Thursday, January 5, 2023

An Architectural Perspective on Hierarchy In IP Networks - A Complex Puzzle Comprising Protocols, Topologies, Addressing & Systems (A Short Post)

 


If you ever bump into a Network Design book, course, blog or a webinar - most likely you are going to get introduced to this interesting & an important concept of " Network Hierarchy aka Hierarchical Networks Design Principle ".

Now depending upon which study materials and authors you follow, you would likely to come across different view points in terms of it's needs, pros & cons. Which in general not only contributes into more confusion among audience but also when I speak around with experiences Network Architects & Design Engineers, I often find them:

1. Having different interpretations of this concept and different view points

2. Considering this to be a very theoretical concept which you are likely to encounter in most Architecture & Design books but don't know about:

A. How to practice it (By applying theory to practice) 

B. How to measure it 

C. Missing the deep understanding of the topic at hand beside failing to understand its tradeoffs

So Idea behind this post is to offer you some architectural decision pointers to think through the problem statement and break it down into few tangible pieces by following another important network design principle " Separate the Complexity from the Complexity - Russ White " beside examining the rule 8 from RFC-1925

One of the model I personally always find handy is the SOS model from Russ White and you can use it too as a good ref. point.


So here is the quick list for you to think through in a more pragmatic manner:

1. What problems are you really trying to solve by introducing hierarchy into the Network (Go beyond theory) ?

2. Is it always possible to follow hierarchy? Specially in brown fields or during transitions (Think of old gear with still some lifetime left, mergers )

3. What are the downsides of introducing hierarchy ? (What harm it can cause and tradeoffs such us downgrade Agility, Flexibility, Organic Growth etc.)

4. Difference between Hierarchy vs. Symmetry vs. Modularity vs. Abstractions 

5. Different types of hierarchy/ layered approach to it ( physical level hierarchy,  logical level hierarchy,  hierarchy in addressing scheme, Protocol Level Hierarchy (ISIS Levels & Addressing ?) and so forth)

6. What data points you have in place to test your hypothesis to measure its impact on network

7. How these concepts are applied to different network environments - Enterprises (Campus <Wired and Wireless>, WAN/SDWAN, DC) vs Teclos vs CDNs vs Cloud Providers vs Web Scales vs Within public cloud virtual DC + Controller vs. Controller Less Architectures

8. Impact of introducing hierarchy on Visibility, Reporting and Performance mgmt. of the network

9. Impact on hierarchy on information hiding <reachability information> vs. topological information hiding (Aggregation vs. Summarization)

10. How all these choices will flow into your equipment sizing and potentially have an impact on your decision process

11. How will you apply all these concepts in a IPv10 network (IPv4 + IPv6 aka Dual Stack)

12. And if you are still brave enough :) , read through the further readings list to get to the bottom of this rat hole

Further Readings:

P-FatTree: A Multi-channel Datacenter Network Topology

Enabling Wide-spread Communications on Optical Fabric with MegaSwitch

Abstraction in Networks with Russ White

Hierarchical Network Design Overview

Engineer Versus Complexity

Optimal Routing Design

Navigating Network Complexity

Network Topologies

Five Number Summary for Network Topologies

Scaling MPLS Networks

The Side Effects Of Route Summarization

Avoid Summarization in Leaf-and-Spine Fabrics

Valley-Free Routing

Intra-Spine Links in Leaf-and-Spine Fabrics

Nonblocking versus Noncontending

Hierarchical IP Address Design and Summarization

Hierarchical IPv4 Framework

Fabric versus Network: What’s the Difference?

Liskov Substitution and Modularity in Network Design

Dragonfly+: Low Cost Topology for Scaling Datacenters

Reliability Basics- Part1

Network Centrality and Robustness

Swimlanes, Read-Write Transactions and Session State

Fifty Shades of High Availability

HTH...

A Network Artist ðŸŽ¨

Wednesday, January 4, 2023

Overlay Networks & Protocols Tradeoffs - Aka SDN aka IBN aka Magic aka Silver Bullet

 


A long time ago I wrote a short article on what really went wrong with SDN, now a few years later the topic still pops up in a conversation with the great Ivan & he acknowledged my list of Tradeoffs (things to watch out for carefully) related to overlay networks and protocols which seems to be de-facto standard for most modern Network solutions that we see around in Enterprises & Telcos.

  • Impact of overlay networks on visibility, reporting and performance management
  • Additional control plane that would result in additional abstraction layers and interaction surfaces and hence cascading effect in many situations
  • Impact on troubleshooting: how many solutions do we see in the market that can correlate underlay and overlay problems?
  • When it comes to sizing equipment in terms of control plane or data plane, it poses a new level of complexity an architect would need to deal with and in most cases vendors themselves won’t be able to offer much help in general rather than just asking you to believe in their words
  • I see lot of VXLAN and EVPN preachers, but let’s agree that mapping VLAN to VXLAN on 1:1 basis tells me you don’t know your stuff and believe too much in vendor marketing
  • EBGP underlay with IBGP overlay…man we can do better
  • Stitching two EVPN DCs with MPLS and SR: most of the implementations that I have seen were too complex and too fragile and thus results in a complex “policy.”

Further Readings:

Disjoint Path Routing and LP

HTH...

A Network Artist ðŸŽ¨