol has its own metric to find the best path.

e.g.  Look at the output of the command of show ip eigrp topology

P 10.55.102.0/24, 1 successors, FD is 6049256
        via 10.220.100.11 (6049256/5537506), Serial3/0
        via 10.55.100.114 (52825700/281610), Serial2/0

In the above output EIGRP has two routes to reach the net 10.55.102.0/24. But only with the route with lower metric will be installed in the routing table.

So the first route i.e. via 10.220.100.11 will be installed in the routing table as it has lower metric. The values in the bracket in the above output says, the first part is the Feasible distance (FD) to the destination and the second part is the advertise distance to the destination (AD). The output in the brackets means (FD/AD).

Different routing protocols calculate their metric in different ways. RIP uses hops, OSPF uses bandwidth, and EIGRP uses a combination of bandwidth, delay, load, and reliability.

For more details mail me at arahim.cisco@gmail.com

CISCO IOS Naming Standerd

Below is Cisco IOS Naming Standard