Recap: VLAN Trunking Protocol

Cisco VTP – the VLAN Trunking Protocol is a management tool for large L2 deployments. It provides a simple way to synchronize VLAN names and numbers across Cisco switching infrastructure, also automates some traffic optimizations (the VLAN pruning).

VLANs & Trunking

A quick recap: Virtual LANs and Trunking in Cisco Ethernet switches. There are different VLAN ranges, switchport modes and some ways to manage all that.

Routing Protocols over On-Demand circuits

This is the second post about Demand in Routing. In the first post I covered some common demand-related points and Cisco On-Demand Routing. In today’s post I write a little about Routing Protocols and their behavior over on-demand circuits.

Making sense of all the demands in routing

Apparently, there are several very distinct topics in routing which have the word “demand” in them. First, there is Cisco On-Demand Routing quasi-protocol, and then there are on-demand circuits which routing protocols must treat differently. Last but not least, the on-demand circuits are used for Routing Backup.

VRF Lite basics

Sometimes while you do routing, you want to do it in a destination-based way and also differentiate routing for different sub-autonomous systems in your AS. Well, such behavior can be enforced by PBR, but it is not that scalable and it lacks some of the nicer things dynamic routing protocols bring to the table. Enter Virtual Routing and… Read More »

How to write long iterative configs

Sometimes there is a problem: you need to write a really repetitive config with hundreds of nodes. Clear example would be dial peers in Cisco routers. It is immensely hard and dull to do this by hand or copy+paste. Here’s a simple python script to do it for you.

Dual-homing with Policy-Based Routing – a case study

Policy-based routing allows network administrator to stir traffic in directions different from the one chosen by destination-based routing and its routing protocols. This can be useful in several scenarios, namely in dual-homing to different ISPs, as well as other special cases. Using policy-based routing for dual-homing General notes on dual-homing The term Dual-homing in its most general meaning… Read More »

Policy-based routing for IP networks

Policy-based routing for IP networks in Cisco routers is a very powerful and precise tool which allows a network administrator to achieve a great many things.  In my opinion it should be considered just as fundamental, as general routing mechanisms. How  it is different from general destination-based routing and what we can to with it is the subject… Read More »

General IP Routing

Internet Protocol Routing, nowadays commonly known as L3 Switching, is part of the process of forwarding an IP packet from Source to Destination. Interestingly, it happens more often then commonly understood: even on a common subnet we often need to make an IP routing decision.

How many hosts can we handle? – Part 1

Here comes a really tough design question from one of my co-workers: What is a good estimation of the maximum number of hosts per ethernet domain (i.e. VLAN)? Well, when I was first studying networking in college, we generally accepted that about 250 hosts should be the limit and enough for everybody. It was years ago, so let’s… Read More »

VLAN allocation

Speaking of L2 design, there are several aspects to the VLAN allocation on the switches: standard and extended VLAN ID ranges, reserved IDs, internal usage, protocol limitations and design best practices.