Total 43 Blogs

Created by - Orhan Ergun

What is CDN - Content Delivery Networks?

Content Delivery Network companies replicate content caches close to a large user population. They don’t provide Internet access or transit service to the customers or ISPs but distribute the content of the content providers. Today, many Internet Service Providers started their own CDN businesses as well. An example is Level 3. Level 3 provides its CDN services from its POP locations which are spread all over the World. Content distribution networks reduce latency and increase service resilience (Content is replicated to more than one location). More popular contents are cached locally and the least popular ones can be served from the origin Why CDN - Content Delivery Networks are necessary? Before CDNs, the contents were served from the source locations which increased latency, thus reducing throughput. Contents were delivered from the central site. User requests were reaching the central site where the source was located.Figure 1 - Before CDN With CDN Technology, the Contents are distributed to the local sites. Figure 2 - After CDN   Amazon, Akamai, Limelight, Fastly, and Cloudflare are the largest CDN providers which provide services to different content providers all over the world. Also, some major content providers such as Google, Facebook, Netflix, etc. prefer to build their own CDN infrastructures and become large CDN providers. CDN providers have servers all around the world. These servers are located Inside the Service Provider networks and the Internet Exchange Points. They have thousands of servers and they serve a huge amount of Internet content. CDNs are highly distributed platforms. As mentioned before, Akamai is one of the Content Delivery Networks. The number of servers, number of countries, daily transactions, and more information about Akamai’s Content Distribution Network are as follows: 150.000 servers Located in 92 countries around the world Delivers over 2 trillion Internet interactions daily Delivers approximately 30% of all Web traffic Their customers include: All top 20 global eCommerce sites, top 30 media companies, 7 of the top 10 banks, 9 of the largest newspapers, 9 out of 10 top social media sites  

Published - Tue, 24 May 2022

Created by - Orhan Ergun

What is IP Anycast? Where it is used in networking?

What is IP Anycast? Is IP Anycast a routing protocol? Where IP Anycast is used in Networking?. In this post, I will answer these questions. I discuss these questions and often ask them in my training as well. I always receive many different answers but you will see how it is easy to understand the idea behind anycast after reading this post. IP Anycast is a way of assigning IP addresses. The same IP address is assigned to multiple nodes. It is not a routing protocol, switching protocol, or a special network design. Just a way of assigning an IP address. There are many use cases for it. Internally in the networks, Multicast uses IP Anycast for load balancing and redundancy. Specifically, PIM ASM (Protocol Independent Multicast - Any Source Multicast) uses IP Anycast for the RP (Rendezvous Point) address assignment. The same IP address is assigned on multiple nodes in the network and the underlying IGP protocol shortest path is used to determine the closest RP in a topology. IP Anycast for  CDN (Content Delivery Networks) IP Anycast is a special method for request routing in CDN architecture. Let's have a look at what is request routing and how Anycast is used in request routing. Request routing or also known as server redirection is a method to bring the customer to the optimal server in a CDN architecture.   Figure - IP Anycast vs. Unicast   In this approach, the same IP address is assigned to multiple servers located in a distributed manner. When the client sends requests to the IP address, the requests will be routed to the nearest server defined by the routing policy. With this approach content providers may lose some server selection flexibility. Consider a scenario in which Anycast forwards requests to the nearest (yet overloaded) server, by simply respecting a distance-based routing policy. CDN service providers who configure their platform with Anycast set a single IP address for all their nodes! Unlike a DNS Based CDN Redirection, where every node has a unique IP address and recursive DNS routes the client to the closest node, it uses the Border Gateway Protocol (BGP) to route clients using the natural network flow of the Internet BGP is a network-level protocol that is used by Internet edge routers to exchange routing and reachability information so that every node on the network, even though it is autonomous, knows the state of its closest network neighbors. Anycast uses this information to efficiently route traffic based on hop count ensuring the shortest traveling distance between the client and its final destination.

Published - Mon, 11 Apr 2022

Created by - Orhan Ergun

Why MPLS used? 3 things you have to know!

