Enterprise Core Routing Design Models with BGP

Reading through the well-written CCDE Study Guide book by Marwan Al-shawi, came to a section about having BGP as the Enterprise Core Routing Protocol and its possible Design models.

To make it a little bit brighter to myself, I’m gonna explain them in a different way with different diagrams and matrix based on my own design experience with these models.

Disclaimer: Please have in mind that the number of routers drawn, doesn’t reflect the reality of the design, and is just been this way for the sake of simplicity; obviously there would be redundant routers in real World, and also the Core could span different PoPs.
Besides, the bigger border routers could reflect two separate ones, one on Core, and one on Branch side.

Design Model 1

BGP-as-Enterprise-Core-Routing-Design-Model-1

This model is suitable when least Administrative Domain Control is required; though it still overcomes an end-to-end IGP design, providing better management between remote campuses.

Core IGP is mainly used to provide Next-hop reachability for iBGP speakers. Please note that this is applicable to all models where iBGP is used in the Core.

The downside to this design is moderate operation complexity; which could arise i.e. by IGP-into-BGP Redistribution and iBGP full-mesh/RR/Confederation management in the Core. Continue reading “Enterprise Core Routing Design Models with BGP”

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Network Design Project Initial Questions

I have been always thinking of creating a set of questions-to-be-asked for Network design projects. Though, it’s really hard to have the same template for every project, but usually there some general questions applying to all.

Skimming through the web, I came to an interesting article on Cisco Learning Network : Unleashing CCDE. I am pasting the questions list here, but with my own text marking:

Listed are some of the initial questions to ask your customers at the onset of a new network design project:

1. Business objectives, pain points and perceived constraints
  • Who are the key stakeholders, sponsors, end users?
  • Why is there a project in the first place? What are the drivers for the redesign of your existing network?
  • What are the current pain points?
  • Which business outcomes the customer expects to achieve?
  • What is the business growth plan 3-5 years, capacity planning, scaling requirements?
  • Are there any regulatory constraints such as HIPAA, PCI, Fed, and Local Government that affect the organization and industry? Other known constraints?
  • Is there specific equipment, vendors, or protocols preferred or are absolutely out of the question?
  • What are the implementation timelines and milestones?
  • What are the key success factors? Are there known barriers to success?
  • What is the customer tolerance to risk? Conservative or bleeding edge?
2. Desired characteristics and capabilities
  • What is the current state of the network (baseline), to compare after the implementation of the new design?
  • Are there any documentation available, features in use, versions, is standardization consistent?
  • What is the financial investment (cost/budget, cost-benefit analysis) x desired business, operational, and innovation outcomes, followed by a technical translation of these needs/goals to a technology environment?
  • What are the desired characteristics of the new network: redundancy/resiliency/convergence, speed, security, cost, application performance, simplicity, manageability, capabilities? Load balancing, load sharing?
  • Public, private or hybrid cloud?
3. Footprint, policies, method of access and traffic patterns
  • What is the geographical distribution, connectivity options/capabilities on the branches?
  • Where do the servers reside in the network, their known vulnerabilities and how the services align with the security policies?
  • What are the current and future traffic patterns, north-south, east-west, or both?
  • What are the current and future applications’ requirements and tolerance to delay, packet drop, and jitter?
  • What is the company security, infrastructure policies? Do you have specific design/architecture principles to adhere to? Any project management methodology or tools? Network management?
  • What are the established SLA’s if any, and the level of success achieved for these SLA’s?
  • Does the network support the business, the network is the business, or both?
  • Are there best practices?
  • Will there be a test lab or group, a prototype, a development area?
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BGP – Controlling the Entry Point (HLD)

From the BGP Design point of view (HLD), there are four options to manipulate the inbound traffic, MED, AS-path prepending, using communities, and breaking aggregated routes.

MED

This is not really useful, as it has to meet some conditions:

  • The AS-path of learned routes should be identical. Thus, this could be only useful when multihoming to the same AS.
  • The BGP peer might use Local-Preference in the Path Selection process.
  • Usually, Service Providers reset or strip received MED.

AS-Path Prepending

It’s not always helpful.

Continue reading “BGP – Controlling the Entry Point (HLD)”

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