Total 248 Blogs

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

What is IRU? Indefeasible Right of Use?

If you are working in the Operator, Service Provider, or Telco/Carrier networks, you probably heard this term. If you haven't, you need to learn it. To have a great understanding of SP Networks, please check our 150 hours, detailed, CCIE SP Training Service Providers use the transport network of others. This is very common, in fact, even the biggest networks use other carriers' transport/transmission infrastructure, especially outside of their main location. For example, an operator might provide services mainly in the U.S, but want to extend its network to Europe. Instead of setup a fully-fledged telecom environment in Europe to provide a service, let's say to Business and Residential customers, one option is to use local carrier networks in Europe. Indefeasible Right of Use (IRU) Is a permanent contractual agreement That cannot be undone, between the owners of a cable and a customer of that cable system. The cable is mostly a fiber cable as fiber can carry more data than any other type of media. Buying a fiber can be in two ways, either, Leasing or IRU (Indefeasible Rights of Use) based. Indefeasible means ‘not capable of being voided or undone. The Customer purchases the right to use a certain amount of capacity of the fiber system for a specified number of years. Customer who purchases IRU can lease the capacity to other companies. Let me give you an analogy. Think of it in this way, if you are renting an apartment, you sign a contract with the Landlord as a tenant. You cannot rent that apartment to someone else. This is similar to leasing. But if you are the landlord, you can rent it to anyone you want. This is an example of an Indefeasible Right of Use-based agreement. Let's have a look at the differences between Leasing and IRU-based contracts in detail. There will be some technical terms, be ready. IRU vs. Leasing a Fiber IRU contracts are almost always long term such as 20 to 30 years (Cable lifetime is generally considered as 25 years) Leased fiber doesn't have to be a long term contract The most common leased service is IPLC which is Internal Private Leased Circuits. IPLC can be a half circuit or full circuit. (I will explain the half and full circuits IPLC in a separate post) IPLC unlike IRU doesn't dictate the buyers to pay the cost of fiber upfront, IPLC is not a prepaid service Leasing is very flexible (In terms of contract duration, speed option, etc.) but IRU can be very cost-effective Indefeasible Right of Use based contract gives the purchaser the right to use some capacity on a telecommunications cable system, including the right to lease that capacity to someone else But is an Indefeasible right of use-based contract suitable for every company? Why people don't buy if it has a cost advantage? Why bother with MPLS? Should smaller companies purchase an IRU-based fiber? Smaller companies that need a leased line between, say, London and New York do not buy an IRU. They lease capacity from a telecommunications company that themselves may lease a larger amount of capacity from another company (and so on), until at the end of the chain of contracts there is a company that has an IRU, or wholly owns a cable system. Buying an IRU compare to other types of circuits such as MPLS, Metro Ethernet and Internet is much more costly. Thus smaller companies generally don't buy IRU capacity.

Published - Sun, 10 Apr 2022

Created by - Orhan Ergun

Tier 1, Tier 2 and Tier 3 Service Providers

What is tier in the first place? If you are dealing with Service Provider networks, you hear this term a lot. But how do we define Tier 1, Tier 2, and Tier 3 Service Providers? I am explaining this topic in deep detail in my specialized BGP Zero to Hero course. What should be their infrastructure to be seen as Tier 1 for example? Which tier is bigger in scale? Which one is better for the customers to purchase a service from? Why do Service Providers claim that they are Tier 1 or Tier 2? Note: If you are looking for a much more detailed resource on this topic, please click here. Let’s start with the definition first. Tier 1 Service Provider A network, which does not purchase transit service from any other network, and therefore peers with every other Tier 1 network to maintain global reachability. They are the biggest guys geographically, but not always from the number of customers' points of view. Tier 2 Service Provider A network with transit connections, customers, and some peering, but that still buys transit service from Tier 1 Providers to reach some portion of the Internet. Tier 3 Service Provider A stub network, typically without any transit customers, and without any peering relationships. They generally purchase transit Internet connection from Tier 2 Service Providers, sometimes even from the Tier 1 Providers as well (I know some non-profit organizations which have a transit connection from Tier 1) Tier 1, Tier 2, and Tier 3 Service Providers The above picture shows the general idea behind Tier 1, Tier 2, and Tier 3 Service Providers' connections and relationships. Tier 2 Providers generally can be a peer with another Tier 2 and Tier 1 Service Providers only peer with other Tier 1. The logic behind is actually very simple. Tier 1 Service Providers don’t peer with Tier 2 because Tier 2 providers are potential customers of Tier 1 Service Providers. If they can be a customer and pay the money for the transit connection, why would give them peer connectivity (Peering is free, at least in theory) Unless the customer changes their path preference with communities, service providers almost always choose customer over peering links vs. transit links. They want to utilize the customer links because they pay for the transit service. Even though peering is free thus SPs don’t pay each other for the service, peering brings them some cost. (They need to have a connection to the IX and have a router and port in the IX). There are just 11 or 12 Tier 1 Service Providers in the world and some Tier 2 level Service Providers always claim that they are Tier 1. By doing it, they target to have a free peering relation with the other Tier 1 of course so they wouldn’t pay transit costs and have other Tier 2 SPs as their customers. The same thing is valid for the Tier 3 Service Providers as well. They might try to show them as Tier 2 to get free peering from the other Tier 2 Service Providers. But often the Service Providers put strict requirements for the peering so claiming may not help! Last but not least, some thoughts for my more advanced readers; if an ISP is Tier 1 for IPv4, is it also Tier for IPv6?

