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Apache benchmarking (ab) commands cheat sheet

Apache benchmarking (ab) commands cheat sheet

Apache benchmarking tool (AB) command line basic cheat sheet with brief description for each command. you can use AB to load test http servers directly from the command line....

Openstack Neutron Overview

Openstack Neutron Overview

The Openstack Networking service (Neutron), provides an API that lets you define network connectivity and addressing in the cloud. The Networking service enables operators to leverage different networking technologies to power their cloud networking. ...

Data Center Network Fundamentals

Data Center Network Fundamentals

The following collection of posts will lay out the foundation of understanding basic concepts of data centre network design and explains the role and importance of BGP in the modern datacenter network. We hope that you find them useful. ...

L3 fabric DC -The underlay Network (BGP) -part2

L3 fabric DC -The underlay Network (BGP) -part2

In the previous post, we laid the foundation of L3 fabric DC In this post we will discuss the underlay network which mainly provide IP reachability plus ECMP capability, here BGP would play a role in your DC next to the 3 other that we d...

L3 fabric DC -The underlay Network -Part1

L3 fabric DC -The underlay Network -Part1

In the previous posts we have discussed the classic DC designs and the M-LAG solution. In this post we will cover the basic L3 fabric DC, you might never heard of it or you think that’s a solution for massive scale DC, yes the massive DC i...

TCP Protocol: Slow Start

TCP Protocol: Slow Start

In the last post we explained the basic idea of using sequence and acknowledgement numbers to track how many bytes were sent and received. We also has encountered the term "slow start" and elaborated how TCP uses this concept on the server ...

TCP Protocol: Flow Control

TCP Protocol: Flow Control

In the last two posts here and here, we have discussed how TCP stack initiates a TCP 3-way handshake and create the appropriate Transmission Control Block for the data to flow reliably. We knew that the main function of the 3-way handshakin...

Classic DC and M-LAG

Classic DC and M-LAG

In the pervious post we talked  about BGP in Data Center and how it is a topic of discussion in between the DC and the SP arenas. In this post I will start explaining some classic DC design and laying its shortage which will engage the S...

BGP in the Data Center

BGP in the Data Center

If you think that BGP is a Server Provider (SP) only protocol and is not your business in the data center, then better think again because BGP is coming to your territory. Traditionally for Enterprises and DCs; BGP commonly took part at ...

What is 6PE?

What is 6PE?

6PE is one of the efficient solutions for interconnecting IPv6 islands over an IPv4-only MPLS cloud without needing to drastically change the core network design by having all your Core routers dual-stacked 6PE does not use manual standa...

CCIE SPv4.1 Blueprint Resources

CCIE SPv4.1 Blueprint Resources

The CCIE SP SME team has put a comprehensive list of study resources for the new CCIE SP4.1 blueprint. The complied list is in a spreadsheet designed to help you quickly find what you are looking for by organizing the content according to t...

TCP Protocol: TCP 3-way handshaking #2

TCP Protocol: TCP 3-way handshaking #2

In the last post, we have explained the TCP 3-way handshaking from an abstract point of view, and knew that one of the main functions of this handshaking is to exchange and synchronize some parameters for the TCP connection endpoints to fac...

TCP Protocol: Three-way Handshake

TCP Protocol: Three-way Handshake

We all know by now that the basic function of the TCP protocol is to send a stream of bytes that has no shape or fixed size over a network reliably to a receiver. We all also know that reliable delivery involves building a connection bet...

TCP Protocol: The Overview - Part1

TCP Protocol: The Overview - Part1

One of the most important layers we - as network engineers - hate and avoid in the OSI reference model is the transport layer with its popular and dominant protocol; TCP. Most of network engineers abandoned diving into TCP protocol becau...

JUNOS Disable vs Deactivate interfaces

JUNOS Disable vs Deactivate interfaces

Confusing between disabling and deactivating interfaces on JUNOS is a common mistake that leads to all sorts of problems during implementing changes on live network boxes. Let's look and clarify the differences quickly. Disabling an inte...

Find the difference between dates in Python Example

Find the difference between dates in Python Example

A quick example for find the difference in days between two dates in python using the datetime standard library package....

Introduction to Software-Defined Networks

Introduction to Software-Defined Networks

SDN, Software-Defined Networking, the trending technology that is making big changes for how we do networking today, This is an introduction for beginners to learn What SDN is about. Let's see if it does some thing. SDN has been a market hype for few years now.  Out of lazines...

How to become a Network Engineer?

How to become a Network Engineer?

If you aspire to become a network engineer, this post is going to guide you in making up your mind. Read through. From the outside, the whole information technology profession can seem mysterious. Mentioning IT summons various images ran...

Troubleshoot#2: Core Dumps for Network Engineers

Troubleshoot#2: Core Dumps for Network Engineers

Got a core dump file, please contact your TAC engineers for further support ! This is the common statement that we all see on vendors' websites and in their recommendations and it definetly is true.  The reason is that a core dump file...

150+ Linux and Devops tools Cheatsheets

150+ Linux and Devops tools Cheatsheets

How often do you find yourself scratching your head, trying to remember a command that you knew by heart but just can't remember when you need it most? Megash is a 150+ cheatsheets for devops, programmers and linux admins in one page to make your daily work much easier....

Making Sense of Broadband networks: PPPoE Explained

Making Sense of Broadband networks: PPPoE Explained

A bit of background First .. PPPoE stands for Point to Point over Ethernet and is the successor of PPPoA. PPPoE is simply a method of encapsulating PPP packets into Ethernet frames. The standard is defined in RFC2516 . IPoE is growing very...

Understand MTU and MRU - The Full Story

Understand MTU and MRU - The Full Story

MTU or Maximum transmission unit is a topic that pops up every once in a while in different discussions. Although it's a simple concept, it causes a lot of confusion specially for those who are new to the field. MTU typically becomes an iss...