Why MPLS is used for?. A very common question among IT Engineers. What are the common use cases of MPLS - Multi-Protocol Label Switching?  MPLS Use Cases When it is first invented, 20+ years ago, it was considered one of the most scalable ways of doing VPNs. Faster packet processing could be achieved compared to IP destination-based routing because the IP address was 32 bits long but the Labels are just 20 bits long. But, quickly after the first invention purpose, MPLS VPNs became the most dominant reason for Networks to deploy MPLS - Multiprotocol Label Switching technology. It supported Ethernet over MPLS - EoMPLS, which is known as Point to Point Layer 2 MPLS VPN, and then soon after VPLS, which is Virtual Private Lan Service, vendors started to support. VPLS is any to any, or also known as many to many technologies. It means you can connect. your multiple sites in Layer 2 and extend IP subnet by using VPLS technology. It works based on a full mesh of Pseudowires. After Pseuodowire based Layer 2 VPNs, MPLS actual boom happened with MPLS Layer 3 VPNs. With MPLS Layer 3 VPN, which is also known as Peer-to-Peer VPN, MPLS CE, and MPLS PE, setup routing protocol neighborship and IP address prefixes are advertised from the CE to PE and between the PE as end-goal being reachability between the CE devices end-to-end. MPLS VPN PE-CE protocols should be known well by the way and we have blog posts on the website for it.MPLS Layer 2 and MPLS Layer 3 VPN has been used for the most common reason for MPLS and as of 2022, MPLS VPN is the most common use case for network owners to deploy MPLS technology. But recent years, we started to see EVPN technology and its adoption. It quickly became mature and many networks, at least for the last 5 - 6 years have been deploying it. It supports both Layer 2 and Layer 3 MPLS VPNs, though initially it was invented for the MPLS Layer 2 VPN. Other than VPNs, MPLS Traffic Engineering, Carrier Supporting Carrier, Seamless MPLS, and MPLS Transport Profile are some of the architectures, mechanisms, network administrators deploy to get the advantage of.We just provided a hyperlink, just click on the words to open a blog post about any particular technology. Don't forget, if technology doesn't come up with business benefits, we shouldn't deploy it.

Published - Mon, 11 Apr 2022

Created by - Orhan Ergun

Understanding CGN - Carrier Grade NAT

Carrier-Grade NAT (CGN) is also known as LSN (Large Scale NAT). And in my opinion, it should be called LSN since there is nothing for CGN to be a carrier-grade. It is just a NAT. With CGN, Service Providers do NAT44 on the CPE from a private address to another private address (Well known /10 prefix which is allocated by IANA) and another NAT44 on the Service Provider network. That’s why you can hear CGN, LSN, Double NAT, or NAT444. All of them refer to the same thing. Carrier-Grade NAT CGN and so many IPv6 topics are covered in great detail in my IPv6 Zero to Hero Course. But with CGN you are not enabling IPv6. CGN is a way to solve the IPv4 depletion problem in a very problematic way. Companies are also using trade-market to purchase IPv4 public addresses. The average cost per IPv4 address is around 8-10$ currently. This might increase over time. And it would be wise to expect to see much bigger DFZ space by the time because of de-aggregation. With CGN, IPv4 private addresses are shared among many customers and those shared addresses are NATed at the CGN node twice.   Difference between Customer NAT (Residential NAT) and SP NAT (CGN, LSN) With Residential NAT, a single public IPv4 address represents one household, with SP NAT (CGN, LSN), a single public IPv4 address is shared across multiple households With Residential NAT, 16-bit port space(65000 TCP and UDP ports) is for a single household but with SP NAT, 16-bit port space of the IP address is shared among multiple households. CGN can be deployed either Inline or Offline. Inline CGN deployment is more common in Enterprise and Residential networks as network traffic pass through the NAT box. Offline CGN removes the NAT from the primary data path and utilizes source routing mechanisms to send the traffic to the NAT boxes. Offline CGN is a more common deployment model in the SP networks Carrier-Grade NAT - CGN Advantages It is well known NAT, two times NAT operation, customer and SP side, no IPv6 learning curve CPE – Customer NAT doesn’t need to change CPE doesn’t need to support IPv6 Carrier-Grade NAT - CGN Disadvantages CGN is an IP address sharing solution, many users share the same Public IP address, there are problems with it Some applications break, applications that can work with a single layer of NAT may not work with two layers of NAT Sharing addresses makes operations/troubleshooting harder  How many ports should be assigned to each user? It is called Port Spray Many websites open 80-100 TCP connections (Newspapers), and some apps open hundreds of sessions (Google Map, etc.) Intense logging will be needed for the Lawful intercept Traceability of users behind Carrier-Grade NAT CGN CGN in forwarding path (Inline deployment) becomes a single point of failure Offline CGN deployment requires source routing which creates unnecessary complexity CGN IP address getting blacklisted due to address sharing (Not every user is innocent)