Published - Sun, 10 Apr 2022

Created by - Orhan Ergun

Do You Really Need Quality of Service?

Quality of service (QoS) is the overall performance of a telephony or computer network, particularly the performance seen by the users of the network. Above is the Quality of Service definition from Wikipedia. Performance metrics can be bandwidth, delay, jitter, packet loss, and so on. Two Quality Of Service approaches have been defined by the standard organizations. Namely Intserv (Integrated Services) and Diffserv (Differentiated Services). In this post, I will not explain each method or the special tools used in each method. Instead, which method makes sense in a particular design and which Quality of Service Tools can solve user needs without compromising the network design goals. Intserv demands each and every flow request bandwidth from the network and the network would reserve the required bandwidth for the user during a conversation. Think this is an on-demand circuit switching, each flow of each user would be remembered by the network. This clearly would create a resource problem (CPU, Memory, Bandwidth) on the network thus never widely adopted. Although with RSVP-TE ( RSVP Traffic Engineering ) particular LSP can ask for bandwidth from the network nodes, and in turn nodes reserve a bandwidth, the number of LSP between the Edge nodes of the network is orders of magnitude less than individual flows of the users. The second Quality of Service Approach is Diffserv (Differentiated Services) don’t require a reservation instead flows are aggregated and placed into the classes. Then each and every node can be controlled by the network operator to treat differently for the aggregated flows. Obviously, it can be scalable compared to the Intserv Quality of Service model. When you practice Quality of Service, you learn Classification, Marking, Queueing, Policing, and Shaping tools. And you are also told that in order to have the best Quality Of Service for the user, you need to deploy it from end to end. But where are those ends? The name of the nodes might differ based on business. On the Enterprise campus, your access switch is one end, and the branch router, data center virtual or physical access switches, and internet gateways might be on the other end. Or in the Service Provider business, the Provider Edge router is one end, other provider edge routers, data center virtual or physical access, internet gateways, service access devices such as DSLAM, CMTS devices might be another end. So an end-to-end principle will fail since the end-to-end domain might be too broad and too many devices to manage. But definitely, some tools make sense in some places in some networks. For example ” Policing ” in the Service Provider Networks. It can be used for billing purposes. The provider can drop the excess usage or charge for the premium service. Policing is deployed together with classification/marking But you don’t need to deploy QoS tools on the other nodes so those classifications and marking will locally make sense. This tool is also used for the Call Admission Control purpose. Imagine you have 200Mb links and each Telepresence flow requires 45Mb traffic. You can place 4 calls onto the link. If the 5th call is set up, all other 4 calls suffer as well since packets have to be dropped. ( 45 * 5 – 200 – buffer size) Another Quality of Service tool is Queueing; And in particular, it is used whenever there is an oversubscription. Oversubscription can be between the nodes ( On the links ) or within the nodes. If the congestion is within the node, queueing in the ingress direction is applied to protect some traffic (maybe real-time ) from the Head of Line Blocking in the switching fabric of the node. Or in the egress direction between the nodes to protect selective traffic. The problem is if there is enough traffic, buffers (queues) will get full, and eventually, all the traffic will be dropped no matter what queueing method ( LLQ, WFQ, CBWFW ) is used. So if you try to design end-to-end Quality of Service by enabling queueing to cover all possible oversubscription in the network you fail. When the congestion happens, some flows will just die a couple of milliseconds after another. The design tradeoff here is to add more bandwidth vs engineering all possible congestion points. I am not talking only about the initial QoS design phase but the complexity brought by the QoS in the design as well. Network Operator needs to manage, understand, and troubleshoot QoS during steady-state and in the case of failure as well. Bandwidth is getting cheaper and cheaper every day but the complexity of Quality of Service will stay there forever.