Troubleshoot#1: Correlation vs Causation

Troubleshoot#1: Correlation vs Causation

Network problems can be as simple as follows: Ping neighbor. 100% packet loss. Check network interface, it's down. Change SFP and you are done, problem solved :)   But they can also be complex; really complex .. In the past ...

text2pcap - How to convert ASCII packet dumps to .pcap files?

text2pcap - How to convert ASCII packet dumps to .pcap files?

Nothing in my experince is better at telling the real story than a packet capture. They tell exactly what is really going on and whether the configuration or changes are working  as expected or not. Sometimes an engineer needs to look at pa...

PPPoE MTU Explained

PPPoE MTU Explained

PPPoE MTU is a buzz word that many people ask about even if they don't have anything to do with network engineering. Just being a broadband subscriber with a PPPoE circuit is enough to get introduced to the concept. In this post I will b...

What is MTU?

What is MTU?

MTU stands for Maximum transmission unit, which is the maximum packet length that can be sent on an egress interface toward a destination. MTU is an attribute of the egress interface and is typcially considered over a full path from the sou...

Making sense of Broadband networks – VLAN Model

Making sense of Broadband networks – VLAN Model

In the previous post we discussed the major considerations of a broadband network architecture. Now I want to discuss each of those points one by one adding some details. I will do this quick and might not be able to provide illustrations o...

Making sense of Broadband networks - Part 1

Making sense of Broadband networks - Part 1

Broadband is a hot topic in the telecommunications industry nowadays; it is becoming the bread and butter for so many service providers and mobile carriers with the big growth and penetration rates in these technologies in the recent years....

What can you learn in 5 minutes a day !

What can you learn in 5 minutes a day !

I  believe in minimalism and what small focused actions can make for a person and small steps is what Juniper learning bytes is all about. Learning bytes is an online learning resource launched last year by Juniper education services organi...

DHCP client testing tool

DHCP client testing tool

DHCP is vastly growing in service provider networks for broadband subscribers, I had the chance to work lately with a some of these setups. The protocol is really easy to configure for broadband and provide many benefits.  It has lower over...

Few ways scripting can keep you sane

Few ways scripting can keep you sane

C'est la vie, it has been almost a year since I posted on the blog, a year full of change,  but here I am kicking up again with this simple short post about how scripting could save you time and effort on daily basis. I know most of you ...

BGP Weight Attribute

BGP Weight Attribute

BGP weight attribute is a Cisco proprietary path attribute that is local to the router and is used to influence local path selection on a certain router. BGP weight is the first in the list: BGP weight is the first tie breaker for best pa...

IPv6 Tutorial

IPv6 Tutorial

This is a collected IPv6 tutorial form IPv6 posts we have written and should be a good starting point for anyone who is just learning about IPv6. IPv6 was first formally described in Internet standard document RFC 2460. IPv6 offers more ...

BGP Attributes List

BGP Attributes List

BGP Attributes are pieces of information that a BGP router attaches to describe different prefixes included in it's BGP update messages. There is a variable sequence of BGP attributes in every update message except for those that carries on...

The Importance of Networking

The Importance of Networking

Networking is constantly being promoted throughout a huge range of industries, and is generally being seen as more valuable than ever before. However, all too often, it can be swept under the carpet. Those of us who work with technical indu...

The Forgotten skill of technical writing

The Forgotten skill of technical writing

It's a beautiful sunny day that puts a big smile on my face and I want to share it with you, so please put a big smile on your face now and before you continue. Your smile will make my day even brighter. OK, back to our post but keep smi...

IPv6 Tutorial: IPv6 Unicast Address

IPv6 Tutorial: IPv6 Unicast Address

To refresh our memories, we started our IPv6 tutorial  with an overview then we moved to IPv6 addressing in general and in this post I am moving deeper into IPv6 addressing types. As promised I will keep things simple and clean for you and ...

Life Follows a Plan, but the Plan is not Yours !

Life Follows a Plan, but the Plan is not Yours !

70 days passed since I wrote my last post about IPv6 Addressing. Long time, however I didn't feel it. Maybe I even forgot what I was doing here or planning to do, those 70 days actually carried a lot of unplanned events. My last post was...

Private IP address ranges

Private IP address ranges

IPv4 Private Address Ranges:   10.0.0.0/8 IP addresses: 10.0.0.0 -- 10.255.255.255. 172.16.0.0/12 IP addresses: 172.16.0.0 -- 172.31.255.255. 192.168.0.0/16 IP addresses: 192.168.0.0 – 192.168.255.255   Private IPv4 internet ...

IPv6 Tutorial: IPv6 Addressing #1

IPv6 Tutorial: IPv6 Addressing #1

I am back again with the second post in this series, in the first post we had an overview of IPv6 and the need for it in the near future. In this post we will start breaking the technical ice of IPv6; I am going to discuss basic IPv6 addres...

IPv6 Tutorial: The overview

IPv6 Tutorial: The overview

I will start from the beginning; two weeks ago I wrote a post claiming that IPv4 is depleting and IPv6 is coming soon; and since we are considering deploying IPv6 soon in our network, I thought it might be useful to write about IPv6 migrati...

7 Actions to get your network ready for IPv6

7 Actions to get your network ready for IPv6

IPv4 is depleting so fast and time comes to get ready for IPv6. IPv6 may come to real life by 2012/2013. I am making a big claim here and I think I need to back it up with some facts: IPv4 address space is estimated to deplete somewh...

I'm not the only one intrested in Huawie strategies

I'm not the only one intrested in Huawie strategies

Yesterday I had a post named "What do you think of Huawei?"; I am interested in their business strategies trying to gain a better understanding of the Telecom market dynamics, but it seems that I am not the only one interested in them. P...

