## Monday, May 31, 2010

### What is Inter Packet Gap or Inter Frame Gap?

Let's assume if a Gigi port which could transfer raw data up to 125,000,000 bytes per second with minimum frame size of 64 bytes. Device must need some time to process one packet after another. The difference of time to process from one packet to another is known as inter-frame or inter-packet gap. The minimum inter frame gap period is 96 bits or 12 bytes which amounts to 96 nano seconds + 7 byte of preamble and 1 byte of delimiter consequence 84 bytes.

## Thursday, May 27, 2010

### Diffie-Hellman(DH) Shared Key Exchange Mechanism

Diffie-Hellman is cryptography protocol, which allows two users to exchange the key over the public cloud. Mainly VPN uses Diffie-Hellman algorithms to provide reliable and trusted method of key exchanges. The algorithm was being invented by Whitefiled Diffie and Martin Hellman in 1976. During DH exchange both users must agree on two non secret numbers which could be available publically or in the form of any certificate. After this agreement, users exchange their keys and come to know that their and remote user keys are same. After bona fied to each other, they start exchange their data.
In this post, I will explain how the keys values are calculated. First we need to define two public keys which are available through any certificate or via any other method to both users. Let’s assume n and g are public keys for user1 and user2. Value of g should be small and n(take big values) should be prime number.
Both users are having same keys initially.
n=997
g=2
Next step is to use the private keys and compute the value which should be given to remote user.
Private key for user1 is 3 and for user2 is 5.

Calculate the public key value which will be transmitted to remote user. Formula for calculating Public Value for User1 will be given below:-
Public Value:- g^(private key of user1) mod n
Public Value:- 2^3 mod 997
Public Value:- 8 mod 997
Public Value:- 8

Formula for calculating Public Value for User2 will be given below:-
Public Value:- g^(private key of user2) mod n
Public Value:- 2^5 mod 997
Public Value:- 32 mod 997
Public Value:- 32

Now both users will exchange their public values to each other and on the basics of receiving public values user will calculate the secret key.
User1 is receiving 32 from user2 and user2 is receiving 8 from user1

User1 will calculate it’s shared key by using given formula:-
User1 Shared Key:- (Received Public Key From User2)^(user1 private key) mod n
User1 Shared Key:-32^3 mod 997
User1 Shared Key:-32768 mod 997
User1 Shared Key:- 864

User2 will calculate it’s shared key by using given formula:-
User2 Shared Key:- (Received Public Key From User1)^(user2 private key) mod n
User2 Shared Key:-8^5 mod 997
User2 Shared Key:-32768 mod 997
User2 Shared Key:- 864

User1 and User2 are having same shared keys which is 864

## Tuesday, May 18, 2010

### Wimax Interfaces Naming Convention

IP network interfaces are called as core interfaces,access interfaces or PE-CE interfaces. But in WIMAX, interfaces are named as depicted belows:-
1. R1 Interface:- This is actual wireless interface which connects Mobile Subscriber to BS(Base Station).
2. R2 Interface:- This is the logical interface with CSN(Core Service Network). In case of Mobile IP.
3. R3 Interface:- Interface between ASN(Access Service Network) and CSN(Core Service Network).All the radius messages are exchanged on this interface.
4. R4 Interface:- This is the logical interface between ASN-Gty(Access Service Network). This interface is used during handovers in romaing.

5. R5 Interface:- This is logical interface between Home CSN(Core Service Network). This is used during roaming scenarios.
6. R6 Interface:- This is the physical or logical interface between BS(Base Station) and ASN-Gty.
7. R7 Interface:- This is logical/physical interface between decision point and enforcement point. Both are the parts of ASN-Gty.
8. R8 Interface:- This is logical interface between BS(Base Station). This is used during handovers from one BS to another.

## Sunday, May 16, 2010

Twitter is becoming a daily life part and before the start of any new work, we would like to post updates on twitter. Twitter is growing incredibly because it's easy to use and secure. Today after noon, when I was analyzing some of my yesterday pcap files and I was astonished to see that twitter is sending clear text password during change in profile setting. This could be a high alert flaw because without using keyword logger, I am loosing my password identity. On the same lan twitter hack could expose lot of username and passwords. I had captured the logs where in password field is colored with black and I could see it with my naked eyes because
it is in clear text format which is explicitly depicting that Twitter team is not using any encryption method during setting or profile updates.
Image 1

Image 2

## Wednesday, May 12, 2010

### Wimax Architecture

Wimax is fully ip network which gives the last mile users to access internet at high speed. Wimax architecture consists of the following components:-
1. MS(Mobile Subscriber) or SS(Subscriber Station)
2. ASN (Access Service Network)
3. CSN (Core or connectivity Service Network)
MS or SS are used by the users to connect the VPN or Internet by using air interface. All the MS or SS connects to the BS(Base Station) and BS further connects to the ASN-Gty.
ASN network consists of Base Stations and ASN-Gty(Access Service Network Gateway). BS are responsible for providing air interface to mobile subscribers to connect VPN or Internet. Apart from this BS manages the subscribers QOS policy enforcements, traffic classification, session managements and handovers during roaming.

ASN-Gty works as LNS(Layer 2 Network Server) server which aggregates all the layer 2 traffic and provides the connectivity to internet. A part from this it manages QOS profiles, keys management, radius client, mobility tunnels with base stations for roaming users. Allocates profile as Simple and Mobile ip communication for SS or MS and becomes foreign agent for them.

CNS consists of AAA, HA, VHR, OSS. It connects to the internet gateway to route the traffic in case of data network. If MS looks for voip calls in that case it also provides the connectivity to PSTN network.

## Thursday, May 6, 2010

### Cisco CCNA Service Provider

The Cisco CCNA Service Provider (SP) Operations certification and the written exam for the CCIE Service Provider (SP) Operations certification are now available.
The Cisco CCNA SP Operations certification targets entry-level students with a foundation of network operations skills in SP IP NGN environments required of associate-level operations personnel. Both the Supporting Cisco Service Provider IP NGN Operations (SSPO) course and required # 640-760 exam are now available. Interested students should access the CCNA SP Operations home page for more information.

This exam code is 640-760 SSPO (Supporting Cisco Service Provider IP NGN Operations).
Sources:- Cisco.com

## Tuesday, May 4, 2010

### OSPF Sham Link In Different Area

One of my reader asked a question,"Normally customers require sham link to prefer back door link in case of MPLS VPN environment, when customer run same area. But if the customer is using different area, how the back door link work."
If we read RFC 2328 which is clearly states that to make communication possible between two areas,OSPF must have area 0 connectivity. In this type of topology, the backdoor will never work.
If someone is having any different thought, please share it.