Published - Sun, 10 Apr 2022

Created by - Orhan Ergun

Broadband Network Architecture – Access Network Models

Broadband Network - There are many broadband services Service Providers offer to their customers today. As a network engineer, you need to know the most common services and their advantages, disadvantages, design characteristics, and so on. To have a great understanding of SP Networks, you can check my SP Workshop and also my newly published “Service Provider Networks Design and Perspective” Book. The Book covers the SP network in great detail. In this post, I will introduce these services and if I can see interest from the readers, I will explain the design aspects and deployment models of each one of them. Note: I am going to explain broadband services in this post, not baseband, we are in 2022 right?   Access network infrastructure connects the backbone network to the customers.   There are two groups of broadband access technologies. Fixed broadband technologies and Mobile Broadband technologies. You can find many Mobile Broadband articles on the website. Figure 1: Access Network Technologies and the associated infrastructures I will explain these technologies and then I will cover how physical locations can be connected to Fixed Broadband and Mobile Broadband infrastructure. Fixed Broadband Technologies Fixed broadband refers to those technologies where the end-user must remain at the same location to use the broadband service. The access network is associated with a specific physical location. Fixed broadband can be provided by wireline, wireless, or satellite technologies. Wireline Fixed Broadband Wireline fixed broadband service can be received in many ways as well. 1. DSL Fixed Wireline Broadband Traditional xDSL (ADSL, VDSL, etc.) service is one way of having fixed wireline broadband service. Today in many continents most common access network technology is DSL.   Figure 2: DSL deployment and the components   In DSL access, the traditional copper line of the telephone network is equipped with digital subscriber line technology. DSLAM is used at the Service Provider network and the customer modem connection is terminated at the DSLAM. 2. Cable Fixed Wireline Broadband The second fixed wireline broadband access technology is Cable Broadband. Broadband service is received through cable access by upgrading traditional cable television networks. Customers can receive both broadband Internet service as well as TV service over the same cable. Figure 3: Cable Broadband simplified architecture 3. Fiber Fixed Wireline Broadband The third and last fixed broadband access technology is Fiber. You probably heard FTTx before. There are many deployment options for FTTX access for sure. You may have heard FTTH (Fiber to the home), FTTP (Fiber to the Premise), FTTB (Fiber to the Building), and so on. Figure 4: Different FTTx Deployment Options Fiber access infrastructure is different from DSL and Cable in many ways. With Fiber to the Home, from the fiber termination device of the Service Provider up to the modem in the customer's home, the entire access network is fiber. This is the fastest option customer can get. As you might know, finer has much less attenuation and loss compared to copper and coaxial cable. Much higher data rates can be achievable through fiber. (In theory, you can send 300.000km/s over fiber, because the limit is the speed of light). Between the customer and the street cabinet can be copper-based and DSLAM can be located on the street. DSLAM to the fiber termination device which is located at the Service Provider Telephone Exchange (In the U.S it is generally called CO (Central Office) ) can be fiber. This is another way of deploying FTTx service and called Fiber to the Premises/Cabinet or Curb. In the above figure, the third deployment model which is Fiber to the Building is shown. In this deployment option, fiber is brought up to the building and between DSLAM and the customer modem, the connection is copper-based. Wireless Fixed Broadband The most common technology for fixed wireless is WiMAX (Worldwide Interoperability for Microwave Access). Microwave access is much cheaper compare to fiber access for wireless access operators. Fiber access infrastructure can be leased from the fiber infrastructure providers by the wireless operator (This is very common among the Mobile Service Providers) or the wireless operators can deploy their own fiber infrastructure. In both methods, capital expenditure is higher compared to wireless-based access systems. Thus, today's most common wireless backhaul is deployed via microwave as you can see from the below picture as well.   Figure 5: Fixed Wireless Network With WiMAX, access speed can reach up to 1Gbps and the customer connection speeds depend on the distance from the wireless base station. Satellite Fixed Broadband Satellite connections are generally used in rural areas where there are no other access network options available. By the way, when you work in the Network Operator or Service Provider environment, especially if you are doing any kind of capacity planning work (Transport, Access, or IP network), you always hear urban, sub-urban, metro, and rural areas. These are related to the number of people per square kilometer. If the area is so crowded (Generally 4000 people/ sq km) it is called metro, after metro, urban, then sub-urban, least crowded places are called rural areas. Satellite connection has much higher latency compared to other fixed broadband access technologies. Speed increases by reducing latency, increasing bandwidth doesn’t mean faster connection. This is another long discussion probably we should make. When people increase their bandwidth, they tend to say we have a faster connection. That's completely wrong. When you have a shortcut (so lower latency ) you have a faster connection. satellite connection   Figure 6: Satellite Communication Last but not least, satellite connection is almost always more expensive for the same speed, compared to other fixed broadband access technologies. Mobile Broadband Mobile broadband refers to those technologies where the end-user can use the broadband service while on the move and from any physical location. These technologies provide different service speeds to the customers and the Service Provider access and the backbone infrastructure is designed in a completely different way.     Figure 7: Different mobile broadband connection speeds As I told you in the beginning, we have many mobile broadband technology posts on the website and you can watch the Mobile Broadband Technologies webinar which I did with one of the mobile broadband experts worldwide earlier this year. Fixed broadband technologies due to technical and financial aspects, tend to be prevalent in highly populated areas (Metro, Urban ) and mobile broadband technologies are more prevalent in less densely populated places. (Rural areas). If you liked this post, share it on social media and put a comment in the comment box below so I know that there is an interest in these technologies among my readers.

