Category Archives: Routers

Configuring MPLS L2 – Base/lab config

This example is how to configure basic Layer 2 MPLS connectivity across your MPLS core, so CE endpoints, or in some cases, ToR switches can appear to be layer 2 adjacent, through your core.  This is primarily used on the service provider side but has amazing uses for the data center end of things.  Being… Read More »

OSPF Neighbor Relationships

In this post, we will discuss the components involved with OSPF Neighbor Relationships.  This is not a configuration guide but should be used as a reference for various OSPF states and concepts that the OSPF protocol goes through to establish connections to its neighbors. Determine your own Router ID.  The router ID identifies the router… Read More »

OSPF Area Design and Terms

Here are some core concepts that go into understanding OSPF.  This is the number one IGRP in the world so it worth taking time to understand a few of these fundamental principles. The three tables used are the Neighbor table, the Topology table, and the Routing table. All routers must connect to Area 0.  Routers… Read More »

Routing in the Data Center

Types of Routes: Direct Route – Directly attached to the router interface. Static Route – Used to tell your router statically where to direct traffic: ip route Meaning can be reached via  This can be confirmed by viewing the routing table with: show ip route Dynamic Route – Determined using a… Read More »

Route Table Terms

These are terms commonly used with routing protocols to prevent loops and bad routes from occurring within your network: Hold down Timer – prevents a router from improperly reinstating a route from a regular routing update.  This causes the router to ignore any updates with poorer metrics to a lost network for a given period of time.… Read More »

WAN Connections: Frame Relay

Frame Relay is typically used in packet switched networks.  Packet switched networks let service providers share unused bandwidth across lines.  This allows the service provider to sell cheaper connections since you may not use all of the bandwidth.  They can also over provision the cloud they are sharing. The terms to know are as follows:… Read More »

Cisco WAN Links: PPP (Leased Line) Protocol

Typically with WAN connections, you connect your WIC (WAN Intenret Connection Card) using a DB-60 connector (serial interface) to a CSU/DSU with the V.35 side of the cable.  The CSU/DSU then connects into the wall which is the DEMARC. The other physical type of connection is a card that combines the CSU/DSU into the card… Read More »

Cisco Router NAT Configuration

Configuring NAT Overload: These configurations will take place on your internet router since this is where NAT needs to happen.  The steps to configure NAT Overload are as follows: Label Interfaces Identify internal IP addresses to be translated Enable NAT overload 1: conf t int e0/0 – our inside interface ip nat inside – tells… Read More »

The 3 styles of NAT

Dynamic NAT Dynamic NAT is a one to one NAT, however you setup an IP pool of NAT’d IPs so when devices cross networks it will NAT them to the pool created.  It can also work in conjunction with DNS to assist with overlapping address ranges.  This is the least common form of NAT. NAT… Read More »