BGP Attributes: Local Preference Attribute

BGP Attributes: Local Preference Attribute

The local preference attribute is a well-know discretionary attribute. This means local preference must be recognized by all BGP implementations, but will not exist in all BGP update messages; specifically it will not exist in E-BGP update ...

BGP Attributes: Atomic Aggregate Atribute

BGP Attributes: Atomic Aggregate Atribute

Atomic aggregate is a Well-known Discretionary attribute; it must be recognized by all BGP implementations and does not have to exist in all BGP updates. The purpose of the attribute is to alert BGP speakers along the path that some info...

BGP Attribute Types and Flags

BGP Attribute Types and Flags

BGP attributes is an interesting subject of study.  BGP is a very flexible and extensible protocol and I like that, let's see how flexible is that protocol when it comes to attributes handling. We all know that BGP has four types of attribu...

Measuring your SUCCESS

Measuring your SUCCESS

Try to ask five different persons about what success means to each of them and you will get at least five different answers. Try yourself Now: What is your definition of SUCCESS and do you consider yourself successful?. For me, success i...

MPLS Label Distribution: LDP Part3

MPLS Label Distribution: LDP Part3

So far so good, we have finished two parts of LDP and in this post we are going to explore another function of the four major functions of LDP. After an LDP session is initialized, LDP peers start to exchange label mappings according to ...

MPLS Label Distribution - LDP Part2

MPLS Label Distribution - LDP Part2

In my previous post I listed the main four functions of the label distribution protocol LDP and explained some concepts. In this post lets start dealing with the first two functions: Automatically discover LDP Peers in the same network ...

MPLS Label Distribution - LDP Part1

MPLS Label Distribution - LDP Part1

MPLS Label distribution protocol (LDP) as its name implies was defined to automatically create and maintain Label switched paths (LSP) in an MPLS network via label distribution. LDP specifications are defined in RFC 5036. In brief LDP as...

How to: use IS-IS overload bit

How to: use IS-IS overload bit

Overload bit is special bit in the IS-IS LSP used to inform the network that the advertising router is not yet ready to forward transit traffic.  The overload bit was first intended for signaling overload or resource shortage on specific ro...

Before you buy a Console Server

Before you buy a Console Server

In my post about out of band management networks I mentioned console servers as a mean of providing centralized remote access to network devices collocated in the same site. This post is a complementary post for the previous one if you are ...

Out of Band Management Networks - Console Servers

Out of Band Management Networks - Console Servers

Building a robust out of band management network is a critical part of any service provider or large enterprise backbone. Although failures may not occur frequently but believe me if you are not prepared when they happen you will know how O...

Cisco Profit up 79% Stock down 8%

Cisco Profit up 79% Stock down 8%

Last Wednesday Cisco announced its fourth fiscal quarter financial reports. Cisco reported a 79% jump in profit however its stock price fell down by 8% in after hours trading as sales were slightly below analysts' expectations. The question...

What you need to know about ADSL (broadband Networks #1)

What you need to know about ADSL (broadband Networks #1)

ADSL !!! I can hear you say "I know everything about ADSL, its a mature technology and I already know it inside out, why is he  writing about ADSL now?" To be honest I am also surprised by writing about ADSL after working with it for ...

The endless story of OSPF vs IS-IS - Part 4 "The Inside Out"

The endless story of OSPF vs IS-IS - Part 4 "The Inside Out"

In this post we'll be covering a couple of topics from the Inside Out of the link-state protocols that have always been ambiguous and full of details, we'll try to make them as crystal clear as we can. MTU: Both link-state routing pro...

The endless story of OSPF vs IS-IS - Part 3 "Packets and Database"

The endless story of OSPF vs IS-IS - Part 3 "Packets and Database"

In this post we are going to cover the protocol packets and database structure for both routing protocols. To start let's first highlight a couple of facts. OSPF runs on top of IP, that is it uses IP packets to exchange its messages (and...

The endless story of OSPF vs IS-IS - Part 2 "The history"

The endless story of OSPF vs IS-IS - Part 2 "The history"

In our previous post we started consolidating the endless story of OSPF vs IS-IS, in this post we will cover the historical part of the story, it might not be interesting for some people, but I do believe that the history is what makes the ...

IS-IS DIS in Practice

IS-IS DIS in Practice

In the previous post IS-IS Neighbor Discovery we have discussed how IS-IS automatically discovers neighbors, in this post we will discuss the DIS role in broadcast networks. After the adjacency state reached the UP state the DIS election...

IS-IS Neighbor Discovery

IS-IS Neighbor Discovery

Like other routing and signaling protocols IS-IS has built-in automatic neighbor discovery mechanism which is known by IIHs (IS-IS Hello PDUs), because IS-IS is not IP based protocol the IIH PDUs and all other IS-IS PDUs are directly encaps...

The Role of BGP in MPLS networks

The Role of BGP in MPLS networks

In almost every book you will read about MPLS, the author will state that one of the MPLS benefits is having a BGP free core network; sometimes they explain it sometimes not. However, to really understand this statement I encourage you to i...

The endless story of OSPF vs IS-IS

The endless story of OSPF vs IS-IS

Whenever you have a little IGP chit chat you'll hit this endless story. I've tried to reach a final solid conclusion my self but IMHO its all about personal preference and taste. It is something like a Ferrari vs Lamborghini story, they off...

MPLS Label Operations

MPLS Label Operations

In my previous post I explained what MPLS is and how it works from a high level perspective. In this post I will explain MPLS label operations and how labeled packets are processed in MPLS networks. When a labeled packet is received the ...

What is MPLS?

What is MPLS?

What is MPLS? MPLS stands for Multi-protocol Label Switching. MPLS is a packet forwarding technology that is capable of carrying any L3 protocol and here comes the word multi-protocol. MPLS is capable of tunneling L3 packets inside the MPL...