Published - Sun, 10 Apr 2022

Created by - Orhan Ergun

Unicast Multicast Broadcast Anycast and Incast Traffic Types

Unicast Multicast Broadcast Anycast and Incast Traffic Types will be explained in this post. Traffic flow/traffic types are important information that needs to be considered in Network Design, thus understanding each one of them by every IT Engineer is critical and Important for Application requirements, Security, and Performance of the overall system. In this blog post, Unicast, Multicast, Broadcast, and Anycast traffic types/patterns will be explained with examples and the topologies. Unicast Traffic Flow Unicast traffic type is a point-to-point communication type. Usually from a scalability perspective, Unicast is not the desired traffic type. But if there are only two points that communicate with each other, Unicast is an optimal choice. Multicast Traffic Flow Point to Multipoint or Multi-Point to Multi-Point Traffic type. If the communication is targeted to a group of recipients, then the Multicast traffic type is more suitable. Multicast source/sender, receivers, and multicast groups are the components of Multicast communication. A classical example is IPTV - IP Television. One multicast group is assigned for each IPTV channel and only interested receivers get the stream. Broadcast Traffic Flow If traffic is sent to everyone, regardless of considering if there is an uninterested receiver, then it is a broadcast traffic type. ARP traffic is a classical example of Broadcast traffic type. ARP - Address Resolution Protocol packets are sent to the broadcast address and every receiver has to process it, even if the packet is not targeted for them. If there are many uninterested receivers, Broadcast traffic is considered inefficient. Anycast Traffic Flow Anycast is a way of deploying an IP address. The same IP with the same subnet mask is assigned to multiple devices and whichever other devices need to communicate with this IP address, send the traffic to the topologically (IGP/BGP cost) closest point. Classical examples are, Anycast DNS such as Google DNS or Multicast Anycast RP (Rendezvous Point). Incast Traffic Flow If the traffic type is Multipoint to Point, it is called Incast. Big Data type of traffic requires many servers to process the same data and send the output to another engine. So multiple servers compute the information and send it to the receiver at once. Network design is so critical as there might be bottlenecks easily in this type of traffic. Unicast vs Multicast The difference between unicast and multicast, as mentioned before, if there are multiple receivers, sending traffic as unicast would be inefficient. If the packet is sent only once from the source, and the network can replicate it, less effort is spent on the source, and less bandwidth is used on the network. Let's have. a look at the below example: There is one sender/source but 3 receivers, so in Unicast's case, the same data needs to be sent 3 times. In Multicast communication, the sender/source sends the data only 1 time, network devices replicate the traffic, and 3 receivers get the same data. Obviously, this is more optimal for the sender and network resources, because of less resource usage. These resources usually are CPU, Memory, and Network Bandwidth. Multicast vs Anycast Multicast traffic is sent to many receivers at the same time. So, the source/sender sends one copy and it can be sent to hundreds, if not thousands of receivers, and all receivers get it. Anycast on the other side, one copy is sent and there is one receiver as well. But if that receiver fails, there is another receiver with the same IP and same subnet mask in the network and it receives it. So, with anycast target/receiver is always more than one. In the Google DNS case, with the same IP address, there are tens of DNS servers around the world. If traffic comes from France, the France DNS server replies, if it comes from London, London DNS replies, and so on. Closest receiver/target replies. Multicast vs Broadcast An important difference between Multicast and Broadcast is, that with Multicast we send the traffic to the interested receivers. With broadcast we don't care if there is interested people or not, it is sent everywhere continuously. There is Multicast PIM Dense mode, for example, you might compare it with Broadcast. They can be seen as similar but they are not. With PIM Dense, we send the traffic everywhere initially but if there are no interested receivers at the same Multicast enabled locations, the sender stops sending to those locations because the sender receives Multicast Prune messages. With broadcast, no Prune mechanism, thus traffic is sent continuously even if there is no interested receiver. Unicast vs Multicast vs Broadcast vs Anycast When you see this comparison again, just remember, if it is only two-party for communication, Unicast is an optimal choice. If there are multiple, look at if some of them are interested to hear some discussion, others might be interested in other discussions, then Multicast is the best. If there is only one type of discussion and everyone should receive it, the broadcast is the optimal choice. Let's say a group of people in a party some of them talk about politics, other groups of people discuss religion, and so on. So this is Multicast communication. But if someone in that party loudly starts shouting and everyone has to hear even if they are uninterested, he is broadcasting. In a summary: Unicast is one-to-one, Multicast is One to Many, Broadcast is One to All, Anycast is One to Any and Incast is Many to One communication models.  Source: www.researchgate.com  

