Advanced Routing Protocols – EIGRP and BGP

Advanced Routing Protocols – EIGRP and BGP

Routing protocols play a crucial role in directing network traffic efficiently. Two advanced routing protocols widely used in large-scale networks are Enhanced Interior Gateway Routing Protocol (EIGRP) and Border Gateway Protocol (BGP).

Enhanced Interior Gateway Routing Protocol (EIGRP)

EIGRP is an advanced routing protocol developed by Cisco Systems. It is designed for use within an autonomous system (AS) and is known for its rapid convergence and low bandwidth usage. EIGRP incorporates features of both distance vector and link-state routing protocols.

Key Concepts:

  • Autonomous System (AS): A collection of IP networks and routers under the control of a single organization, typically using a common routing protocol.
  • EIGRP Neighborship: EIGRP routers establish neighbour relationships to share routing information. These neighbours exchange routing updates to maintain an accurate view of the network.
  • Reliable Transport Protocol (RTP): EIGRP uses RTP for the delivery of EIGRP packets. RTP ensures the reliable and ordered delivery of EIGRP messages between neighbours.
  • Dual (Diffusing Update Algorithm): The algorithm used by EIGRP for calculating the best path to a destination. It considers bandwidth, delay, reliability, and load in its metric calculation.


Enabling EIGRP on interfaces

router eigrp [AS-number]   
network [network-address] [wildcard-mask]

Configuring router ID

router eigrp [AS-number]
eigrp router-id [router-id]

Fine-tuning metrics

  interface [interface-type] [interface-number]
  bandwidth [bandwidth-in-kbps]

Authentication and summarization

  router eigrp [AS-number]
  authentication mode [md5]
  summary-address [summary-address]

AS-number is Autonomous System number


Verifying EIGRP neighbors

  show ip eigrp neighbors

Analyzing topology tables

  show ip eigrp topology

Debugging commands

  debug eigrp packets

Border Gateway Protocol (BGP)

BGP is a path vector protocol widely used for routing between different autonomous systems (AS) on the internet. It places emphasis on policy-based routing, allowing administrators to control the selection of network paths.

Key Concepts

  • BGP Peering: BGP routers form peering sessions to exchange routing information. Peering can be established within the same AS (internal BGP) or between different ASes (external BGP).
  • Autonomous System Numbers (ASNs): Unique identifiers assigned to autonomous systems for BGP routing.
  • BGP Attributes: BGP uses attributes such as AS_PATH, NEXT_HOP, and others to determine the best path to a destination.
  • Path Selection Algorithm: BGP uses a specific algorithm to select the best route based on various attributes.


Establishing BGP sessions

  router bgp [AS-number]
  neighbor [peer-ip] remote-as [peer-AS]

Advertisement of routes

  router bgp [AS-number]
  network [network-address] mask [subnet-mask]

Route filtering and policy implementation

  router bgp [AS-number]
  neighbor [peer-ip] filter-list [access-list] out

BGP route aggregation

  router bgp [AS-number]
  aggregate-address [aggregate-address] summary-only

Best Practices and Optimization


  • Load balancing with variance: Adjust the variance to allow EIGRP to use multiple routes for load balancing.
  • Stub and leak map configurations: Utilize stub routing for simplified configurations in branch offices.
  • Query scoping: Configure EIGRP query scoping to limit the scope of queries during network changes.


  • Prefix lists and route maps: Use prefix lists and route maps for fine-grained control over route advertisement and acceptance.
  • Route dampening: Mitigate the impact of unstable routes by configuring route dampening.
  • BGP peering best practices:
    Implement best practices for securing and stabilizing BGP peering sessions.
  • Scaling BGP in large networks: Optimize BGP configurations for scalability in large and complex networks.

Security Considerations


  • Authentication mechanisms: Enable authentication using methods like MD5 to secure EIGRP communications.
  • Control-plane protection: Implement control-plane protection mechanisms to secure EIGRP processes.


  • BGP session protection: Use features like TCP MD5 authentication to secure BGP peering sessions.
  • Prefix filtering: Employ prefix filtering to control the routes that are accepted or advertised.

Monitoring and Troubleshooting


  • EIGRP topology table analysis: Monitor the EIGRP topology table to identify issues and optimize routing.
  • Log analysis and debugging: Use logging and debugging commands to troubleshoot EIGRP-related problems.


  • BGP table examination: Analyze the BGP routing table to understand the routes being advertised and selected.
  • Monitoring tools and commands: Utilize monitoring tools and commands (e.g., show bgp, clear ip bgp, etc.) for real-time analysis.
  • Troubleshooting common BGP issues: Use troubleshooting steps like checking BGP status, examining route advertisements, and analyzing logs to address common BGP problems.

Self Assessment

  • Reflect on the significance of advanced routing protocols in the context of large-scale networks and the challenges and benefits associated with their implementation.
  • Explain the key characteristics of Enhanced Interior Gateway Routing Protocol (EIGRP) and how it combines features of distance vector and link-state routing protocols.

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