BGP Route Refresh Capability

BGP Route Refresh Capability

Service Providers or Large enterprises commonly change routing policies from time to time, specially when adding new links or peering relationships with other entities. When you change the inbound policy of your BGP speaker you need to r...

IS-IS MTU Mismatch

IS-IS MTU Mismatch

IS-IS is a link-state routing protocol, it uses the concept of distributed map/database and local computation , each router originates an LSP to describes himself , this LSP carries links and topological information, reach router on the dom...

BGP 4-Byte ASN

BGP 4-Byte ASN

The internet growth is awesome, day by day people recognizes how  internet is important in their daily personal  and business life and even for their culture, so the internet has a good bit of newbie everyday which depleted some internet re...

BGP Security

BGP Security

BGP is a critical component of the internet, bring BGP down and you bring the internet down or at least large portions of the internet. The problem is that BGP is highly vulnerable to many types of attacks for its implementation. BGP run...

Choosing PE-CE Routing protocol

Choosing PE-CE Routing protocol

When it comes to choosing your PE-CE routing protocol, Which one do you think is best? Choosing the PE-CE routing protocol for MPLS VPN  is an ongoing debate between back end network teams and those who have customer interface roles. The...

BGP Routing Information Base (RIB)

BGP Routing Information Base (RIB)

BGP is an intimate friend for all service provider engineers. Without BGP there is no internet, there is no MPLS VPN and there are no many other things now and in the days to come. I believe its healthy to visit your friends from time to ti...

MTU and ping size confusion

MTU and ping size confusion

I am very glade to return back after pausing posting for a while. Actually we were very busy the last few months evaluating, designing and preparing for our company's backbone migration, a little C Vs J with all its fun ;) Anyway, while ...

How to select your core routers?

How to select your core routers?

This question comes to my mind every time we are faced by choosing a new device for our network or whenever I read about hardware architecture of networking devices. However, when the time comes for  choosing routers for a large network mig...

CRS-1 Hardware Overview

CRS-1 Hardware Overview

After introducing the Cisco  CRS-1 router in a previous post, We are going to delve more into the hardware architecture of this router. I believe we have to start by defining the main hardware components of the CRS-1 router and briefly desc...

Carrier Routing System (CRS-1) Overview

Carrier Routing System (CRS-1) Overview

We have finished the physical installation of our CRS-1 routers this week, so I thought it would be nice to have some discussions about CRS-1, Juniper T-series and some general high end platform concepts. I believe this will be a series of ...

BGP table analysis and statistics

BGP table analysis and statistics

For those of you who are interested in obtaining some useful information about the BGP table (Internet routing table), check out the following websites for some useful reports, analysis and statistics. Nice resources for daily work, researc...

Cisco or Juniper, Which one should I choose?

Cisco or Juniper, Which one should I choose?

Being in charge of choosing the right boxes for a service provider network is definitely a hard task specially if it is a large network migration and this is exactly what we were doing in the past few months. The challenge here is that your...

VRF Selection Based on Source IP Addresses

VRF Selection Based on Source IP Addresses

In this post we are going to cover a nice tool, actually I've never used it in production, but I was fully testing it during my CCIE SP lab preparations and wish to share it with you. It's nice to have such a tool in your tool box when deal...

CEF and load sharing

CEF and load sharing

Load-sharing is one of the clumsy areas that is full of confusing parts. In this post we should be covering its ABCs, and latter on we should be covering more parts in details. We chose the name "CEF and load sharing" as the post name due t...

BGP Next-hop address tracking

BGP Next-hop address tracking

In this post we are going slightly deep into BGP operation on the CISCO IOS. Lets start this by discussing the BGP scanner operation, then we can talk about the next-hop address tracking feature. For each route installed in the BGP table...

Why BGP?

Why BGP?

This question is mostly repeated by newbies when they start learning about BGP and sometimes it is left unanswered clearly. In the simple dialogue below I will try to explain when BGP is mostly used and why? Can we connect two or more ne...

IS-IS and fast convergence ongoing tricks

IS-IS and fast convergence ongoing tricks

Been a while since my last post, I was extremely busy doing a lot of things, anyway I am glade to be back. This post I am going to cover a nice tool for enhancing IS-IS convergence, I am really amazed by the ideas that the guys out there...

OSPF & IS-IS Router ID

OSPF & IS-IS Router ID

When you think about Router ID in any link state protocol  two requirements come to mind: Each router must be identified by a Router ID and an Area to exist in. This Router ID must be unique inside a single IGP domain. IS-IS refers...

Jumbo Frames

Jumbo Frames

In the past few days we have been doing some tests for Ethernet MTU "The never ending story" in our MPLS backbone.  Playing with MTU for long may have bad effects on your health on the long run :) but is still a must to have an operational ...

Link state protocols and Areas concept

Link state protocols and Areas concept

Link state protocols have introduced the concept of multiple routing areas withing the same routing domain. Link state protocols depend on the fact that all routers must have an identical link state database and then each router will start ...

Black hole filtering

Black hole filtering

Black hole filtering is a technique usually used by service providers for traffic filtering without applying access-lists. The technique is very useful in mitigation of many types of DOS attacks. The idea behind Black hole filtering is ...

VRF Lite

VRF Lite

// The word VRF stands for Virtual Routing and Forwarding, this feature...

BGP Route Reflector Basics

BGP Route Reflector Basics

Everyone who ever studied BGP knows that BGP has strong rules to prevent routing and updates loops. In this post I will focus on iBGP loop prevention and specifically route reflectors as a result. The rule states: that any route received...

Interview with Emmanuel Conde

Interview with Emmanuel Conde

Today I have a special treat for you — an exclusive written interview with the CCIE Agent Emmanuel Conde. Eman (Emmanuel Conde) has the distinction of being the only CCIE recruiter promoted by World Wide Channels of Cisco Syste...

What is ARP and How it works?

What is ARP and How it works?