Published - Sat, 09 Apr 2022

Created by - Orhan Ergun

What is Storm Control?

Storm control is a feature for monitoring traffic levels and dropping broadcast, multicast, and unknown unicast packets, which is commonly known as BUM Traffic, and when a specified traffic level, referred to as the storm control level or storm control bandwidth is exceeded, limiting the traffic to protect the Local Area Network environment. In this blog post, we will try to understand the basics of it. Storm Control Broadcast LevelAlthough the Storm Control feature is mainly used for Broadcast, we should configure it to protect from unnecessarily used Multicast and Unknown Unicast packets. There can be bugs in the software or hardware or due to the mis-cabling or configuration, if any of the above traffic exceeds the limit that we specify, traffic should be blocked. We need to understand some terminologies if we want to understand Storm control and its usage on Network Switch. In the above configuration, we will show not only for Broadcast but also for Multicast and Unknown Unicast threshold levels on the Cisco switches. Cisco Storm Control Let's have a look at how Storm Control is used in Cisco switch and let's learn some new terminologies. interface GigabitEthernet0/0 storm-control broadcast level bps 100k 90k storm-control multicast level pps 50 30 storm-control unicast level 1.00 0.50 On the above configuration, the below parameters are used. Let's briefly define each one of them. broadcast—Configure broadcast storm control. multicast—Configure multicast storm control. unicast—Configure unknown unicast storm control. level—Specifies the threshold levels for broadcast, multicast, or unicast traffic. rising_threshold—Upper threshold level. falling_threshold—Lower threshold level. bps—Specifies the suppression level in bits per second. PPS—Specifies the suppression level in packets per second --The rising threshold is the traffic limit after which, that particular traffic is blocked. --The falling threshold is the traffic limit below which, that particular starts forwarding again if it was already blocked For the broadcast traffic then, on the above config, we specify 100k as Rising_threshold, 50k as falling_threshold value. Meaning at 100kbit/s traffic will be blocked when the traffic level falls under 90kbit/s again. traffic will be forwarded. This feature is and should be used in real-life in the campus networks/local area networks, where you have a Layer 2 domain. When the Layer 2 domain gets larger, the importance of the Storm Control feature increases as well. You can find more information on Layer 2 network design, in our Layer2 Network Design Course.

Published - Thu, 31 Mar 2022

Created by - Orhan Ergun

What is KISS Principle ? Keep it Simple and Stupid ?

