Summary of "eBGP vs iBGP - What's the difference?"
eBGP vs iBGP - What’s the difference?
The video titled “eBGP vs iBGP - What’s the difference?” by Lazarus at telecomTech provides a clear explanation of the technological concepts and operational differences between external BGP (eBGP) and internal BGP (iBGP), both manifestations of the Border Gateway Protocol used for Internet routing.
Key Technological Concepts and Features
BGP Overview
BGP subdivides the Internet into Autonomous Systems (AS), each identified by a unique AS number and managed by organizations like ISPs or enterprises. BGP routers within and between these ASes exchange routing information.
eBGP vs iBGP Definition
- eBGP: BGP peering between routers in different ASes.
- iBGP: BGP peering between routers within the same AS.
Both use the same protocol but differ in behavior and configuration.
Configuration Differences (Cisco example)
- eBGP: The local AS and neighbor AS numbers differ in the configuration.
- iBGP: The local AS and neighbor AS numbers are the same.
Implementation Rules
- iBGP requires a full mesh of BGP peerings within the AS (every iBGP router peers with every other).
- eBGP does not require full mesh and typically peers directly connected routers.
- iBGP peers can be multiple hops apart if routing is provided by an IGP or static routes.
Route Handling Differences
-
Administrative Distance (AD):
- eBGP routes have a default AD of 20 (more trusted).
- iBGP routes have AD of 200 (less trusted).
-
Next Hop Attribute:
- eBGP updates change the next hop to the IP of the interface facing the eBGP peer.
- iBGP updates preserve the original next hop IP.
-
AS Path Attribute:
- eBGP prepends the local AS number to the AS Path when advertising routes.
- iBGP does not modify the AS Path when advertising routes.
Role in Network Hierarchy
- eBGP manages routing between different ASes (inter-AS routing).
- iBGP manages routing within the same AS (intra-AS routing).
Prerequisite
Before configuring iBGP, routing within the AS must be fully established using an Interior Gateway Protocol (IGP) such as OSPF or EIGRP. This is necessary because iBGP does not handle internal routing itself.
Summary Points
- eBGP and iBGP are the same protocol but differ in peering type and behavior.
- eBGP connects routers across AS boundaries; iBGP connects routers within the same AS.
- Different configuration and operational rules apply to each for scalability and routing correctness.
- Differences exist in route advertisement attributes such as next hop, AS path, and administrative distance.
- Internal routing protocols (IGPs) are required to support iBGP operations inside an AS.
Tutorial/Guide Elements
- Explanation of BGP fundamentals with diagrams illustrating router peerings.
- Cisco router configuration examples highlighting AS number settings for eBGP and iBGP.
- Detailed comparison of route attributes and handling.
- Practical advice on implementation best practices (e.g., full mesh for iBGP, direct connection for eBGP).
- Clarification on the role of IGPs alongside BGP.
Main Speaker/Source
- Lazarus, host of telecomTech, specializing in clear explanations of telecom and networking technologies.
Category
Technology
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