Address resolution protocol (ARP) is a building block or modern networks, in this post we are exploring how it works with examples from Cisco router. ...

MPLS VPN security threats

MPLS VPN security threats

MPLS L3 VPN services is widely used nowadays by many enterprises and organizations. They provide a lot of flexibility in connecting different sites compared to L2VPN services and offloads a lot of the responsibilities from the enterprise to...

Static routes and next hops

Static routes and next hops

Today I have received a question by mail from one of our readers asking about the difference between pointing the static route to a next hop address or pointing it to the exit interface itself as shown in the example below: !-- Pointing to...

LDP neighbor discovery, session establishment and maintenance

LDP neighbor discovery, session establishment and maintenance

Team working is all about producing results with a group of people you love working with … Being part of the same team, working together all day long we decided to extend this level of team working from being members of the same team and wr...

BGP performance tuning - Convergence, Stability, Scalability and NSF (Part 3)

BGP performance tuning - Convergence, Stability, Scalability and NSF (Part 3)

Lets continue our BGP performance tuning discussion. Sorry for the long delay but I was deeply busy in some other stuff. During the last couple of days I've attended Cisco Expo 2009, and during the SP - IP Core Technical Breakout, the br...

What is LDP extended discovery?

What is LDP extended discovery?

Normally LDP neighbors are found automatically by sending UDP Hello packets on Port 646 with the destination of multicast address 224.0.0.2 out of each LDP enabled interface. In some MPLS applications a LDP session must be established be...

Draft Martini, Draft Kompella and L2VPN services

Draft Martini, Draft Kompella and L2VPN services

Draft Martini and Draft Kompella were the starting points toward standardizing the Layer2 VPN architectures using pseudowire emulation, both drafts addressed setting up pseudowire emulation over MPLS-based networks in order to offer Layer 2...

MPLS Special Labels

MPLS Special Labels

MPLS label range from 0 to 1,048,575 (configurable on Cisco IOS) Labels 0 through 15 are reserved labels. An LSR cannot use them in the normal case for forwarding packets, the labels from 16 through 1,048,575 are used for normal packet forw...

Static Routes Label Binding

Static Routes Label Binding

In this post we will be discussing the label binding for static routes and the forwarding of labeled packets destined to these destinations. IP routing protocols build the IP routing table, and each LSR assigns a label to every destinati...

Carrier Supporting Carrier - The whole story (2)

Carrier Supporting Carrier - The whole story (2)

In this post we are going to discuss both CSC options that we have highlighted in the previous post in details. The two available options are either an ISP customer carrier, or a BGP/MPLS VPN customer carrier. We are going to conquer the...

Carrier Supporting Carrier - The whole story (1)

Carrier Supporting Carrier - The whole story (1)

After I've completely illustrated the Inter-AS MPLS VPN solution with all its options, I've decided to cover the Carrier Supporting Carrier with all its options as well. It was described as Carriers' Carriers in draft-ietf-2547bis sectio...

Inter-AS MPLS VPN - The whole story - Updated Dec 2008

Inter-AS MPLS VPN - The whole story - Updated Dec 2008

While doing the final preparations for my CCIE SP track written exam, I reviewed my Inter-AS MPLS VPN posts and I found out that they needed some modifications to be more organized and comprehensive, please revisit the updated posts: Int...

What is BGP 4-byte AS number?

What is BGP 4-byte AS number?

Today, we received an email from AfriNIC stating that starting from January 2009 they are going to assign 4 bytes AS numbers by default unless otherwise specified. They are asking providers to upgrade their routers to support the new format...

BGP performance tuning - Convergence, Stability, Scalability and NSF (Part 2)

BGP performance tuning - Convergence, Stability, Scalability and NSF (Part 2)

As we agreed in the last post, we are going to discuss the available tools and parameters for BGP performance tuning. In this post we are going to start discussing the different types of timers that BGP uses for its operation. BGP networ...

MPLS control and forwarding planes

MPLS control and forwarding planes

Control plane as defined in previous posts is the part of the router architecture that is responsible for collecting and propagating the information that will be used later to forward incoming packets. Routing Protocols and label distributi...

Fast Convergence: IS-IS performance tuning

Fast Convergence: IS-IS performance tuning

IS-IS is the most selected protocol by service providers and large carriers all over the world; this is what makes the understanding  of this protocol important. We have been discussing fast convergence and high availability in the latest f...

BGP performance tuning - Convergence, Stability, Scalability and NSF (Part 1)

BGP performance tuning - Convergence, Stability, Scalability and NSF (Part 1)

It is a very critical matter for a network architect (the same goes for a network operator but with a different prospective) to understand the inside out of tuning the routing protocols performance, in order to be able to conduct an appeali...

Fast Convergence: Partial SPF calculation

Fast Convergence: Partial SPF calculation

Shortest path first (SPF) is the algorithm used by IS-IS and OSPF routing protocols to calculate the topological information from the received link state updates. You can find more information about SPF calculation follow the link Dijkstra'...

Real job description for a Network Architect

Real job description for a Network Architect

Guys, I would like to share with you the real description of the Network Architect job. Enjoy reading...

Fast convergence overview

Fast convergence overview

For a network to converge, all routers in the network must collect and agree on all the topology information from each other. This information must be consistent, reflecting the current state of the network and free of routing loops or any ...

Cisco and Nonstop Forwarding

Cisco and Nonstop Forwarding

Nonstop Forwarding is a feature of many features in the Cisco High Availability portfolio, we shall be covering most of it later. To check Cisco High Availability portfolio: http://www.cisco.com/en/US/products/ps6550/products_ios_tech...

Option AB - Inter-AS MPLS VPN - The whole story (5) - Updated Dec 2008

Option AB - Inter-AS MPLS VPN - The whole story (5) - Updated Dec 2008

In late 2007, Cisco introduced a new Inter-AS option; Option AB - This feature was introduced in the 12.2(33)SRC code. This feature combines the the best aspects of Option 1 (10A) and Option 2 (10B) (named type a and type b as per RFC4364 s...