What is KISS Principle ? Okay it stands for Keep it Simple and Stupid but what does really it mean in networking ? Can we really make things simpler ?. Probably yes but should we ? Let’s remember What Einstein said about simplicity.   ” Everything should be made as simple as possible, but no simpler ”   It is very long debate what really Einstein was trying to say and unfortunately since He is dead, we can’t ask himself but at least let’s try to understand.   If ‘A represents a process, and ‘A***’ represents the simplest possible version of ‘A’, then one should work towards finding ‘A***’, and not towards an intermediate version ‘A**’ or ‘A*. From this example, as you can understand, most possible simplicity is recommended by Einstein. How we can adapt Einstein’s simplicity principle to networking ? Let’s think about routing protocols.In a small OSPF network, imagine you have 1 datacenter and 20 branch offices. And totally you have 22 routers, 2 in DC and 1 in each branch office.   Let me give you design options.   1. You can deploy in datacenter and each and every branch , different OSPF processes, and you deal with the redistribution because you use different OSPF processes in different places of network 2. You can place datacenter in OSPF Backbone area and each and every branch in separate Area, you deal with multiple areas, 21 different OSPF area in this case 3. You can place datacenter in OSPF Backbone area and all branches in same non-backbone area. You have totally two OSPF areas and 2 ABRs. 4. You can place datacenter and all the branch offices in a backbone area. No multiple OSPF area , No ABR   First option is most complex and it is unnecessarily complex. Second option is less complex than third one and fourth option is the least complex. In other word, fourth option is simplest option.   Of course, complexity is necessary in some cases to solve particular problem as I explained in my ‘Network Complexity’ article, for the above requirements (1 DC , 20 branches, 22 routers), it is best to place all routers in one backbone area.   KISS Principle recommend the same what Einstein is recommending with his quote and goes beyond.   Keep it simple part of the KISS principle has the same meaning with Einstein’s quote.   Stupid part comes from the idea of having dump core devices and smart edge devices.   In fact, I wrote an article on the subject and highlighted that ‘Edge devices are the brain of the network’   Remember in three layer architecture , access , aggregation and core. What was the job of each layer ? Access layer is used for user/device termination , policy enforcement , trust boundary, filtering and so on. Aggregation layer is used speed multiplexing , providing scalability for overall network by preventing excess amount of connection. Core layer is used to pass traffic between each and every point in the network , as fast as possible, if it is possible, without any policy enforcement.Of course, bigger size of networks (MNOs for example) use 4 even 5 layers as of 2017 but it doesn’t change the role of core/backbone layer.   Stupid part of KISS principle actually mean, keeping the intelligent functions away from core/backbone of the networks. As an example, in MPLS network, Core devices only swap the label, but edge devices runs MP-BGP, VRFs, layer 2protocols or Routing with the customers, QoS and security functions and so on.   What I see in the networking field, what most people do, is to read, watch materials on the topic , just modify it a little but and publish it as their own. Later on, after couple years another people research the same topic and repeat the same.   This goes on. But instead, if people think multiple steps ahead and design the things in the simple way possible, so no more modifications can be possible by anyone else in the future.   Keep it simple and Stupid is very important and you should remember this principle , Einstein, Stupid Core Networks and Orhan Ergun whenever you design any communication network.

Published - Wed, 16 Feb 2022

Created by - Orhan Ergun

ABR vs ASBR in OSPF

ABR vs ASBR in OSPF. If you are new to Network Engineering and you are learning Dynamic Routing Protocol from scratch, you want to understand the differences between ABR vs ASBR and if there are similarities you would like to learn those too. In this post, we will learn both similarities and differences. Let's first understand both of these terms. ABR is purely an OSPF terminology, but ASBR is not. In fact, the detailed post about ASBR and the usage of ASBR in Different Places of Networking is explained in our What is ASBR Blog post. ABR - Area Border Router is a device which is connecting two different OSPF Areas. One of those OSPF areas has to be Area 0, which is also known as Backbone Area.   In the above topology, R3 is an ABR, connecting Area 0 and Area 1, R4 is an ABR as well, connecting Area 0 and Area 2. R1 is referred to as Internal Backbone Roter as it doesn't have any other connection than Area 0, Backbone Area. In this topology, there is also an ASBR - Autonomous System Boundary Router. It is called ASBR because on that router external prefixes are injected into the Internal network. Can ABR be used as an ASBR?   On the above topology, as I indicated above, R3 and R4 are the ABR routers. Can we use ABR as an ASBR?. So, can we inject prefixes from the outside networks to our Internal network? Yes, we can. We can inject (Redistribute) prefixes on R3 and R4, ABR Routers to the Internal Network. Thus, similarity point of view, ABR and ASBR functions can be on the same device. The difference is, when you hear the ASBR term, that is a device you inject prefixes from other networks to your network and. ABR is a device that is connecting two Internal OSPF Areas. Hope it is very clear now.

Published - Mon, 14 Feb 2022