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....
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. ...
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. ...
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...
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...
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 ...
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...
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...
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 ...
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...
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...
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...
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...
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...
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...
A quick example for find the difference in days between two dates in python using the datetime standard library package....
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.ÃÂ Out of lazines...
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...
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...
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....
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...
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...
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 ...
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 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...
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...
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...
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....
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 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...
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 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...
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 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...
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...
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...
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 ...
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...
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 ...
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...
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...
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...
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...
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 ...
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 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...
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...
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 ...
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 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...
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...
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 ...
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...
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...
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 ...
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...
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...
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 ...
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...
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...
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...
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...
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? 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...
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 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...
The internet growth is awesome, day by day people recognizes howÃÂÃÂ internet is important in their daily personalÃÂÃÂ and business life and even for their culture, so the internet has a good bit of newbie everyday which depleted some internet re...
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...
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 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...
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 ...
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...
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...
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 ...
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...
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...
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...
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...
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...
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...
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...
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...
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 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 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 ...
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...
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...
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 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...
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...
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...
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...
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 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 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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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'...
Guys, I would like to share with you the real description of the Network Architect job. Enjoy reading...
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 ...
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...
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...
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...
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...
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...
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...
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...
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 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...
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 ...
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...
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 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 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 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 ...
The IETF released the first RFC for MPLS L3VPNs; RFC 2547, âBGP/MPLS VPNsâ in 1999 as a standardized form for the emerging Ciscoâs tag switching at that time, succeeded with revised drafts in 2003, 2004 and 2005; draft-ietf-2547bis, mainly ...
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...
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...
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...
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...
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...
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 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...
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 ...
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...
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 ...
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...
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 ...
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 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...
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...
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...
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...
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...
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...
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...
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 ...
// As we mentioned in one of our previous posts, STP was develope...
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 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. ...
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...
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: ...
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...
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...
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...
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...
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...
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...
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 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 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...
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 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...
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...
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...
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...
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...
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 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...
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...
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...
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...
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...
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...
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 ...
