Configuring ACLs - ACL Resequence

In this blogtorial we will see how ACLs are sequenced and how we can resequence if we need to. ACL's initially start with sequence number of 10 and increments each entry by 10 unless specified.

Let's take a look.

Propagating Default Routes - OSPF

How to get default routes into OSPF routing domain? Well, there is really just about one way to do it. It is by using default-information originate.

Consider this simple topology below and follow the screenshots.

Troubleshooting - Loop-back detected - %PM-4-ERR_DISABLE

Recently, I was tasked with troubleshooting a weird problem where one of the interfaces was err-disabled. Fun Monday mornings :) and sifting through the logs I came up on this error message. 

%PM-4-ERR_DISABLE: loopback error detected on Fa1/0/20, putting Fa1/0/20 in err-disable state

%ETHCNTR-3-LOOP_BACK_DETECTED: Loop-back detected on FastEthernet1/0/20.

Turns out that this was because of an interface somewhere in our network was configured incorrectly which then created a loop in our network. The STP topology in our network corrected/recovered itself within a few seconds and fa1/0/20 should have "err-disabled recovered", however "errdisable recovery cause loopback" was not configured. 

Basically this error message states that the keepalives which are on by default are looping back to the source interface.  

For example, if a keepalive was sent on fa1/0/20 and if that keepalive packet loops around the network and shows up at the source interface then that must mean that there is a loop in our network and the interface which sent out the keepalive will be err-disable.  

Notice that the keepalive are set to 10sec by default on all interfaces. 

Workarounds: 

• Fix the underlying misconfigured interface downstream and/or upstream.
• Disable keepalives on interfaces. 

Many more articles to come so stay tuned. "Join this site" on the right / click +1 below ------->

Propagating Default Routes - EIGRP

There are 4 ways to get default routes into EIGRP topology. We will take a look at all of them. Consider a simple 2 router topology and let's begin.

Configuring /31 - P2P or Segment with 2 endpoints

In general, most ISPs will assign a /30 on point-to-point interfaces which gives you 4 IP addresses and 2 of which are usable resulting in 50% of addresses in that subnet being wasted. For example 1.1.1.0/30 yields 1.1.1.1 and 1.1.1.2 as your usable IP addresses and 1.1.1.0 is the subnet number and 1.1.1.3 is the broadcast address. And as you can see only 2 out of the 4 IP addresses are usable. So how we can be more efficient? The use of a /31 subnet mask which gives you 2 IP addresses and 100% of them will be utilized.

Consider a very simple topology below and let's get started.

Configuring OSPF FAST hellos

The sooner we detect OSPF neighbor failure the faster the network can converge when there is a failure. In this blogtorial we will see how we can achieve fast detection of OSPF neighbor failure. Consider this simple 2 router topology and let's get started.

Preventing Sub-optimal routing in mutual redistribution - Part 1

Following from my previous redistribution post. Let's explore a few ways we can prevent sub-optimal routing from redistributing routes at multiple routers.

Consider the topology from my previous redistribution post and let's continue.

Configuring Mutual Redistribution - OSPF to RIP

In this blogtorial we will take a look at how to configure mutual redistribution between OSPF and RIP. Though it is very easy to configure, tweaking it and preventing suboptimal routing is tricky. However, we will save "Preventing Sub-optimal routing in mutual redistribution" for the next post.

Consider a very simple topology below and let's get started.

Configuring Frame Relay Point to Point and Point to Multipoint

It has been a while since I have written a blog. I have been very busy with life, new job and my CCIE studies. That's right folks, I have started my pursuit of the digits!! I will post my study materials, my schedule, and study plan on another post. In this blogtorial we will configure Frame Relay Point to Point and Point to Multipoint. We will build on this topology and configure EIGRP and explore topics such as split horizon and see how it affects route advertisments. Consider the simple topology below and lets get started.

Enterprise Campus Design - Part 1

In this blogtorial we are going to dive into how to effectively and efficiently design an enterprise network. As I have always said "Networking is an art not science" as there are numerous ways to design and I am merely posting one of many. 

In this topology we will sink our hands into: 

• STP (802.1d)
• HSRP
• OSPF 
• OSPF route summarization
• VTP
• Different layers/modules of Enterprise Campus Design

Check out the topology below and let's get started. 

Relevant configurations are posted below.

Configuring InterAS MPLS VPNs - CSC (Carriers Supporting Carriers)

In this blogtorial we will take a peek at how to configure InterAS MPLS. InterAS MPLS can be deployed to support customer sites traversing different SPs (Service Providers). 

In this topology we will have 3 customer Sites. 2 of them connection to two different PEs routers in the same AS and another site connected to another PE router in a different AS. 

Topology below and let's get started. 

Relevant configurations are posted below.

How to configure QOS with IPSEC VPN

In this blogtorial we will discuss how to do QOS with IPSec and the challenges that are associated with it. 

Consider the topology below and let's get started. 

Relevant configurations are posted below. 

Configuring MPLS FRoMPLS DLCI-To-DLCI

Recently, I have been posting about AToM (Any transport over MPLS) and to continue I will post how to configure Frame Relay DLCI-TO-DLCI in this blogtorial.

Consider this simple topology and let's get started.

Relevant configurations are posted below.

Configuring MPLS EoMPLS VLAN Mode - L2VPN

In this blogtorial we will configure EoMPLS VLAN mode so we can preserve the VLAN tagging from one site to another. Consider the simple topology and let's get started. 

Relevant Configurations are posted below.