Option 3 (10C): Multi-Hop MP-eBGP Between RR and eBGP Between ASBRs - Inter-AS MPLS VPN - The whole story (4) - Updated Dec 2008

Option 3 (10C): Multi-Hop MP-eBGP Between RR and eBGP Between ASBRs - Inter-AS MPLS VPN - The whole story (4) - Updated Dec 2008

This approach is considered to be the most scalable, since when compared with Option 2(10B), the ASBRs need not learn all the VPNv4 prefixes, since now the MP-eBGP session will be established between the RRs (which already have all the VPNv...

Option 2 (10B): ASBR-to-ASBR / MP-eBGP for VPNv4 - Inter-AS MPLS VPN - The whole story (3) - Updated Dec 2008

Option 2 (10B): ASBR-to-ASBR / MP-eBGP for VPNv4 - Inter-AS MPLS VPN - The whole story (3) - Updated Dec 2008

With the ASBR-to-ASBR approach, the ASBRs use MP-eBGP to peer with each other to transport VPNv4 routes between the autonomous systems, and the VPN packets are transported as labeled packets between the ASBRs, unlike Option 10A. As we ar...

Option 1(10A): Back-to-Back VRF - Inter-AS MPLS VPN - The whole story (2) - Updated Dec 2008

Option 1(10A): Back-to-Back VRF - Inter-AS MPLS VPN - The whole story (2) - Updated Dec 2008

Well, lets start examining the different options that we have highlighted in the previous post one by one, in this post we shall be covering Option 10A (Type A as described in RFC 4364). The VRF-to-VRF (as stated in RFC 4364) or the back...

L2VPN Pseudowire Redundancy (MPLS AToM Redundancy)

L2VPN Pseudowire Redundancy (MPLS AToM Redundancy)

The MPLS L2VPN is growing exponentially,  back to the old days, customers were preferring FR and ATM VPN model due to the weakness of  Peer-to-Peer VPN model at this time, but after MPLS become fact on  the ground most of these customer mig...

IS-IS explained Part2 (Routing Levels)

IS-IS explained Part2 (Routing Levels)

The concept of Areas was introduced in OSPF or link state protocols in general and routers had different roles based on their location in the topology. We have backbone routers, Area border routers, ASBRs and so on. IS-IS is implementing th...

What is Integrated ISIS?

What is Integrated ISIS?

The IS-IS Routing Protocol may be used as an IGP to support IP as well as OSI. This allows a single routing protocol to be used to support pure IP environments, pure OSI environments, and dual environments. Integrated IS-IS is deployed exte...

IS-IS explained (Part1)

IS-IS explained (Part1)

IS-IS was developed for OSI routing then extended to support IP by Integrated IS-IS. IS-IS is an IGP used for routing within a single administrative domain. IS-IS is a Link state routing protocol and uses the SPF algorithm for comput...

OSPF Virtual-links vs GRE tunnels

OSPF Virtual-links vs GRE tunnels

Everyone who works in networking knows that every area in the OSPF domain must be connected to the backbone area (Area0). The reason behind this constrain is explained here. However it may be difficult for some reason to physically connect ...

Connected Routes Advertisment

Connected Routes Advertisment

What is considered as a connected route in the routing table ? An interface is configured with an IP address and mask,the configured subnet is installed as connected in the routing table. A static route is configured with only an ou...

distribute-list gateway with OSPF

distribute-list gateway with OSPF

The following example is showing how to use distribute-list with the gateway option for inbound route filtering  in OSPF. The diagram below shows R1 directly connected to R2 with OSPF configured between them. Initial Configuration: ...

BGP Default-Originate insights

BGP Default-Originate insights

BGP has multiple ways of advertising a default route to its neighbors;  the neighbor default-originate command is one of these methods and used to advertise a default route to a specific neighbor. Below are some characteristics of the defau...

Per packet vs Per destination load balancing

Per packet vs Per destination load balancing

Per packet load balancing: This method allows traffic distribution on a round robin fashion as stated in the previous post, this means that With per-packet load balancing enabled, the router sends one packet for destinationA over the fir...

Load balancing in a nutshell

Load balancing in a nutshell

Load balancing is the action of distributing traffic over multiple paths. The router automatically load balances traffic if it has multiple routes to the same destination in the routing table. RIP, OSPF and ISIS supports only equal cost ...

Inter-AS MPLS VPN - The whole story (1)

Inter-AS MPLS VPN - The whole story (1)

The IETF released the first RFC for MPLS L3VPNs; RFC 2547, “BGP/MPLS VPNs” in 1999 as a standardized form for the emerging Cisco’s tag switching at that time, succeeded with revised drafts in 2003, 2004 and 2005; draft-ietf-2547bis, mainly ...

System MTU explained

System MTU explained

By default any interface on the switch can only send or receive a frame of a maximum size 1500 byte. Some applications like (QinQ, MPLS over Ethernet) require increasing the MTU of the switches in your network to allow greater sizes because...

What is: a voice VLAN port?

What is: a voice VLAN port?

A voice VLAN port is an access port attached to a Cisco IP Phone, configured to use one VLAN for voice traffic and another VLAN for data traffic from a device attached to the phone. This feature allows the switch to use CDP for sending con...

Frame-relay Discard Eligibility Bit (DE)

Frame-relay Discard Eligibility Bit (DE)

What is the DE bit ? The DE bit is used to indicate that the frame has a lower importance than other frames and should be dropped first if the network experienced congestion. How to set the DE bit? We can use a simple network to te...

Frame-relay traffic shaping using MQC

Frame-relay traffic shaping using MQC

To apply frame-relay traffic shaping using a normal map-class, the command frame-relay traffic-shaping must be applied to the main interface. This method has a pitfall; the problem is that when you apply the frame-relay traffic-shaping c...

