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NAT Behavior Discovery Using Classic STUN (RFC 3489)

Let us introduce the NAT behavior discovery algorithms defined in RFC 3489. To fully understand what's discussed below, we recommend you read the following posts first: 1. NAT Behavioral Requirements, as Defined by the IETF (RFC 4787) - Part 1. Mapping Behavior 2. NAT Behavioral Requirements, as Defined by the IETF (RFC 4787) - Part 2. Filtering Behavior 3. STUN (RFC 3489) vs. STUN (R...

11/04/2013

45,158

Technical Documents

What is DHCP Option 82?

We will look into DHCP Option 82 used in the wireline networks of network operators today. Most of you are probably subscribing to a wireline Internet service provided by one of the network operators such as KT, SK Telecom or LGU+ (Korean Operators). When users subscribe to the Internet service, they pay a monthly fee to their network operator for using the Internet service. So, as a genera...

11/01/2013

54,512

Tech-Blog

Understanding the Detailed Operations of DHCP

Table of Contents I. Introduction II. Procedures for Detecting IP Address Conflicts III. DHCP Offer/ACK Messages: Broadcast or Unicast ? IV. State Transition of DHCP Clients I. Overview Dynamic Host Configuration Protocol (DHCP) has been widely adopted as a protocol for allocating network configuration data, including an IP address, dynamically to...

10/30/2013

84,596

Technical Documents

Understanding the Basic Operations of DHCP

Table of Contents I. Introduction II. IP Address Allocation/Lease Procedure III. IP Address Renewal Procedure IV. IP Address Release Procedure V. Summary VI. Closing Appendix A - Format of DHCP Messages in IP Address Allocation/Lease Procedure Appendix B - Format of DHCP Messages in IP Address Renewal Procedure Appendix C - Format of DHCP Me...

10/23/2013

377,261

Technical Documents

STUN (RFC 3489) vs. STUN (RFC 5389/5780)

What are the differences between NAT types defined in RFC 3489 and RFC 5780? To understand the differences to be explained below, you must be familiar with the Mapping Behavior and Filtering Behavior of a NAT that we covered last time. What is STUN? STUN is a protocol that allows two devices (P2P devices) to discover the presence and types of a NAT between them, and to find out what Exte...

10/21/2013

49,138

Technical Documents

DHCP message format

10/11/2013

20,062

One-Shot Gallery

NAT Behavioral Requirements, as Defined by the IETF (RFC 4787) - Part 3. Deterministic...

NAT Behavioral Requirements, as Defined by the IETF (RFC 4787) Part 1. Mapping Behavior Part 2. Filtering Behavior Part 3. Deterministic Properties This is the last post on RFC 4787. 4. Application Level Gateway For information about Application Level Gateways (ALGs), please click here....

10/10/2013

34,645

Technical Documents

DHCP Security Using a DHCP Proxy Agent

Last time when we introduced a DHCP proxy agent through our previous blog post dated in September 1. 2013, we mentioned that this DHCP proxy agent can offer the benefits of enhanced security. So, we will look into these security-related functions in more detail today. As shown in the figure below, if there is a DHCP proxy agent in a network, all DHCP messages (used in IP address allocation...

10/01/2013

46,223

Tech-Blog

NAT Behavioral Requirements, as Defined by the IETF (RFC 4787) - Part 2. Filtering Beha...

NAT Behavioral Requirements, as Defined by the IETF (RFC 4787) Part 1. Mapping Behavior Part 2. Filtering Behavior Part 3. Deterministic Properties Now that we learned a NAT's mapping behaviors last time, below we will study its filtering behaviors as defined in RFC 4787. For information about the terms used below (Internal En...

09/23/2013

34,708

Technical Documents

NAT Behavioral Requirements, as Defined by the IETF (RFC 4787) - Part 1. Mapping Behavior

NAT Behavioral Requirements, as Defined by the IETF (RFC 4787) Part 1. Mapping Behavior Part 2. Filtering Behavior Part 3. Deterministic Properties Many applications like Skype, online games, etc. are all Peer-to-Peer (P2P) applications based on UDP. When running these applications, two devices communicate with each other without a...

09/12/2013

37,240

Technical Documents

Network Address Translation (NAT) Overview (RFC 3022/2663)

Today, NATs are employed by Korean telecom operators in almost all of their access networks except for wired access networks (FTTH, Ethernet, DSL, etc.). 3G/LTE network: Large Scale NAT (LSN) installed beyond GGSN/P-GW in the 3G/LTE core networks. Also called "Carrier Grade NAT (CGN)". Wi-Fi Hotspot network: NAT implemented in Wi-Fi hotspot AP. Residential network: NAT implemented in su...

09/03/2013

34,474

Technical Documents

Network Address Translation (NAT) Overview (RFC 3022/2663)

09/03/2013

20,588

One-Shot Gallery

What is a DHCP Proxy Agent?

Now that we know what DHCP relay agents are, we will find out another DHCP agent, a DHCP proxy agent today. What a DHCP relay agent does is simply relay broadcast DHCP packets (DHCP Discover/Request) to DHCP server(s) located in other subnets whenever it receives packets from a DHCP client residing in that same subnet. On the other hand, a DHCP proxy agent not only relays the DHCP packets...

09/01/2013

44,119

Tech-Blog

What is a DHCP Relay Agent?

We talked about the basic operations of DHCP in our previous blog post, "What is DHCP?”. Today, we will find out what kind of agent a DHCP relay agent is. Generally, DHCP messages are broadcasted. So, in order for the messages to be exchanged between a DHCP client (PC) and DHCP server, both the client and server have to reside on the same subnet. That is because routers do not fo...

08/01/2013

85,827

Tech-Blog

What is DHCP?

As we need a phone number to make a call to someone, we need an address to communicate with a network host over the Internet. This address is called an "Internet Protocol (IP) address". Generally, IP addresses are dynamically allocated to clients accessing the Internet, through Dynamic Host Configuration Protocol (DHCP), a protocol designed for dynamic allocation of IP addresses, as defined in...

07/01/2013

46,879

Tech-Blog