Exterior gateway protocol

An overview of Exterior Gateway Protocol, its origins, inner workings, and its place in the world of proxy servers.

The History and Origins of Exterior Gateway Protocol

Exterior Gateway Protocol (EGP), as we know it today, first emerged in the late 20th century. With the rapid growth of the internet in the 1980s, there emerged a need for a standardized method of exchanging routing table information between autonomous systems (AS), which are networks managed by a single enterprise.

The first mention of EGP was in 1982, in a document titled “EGP – Exterior Gateway Protocol,” published as RFC 827. RFCs, or Requests for Comments, are a series of memos that discuss many aspects of computer networking, including protocols, procedures, programs, and concepts. This RFC was written by Eric C. Rosen from Bolt Beranek and Newman Inc., which played a significant role in the development of the internet.

Expanding on the Topic: Exterior Gateway Protocol

EGP is a distance-vector protocol used to exchange routing information between different autonomous systems on the internet. An Autonomous System (AS) is essentially a network or a collection of networks under the control of one entity, such as an ISP or a large corporate organization.

EGP was created for use in an environment where each gateway (router) is assumed to have a direct connection to each AS. Each EGP-enabled router communicates with its peers to exchange network reachability information, enabling routers to make informed decisions about the best path for forwarding packets.

However, EGP is not designed to determine the best path for data transmission based on metrics like distance or cost. Instead, it simply propagates routing information and depends on interior gateway protocols (IGP), such as RIP or OSPF, to select the optimal path.

The Internal Structure and Working of the Exterior Gateway Protocol

EGP operates on a simple set of commands and messages exchanged between routers. The protocol defines five types of messages: Hello/I-Heard-You (I-H-U), Request, Update, Response, and Poll.

Hello and I-H-U messages are used to establish and maintain neighbor relationships between routers. The Request and Update messages are used to request and send routing information, while Response and Poll messages are utilized to acknowledge receipt of updates and to solicit updates.

EGP works by establishing a neighbor relationship between a core gateway (router) and an edge gateway. Once this relationship is formed, the edge gateway sends an EGP Poll message to the core gateway, which responds with an EGP Update message that contains a list of networks that can be reached via the core gateway. The edge gateway can then update its routing table accordingly.

Key Features of the Exterior Gateway Protocol

Key features of EGP include:

• Neighbor Acquisition: This process involves the establishment and maintenance of neighbor relationships between routers.
• Reliable Transport: EGP uses the User Datagram Protocol (UDP) for transmission and includes mechanisms for reliable message exchange.
• Network Reachability Information Exchange: EGP provides the ability to exchange information about network reachability between routers in different autonomous systems.
• Polling Mechanism: EGP uses a polling mechanism, which is a form of asking for routing updates, to exchange routing information.

Types of Exterior Gateway Protocols

Over time, various versions of exterior gateway protocols have emerged to meet different networking requirements:

Ways to Use EGP and Associated Challenges

EGP is primarily used to connect an autonomous system with an internet backbone. However, this protocol is not without challenges:

• Limited Routing Metrics: EGP doesn’t consider the path’s metrics like cost, bandwidth, or congestion while deciding the best route for packet forwarding.
• No Loop Prevention Mechanism: EGP lacks any inherent loop prevention mechanism, making it vulnerable to routing loops.
• Scalability Issues: As the number of autonomous systems grew on the internet, EGP faced scalability issues.

These problems are solved by using advanced protocols like BGP. BGP offers loop prevention mechanisms, considers path attributes for route selection, and supports CIDR (Classless Inter-Domain Routing), which allows for more efficient use of IP address space and better scalability.

Comparison with Similar Terms

Perspectives and Future Technologies Related to EGP

Though EGP has been largely superseded by BGP, the principles behind its creation continue to influence internet routing. Future enhancements in exterior gateway protocols may include more robust security features, better support for IPv6, and improvements in policy-based routing.

Proxy Servers and Exterior Gateway Protocol

While proxy servers themselves do not directly use EGP or other routing protocols, their functionality is closely tied to the efficient operation of these protocols. Proxy servers, like those offered by OneProxy, serve as intermediaries between clients and the wider internet. They rely on the proper functioning of internet routing protocols, including BGP, to ensure that client requests are sent to the right servers and responses returned in a timely manner.

In some cases, proxy servers may be part of networks that utilize BGP or other EGPs. For example, a large proxy server provider might use BGP to manage routing between its network and other ISPs.

Related Links

For more detailed information about Exterior Gateway Protocol, you may visit the following resources:

• RFC 827 – EGP specification
• RFC 4271 – BGP-4 specification
• Cisco’s Overview of Routing Protocols

Whether you’re interested in the historical foundations of internet routing or looking to understand the mechanics behind your favorite proxy service, understanding Exterior Gateway Protocol is a valuable part of the journey.