Understanding BGP communities

Understanding BGP communities

What are BGP communities? The BGP community attribute is a numerical value that can be assigned to a specific prefix and advertised to other neighbors. When the neighbor receives the prefix it will examine the community value and take pr...

How-to:Configure RIP route summarization

How-to:Configure RIP route summarization

In the following example I am going to show you how to configure route summarization under RIP using two methods. Our topology is shown below: R1 routing table before implementing summarization: R1(config-router)#do sh ip route rip ...

EIGRP metric manipulation

EIGRP metric manipulation

EIGRP is the most complex metric between all routing protocols metrics, in this post we are trying to clear the calculation of this metric as much as possible. Lets begin.. EGIRP metric is a composite metric made up of 5 parameters liste...

EIGRP timers (hello, hold and active)

EIGRP timers (hello, hold and active)

Today at work I have run into troubleshooting an EIGRP problem with one of our customers; while troubleshooting this problem I started making every optimization I know about EIGRP. In this post I am sharing with you EIGRP timers I adjusted ...

What is: BPDU filter?

What is: BPDU filter?

BPDUs are the messages exchanged between switches to calculate the spanning tree topology. BPDU filter is a feature used to filter sending or receiving BPDUs on a switchport. It is extremely useful on those ports which are configured as...

BGP helicopter view

BGP helicopter view

If you ask someone some simple BGP questions, like why do iBGP peers need to be fully meshed, and does this have anything to do with Synchronization, and do we need to run BGP on all the network routers, and so on, you can get him into the ...

Network Design Evaluation

Network Design Evaluation

Any Network that is well designed should satisfy the characteristics listed below: Network uptime: Any network should be designed to be up all the time, this means that you have to understand your network and what failures may affect th...

What is: AToM Control-Word?

What is: AToM Control-Word?

In the Layer 2 circuit IETF drafts, the control word is optional for most Layer 2 protocols, except Frame Relay and ATM AAL5 where it is required, The control word is 32-bit that is inserted between the VC label and the transported layer 2 ...

Prefix-list dilemma

Prefix-list dilemma

I've personally seen and experienced how playing with prefix-lists can be a mess, so let me try to break it down to simple pieces and then see how we collect these pieces together to have our required behavior. A normal access-list CANNO...

OSPF DR/BDR Election Myth

OSPF DR/BDR Election Myth

OSPF DR/BDR election process is something that is full of many details, i hope that in the following thread i can cover its main aspects. Each multi-access segment (ex: Ethernet Segment), will have 1 DR and 1 BDR. Each router on the segm...

OSPF RID Story

OSPF RID Story

Understanding the need for OSPF RID and how to control it is indeed a very important aspect to take care of when dealing with OSPF. The RID is a dotted decimal value used by OSPF routers to identify the other OSPF routers. Beside being u...

Unicast Reverse Path Forwarding

Unicast Reverse Path Forwarding

In order for a router to perform its function of forwarding packets it only needs to look at the destination address of the IP packet and never at the source; this allows an attacker to send malformed IP packets using spoofed source IP addr...

How OSPF selects best routes

How OSPF selects best routes

It is known for all of us that when two routes are received from the same routing protocol, the route with the lowest metric will be selected and installed in the routing table. In OSPF this is only true when the two routes are of the sa...

How-to: Avoid DNS lookup when mistyping a command

How-to: Avoid DNS lookup when mistyping a command

If domain lookup is enabled (default) the router treats each mistyped command as a hostname and tries to resolve its IP address by querying the DNS server. This behavior is undesirable in most cases because it wastes network administrato...

How-to: Configure Private VLANs

How-to: Configure Private VLANs

This is a master piece post from Petr Lapukhov explaining Private VLANs; what are they ? and how to configure and troubleshoot them ?. I am sure you will never get confused by Private VLANs anymore. Private VLANs revisited Read and un...

How-to: Configure Spanning Tree Protocol Part3

How-to: Configure Spanning Tree Protocol Part3

After explaining how STP works to ensure your network is free of bridging loops in previous posts, we are going directly to a configuration example. We will use a simple topology in the diagram below and configure the switches to accomplish...

How-to: Configure Spanning tree protocol Part2

How-to: Configure Spanning tree protocol Part2

In the first post STP part1, we discussed the root bridge election process, that was the first step in calculating the spanning tree topology. Lets dive and explore step2. Step2: Best Path selection After choosing and agreeing on the ...

How-to: Configure spanning tree protocol (STP) Part1

How-to: Configure spanning tree protocol (STP) Part1

// As we mentioned in one of our previous posts, STP was develope...

Spanning Tree the problem and the solution

Spanning Tree the problem and the solution

Spanning tree protocol or STP is used to provide redundant links in the network while preventing the danger of bridging loops. Our network below has two switches connected to each other by two FastEthernet links for redundancy. In such s...

Etherchannel load balancing case study

Etherchannel load balancing case study

Etherchannel is a very effective feature that provides redundancy and load distribution within your switching network. However failing to choose the right load distribution algorithm my leave you under utilizing your network resources. ...

How-to:Configure BGP aggregation Part2

How-to:Configure BGP aggregation Part2

In the first post we explored the basic configuration of BGP route aggregation with and without the summary-only keyword. In todays post our task is to explore the suppress-map keyword using the same topology used in the first post. "pl...

What is: extended VLAN range?

What is: extended VLAN range?

Extended VLANs are VLANs within the range of 1006 to 4094. They are mainly used in service provider networks to allow the provisioning of number of customers. In order to configure an extended VLAN you have to follow the guideline below: ...

How-to: Configure trunk VLAN allowed list?

How-to: Configure trunk VLAN allowed list?

By default all VLANs configured on a switch are allowed over all trunking interfaces. Sometimes you need to change the allowed list over a specific trunk. When a VLAN is allowed on a trunk, traffic coming from interfaces belonging to this V...

