Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Searchable, convenient, complete TCP/IP information.
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  TCP/IP Routing Protocols (Gateway Protocols)
                9  TCP/IP Exterior Gateway/Routing Protocols (BGP and EGP)
                     9  TCP/IP Border Gateway Protocol (BGP/BGP-4)
                          9  BGP Fundamentals and General Operation

Previous Topic/Section
BGP Overview, History, Standards and Versions
Previous Page
Pages in Current Topic/Section
1
2
Next Page
BGP Autonomous System Types, Traffic Flows and Routing Policies
Next Topic/Section

BGP Topology, Speakers, Border Routers and Neighbor Relationships (Internal and External Peers)
(Page 2 of 2)

BGP Internal and External Peers

Most BGP speakers will be connected to more than one other speaker. This provides both greater efficiency in the form of more direct paths to different networks, and also redundancy to allow the internetwork to cope with either device or connection failures. It is possible (and in many cases, likely) for a BGP speaker to have neighbor relationships with other BGP speakers both within its own AS and outside its AS. A neighbor within the AS is called an internal peer, while a neighbor outside the AS is an external peer. BGP between internal peers is sometimes called Internal BGP (IBGP) while use of the protocol between external peers is External BGP (EBGP). The two are similar, but differ in certain areas, especially path attributes and route selection. You can see an example of BGP topology and the designation of internal and external peers in Figure 191.


Figure 191: BGP Example Topology and Designations

This diagram is a variation on Figure 171 that shows the names used by BGP to refer to different types of routers and autonomous systems. Internal routers are shown in blue while border routers are red. BGP speakers that communicate within an AS are internal peers, while those that communicate between ASes are external peers. This highly simplified internetwork shows two stub ASes, both of which only connect to the multihomed AS #2.

 


Key Concept: Each router configured to use BGP is called a BGP speaker; these devices exchange route information using the BGP messaging system. Routers that only connect to other routers in the same autonomous system are called internal routers, while those that connect to other ASes are border routers. Neighboring BGP speakers in the same AS are called internal peers, while those in different ASes are external peers.


A peer connection between BGP speakers can be either a direct link using some form of layer two technology, or an indirect link using TCP. This allows the BGP speakers to establish BGP sessions and then exchange routing information, using the messaging system we will see later in this section. Of course, it also is the means by which actual “end user” traffic moves between autonomous systems. External peers are normally connected directly, while internal peers are often linked indirectly.

In the next topic we will see that the method in which ASes are connected has an important impact on the overall function of the internetwork and how traffic is carried on it.


Previous Topic/Section
BGP Overview, History, Standards and Versions
Previous Page
Pages in Current Topic/Section
1
2
Next Page
BGP Autonomous System Types, Traffic Flows and Routing Policies
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.