How routers select best routes ?

How routers select best routes ?

Routers select best routes based on the following criteria: Longest prefix match: Routers select routes with the longest match to the destination address in the forwarded packet. For example if a packet is destined to 192.168.12.1 and t...

What is: IP unnumbered?

What is: IP unnumbered?

IP unnumbered is method that you can use to enable IP processing on a Point to Point interface without assigning an it an IP address to conserve the IP address space. All you need to do, is to select an interface that you are going to bo...

How-to:Configure PPP authentication Part2 (CHAP)

How-to:Configure PPP authentication Part2 (CHAP)

The second and the most secure authentication method in PPP is CHAP. CHAP stands for challenge Handshake Authentication Protocol. How CHAP works? If CHAP is negotiated successfully during the LCP phase, the authenticator sends a chall...

How-to: Configure PPP authentication Part1 (PAP)

How-to: Configure PPP authentication Part1 (PAP)

PPP has two different authentication methods, in today's post we are going to explore the first method which is PAP. PAP stands for Password Authentication Protocol which is a simple authentication method. PAP is considered an insecure m...

The ip route-cache command - Bury the hatchet series

The ip route-cache command - Bury the hatchet series

From what I've seen in the practical life, this command puzzles many people, i hope to cover it throughly. Controlling the packet switching method depends upon which method we are talking about, in the case of CEF Switching its all about...

PPP in brief

PPP in brief

The Point-to-Point Protocol (PPP) provides a standard method for transporting multi-protocol packets over point-to-point links between two peers. In order to establish a communication link between two peers, each end of the PPP link must...

What is a virtual template/access interface?

What is a virtual template/access interface?

What is a virtual-template interface? A virtual-template interface is a logical entity that can be used to apply predefined interface configurations for virtual-access interfaces. Virtual template interfaces is configured independentl...

Passive-interface command behavior in RIP, EIGRP & OSPF

Passive-interface command behavior in RIP, EIGRP & OSPF

Passive-interface command is used in all routing protocols to disable sending updates out from a specific interface. However the command behavior varies from o­ne protocol to another. In RIP this command will disable sending multicast up...

How-TO: Configure DHCP on a CISCO router

How-TO: Configure DHCP on a CISCO router

This post is about configuring a CISCO router to act as a DHCP server in your network. Task1: Configure R1 to act as a DHCP server and provide all network information to hosts in the LAN dynamically. (R1 and R2 are directly connected via...

CAR - Rate limit examples

CAR - Rate limit examples

CAR is a policing mechanism used to limit the transmission rate of some traffic flow. Cisco actually recommends using MQC policing for its modularity and features, but CAR is still used widely in most operational networks for its simplici...

Automatic summarization in RIP and EIGRP

Automatic summarization in RIP and EIGRP

Summarization in RIP and EIGRP can be configured manually using the ip summary-address command or automatically using auto-summary command. when auto summarization is in effect routers behave as shown in the steps below: Subnets are s...

How-to: Configure Frame-relay Switching

How-to: Configure Frame-relay Switching

Routers can be configured as Frame Relay switches to be used mostly in service provider or LAB environments. Lets see how you can configure frame-relay switch to use your in studies. On a Frame Relay switch, frames from a Frame Relay PVC...

Limiting non-business related applications during work hours

Limiting non-business related applications during work hours

In this post we will explore how to limit or even stop your employees from using applications that are not related to the business during work hours. In the following example I am going to use HTTP as an example for unwanted applicatio...

OSPF cost calculation pitfall with high bandwidth interfaces

OSPF cost calculation pitfall with high bandwidth interfaces

Cisco is using the (Reference bandwidth/interface Bandwidth) formula to calculate OSPF cost values of different interfaces; where the reference bandwidth is 10^8 by default. Using this given formula the cost of FastEthernet links would...

How-to: Configure trunking

How-to: Configure trunking

A trunk port is a layer 2 port that may carry traffic from multiple VLANs. Trunk ports are mostly used to connect two switches, switch and a router for inter-vlan routing or a server. Cisco switches support two types of trunking encapsul...

VTP in brief

VTP in brief

VTP is a Cisco proprietary protocol used in switching environment to reduce the administrative overhead of managing VLANs configuration.Lets explore how VTP can reduce VLAN management tasks by the following example: Assuming that you hav...

How to Configure Frame-relay interfaces

How to Configure Frame-relay interfaces

Frame relay interfaces can be configured as Physical, Multipoint and point-to-point interfaces. Frame relay routing protocols and mostly all network configuration is heavily affected by interface type selected. In the following digram...

How-to:Configure BGP aggregation Part1

How-to:Configure BGP aggregation Part1

In this series we will explore how route aggregation is accomplished in BGP, We am going to split this topic into multiple posts in order to keep things simple and manageable. Our Network is shown in the digram below. R1 is directly co...

BGP fast-external-fallover

Routers' Operating systems

Routers' Operating systems

The router operating system is a piece of software responsible for managing the router resources by controlling and allocating memory, prioritizing system requests and processes, controlling I/O devices and managing file systems. The mos...

What is a Native VLAN?

What is a Native VLAN?

Native VLAN is a dot1Q concept that was created for backward compatibility with old devices that don't support VLANs. Full story detailed below.. How Native VLAN works? Frames belonging to the native VLAN are not tagged when sent out...

PBR as a QOS tool

PBR as a QOS tool

In order to apply QOS policies in your network, traffic should be classified first. There are many techniques available for packet classification. PBR is one of these techniques as discussed below. PBR can be used to match a specific flo...

Routers' Memory types

Routers' Memory types

The memory come in many forms for several storage purposes such as to store the operating system , the configuration, the bootstrap, packets, and so forth. Below is a detailed description of all memory types used in routers and the purpose ...

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