Published - Sun, 10 Apr 2022

Created by - Orhan Ergun

BGP LU - Labeled Unicast - RFC 3107

BGP LU - BGP Labeled Unicast was defined in RFC 3107. BGP LU is used so commonly in many different network architectures and frameworks. In this post, BGP LU is explained with its use cases. BGP LU - Labeled Unicast allows BGP to advertise an MPLS Label for the IPv4 and IPv6 Unicast prefixes. Those who know MPLS may know but let me remind you if an IP prefix is learned via IGP routing protocols such as OSPF and IS-IS, then LDP, RSVP, and Segment Routing can assign an MPLS Label. But if the prefix is learned via BGP, only BGP can assign an MPLS Label. Assigning a label by BGP for the IPv4 or IPv6 Unicast prefix is known as BGP Labeled Unicast. It is quite easy to understand what is BGP LU but at the beginning of the post, as I said, let's have a look at its use cases. BGP LU - RFC 3107 in Inter-AS MPLS VPN It is used in Inter-AS MPLS VPN Option C, between the ASBRs (Autonomous System Boundary Routers). In Inter-AS Option C, infrastructure prefixes of ASes are exchanged and for those prefixes, MPLS Label is assigned by BGP. Inter-AS MPLS VPN Option C is used when scalability is required, thus in general it is used when the scalability is the functional network design requirement (Must have requirement). BGP LU in Seamless MPLS Another scalability requirement is Seamless MPLS. The idea with the Seamless MPLS is to extend the MPLS control and data plane towards the Access domain, not just the Core or Aggregation parts of the network. With Seamless MPLS, in order to achieve this, loopback prefixes of the network nodes are carried in BGP. Because prefixes are carried in BGP, and MPLS is enabled even at the Access nodes, BGP has to assign an MPLS Label, that's why. we have it in Seamless MPLS as well. Figure - Seamless MPLS Control Plane - Source: www.juniper.net BGP LU in Carrier Supporting Carrier (CSC) Architecture Figure - Carrier Supporting Carrier - CSC Architecture Another architecture is Carrier Supporting Carrier. The idea with CSC, there is a Customer Carrier and Backbone Carrier. Customer Carrier advertises its own infrastructure prefixes to the backbone carrier and doesn't advertise its customer prefixes. So, customer prefixes of Customer carrier can be hidden and not advertised to the backbone carrier. Between Customer Carrier and Backbone Carrier, MPLS is enabled and as a routing protocol, BGP is used mainly. When BGP is used and MPLS enabled, yet again BGP LU comes into play!. So, whenever there is a scalability need, MPLS is used,  and BGP is used for IP prefix exchange, you will encounter BGP LU - Labeled Unicast. Cisco, Juniper, Nokia, Huawei, and many other big vendors support BGP LU as it is standard and RFC 8277 obsoleted RFC 3107 a couple of years ago.

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

MPLS Benefits 4 Very important things to understand!

MPLS Benefits and Advantages, Network Engineers should understand MPLS. In this post, we will look at what are the benefits of deploying MPLS in the Network, and the advantages of having MPLS-enabled infrastructure. MPLS is Multi-Protocol Label Switching as you might know already. Multi-Protocol because we can carry many different types of traffic over MPLS. MPLS is Multi-Protocol Technology Layer 2 and Layer 3 network traffic Ethernet, Frame Frame-Relay, ATM, TDM different types of traffic was carried over MPLS. Because it provides an abstraction layer for the protocols, it is possible to carry many different types of traffic that couldn't be possible with other technologies easily. MPLS is a Scalable Protocol If we talk about MPLS benefits, probably one of the most important ones would be MPLS Scalability. There is a popular belief that MPLS was invented because the packet processing resource requirement and lookup speed are faster with MPLS, compare to IP destination-based lookup. Because MPLS is just a switching operation on the Mid-Label Switch Routers - LSR, and MPLS Label is 20 bits long, compared to IP which is 32 bits long with IPv4 and 128 bits long with IPv6, MPLS was considered a better performance protocol, thus allows to grow, without adding extra device resources. MPLS has many Applications/Use Cases One of the main advantages of MPLS is it has many different use cases and services. Ina Minei went through these services in his MPLS Enabled Applications book. Figure - MPLS Enabled Applications MPLS Layer 2 based VPNs, LDP and BGP based, then MPLS Layer 2 VPN with EVPN, Classical EVPN for both Layer 2 and Layer 3 VPNs, 2457-based MPLS Layer 3 VPN, Carrier Supporting Carrier, Seamless/Unified MPLS, Segment Routing, Inter-AS MPLS VPNs, GMPLS, RSVP based MPLS for Traffic Engineering, RSVP-TE FRR, SRTE and Topology Independent Loop-Free Alternate, and the list goes on. All of the above architectures, services, and frameworks work because the underlying mechanism is MPLS. Some of them can work with other mechanisms as well but could it be secure as MPLS'?. Could they be scalable as MPLS?. Are they Multi-Protocol?. MPLS can provide Fast Reroute One of the MPLS benefits can be considered Fast Reroute. Fast Network Convergence is a very critical and desired behavior as of 2022 by almost any type of Network and Fast Reroute as one of the data plane protection techniques, can provide 50 ms. convergence time. This can be possible with MPLS technologies such as RSVP and Segment routing. MPLS can support Constrained-based Explicit Routing By using RSVP and Segment Routing with Path Computation Element (PCE), MPLS can support explicit, constrained-based routing. Meaning, that on the head-end router, the entire path can be defined with the user/network administrator constraint. You can request, 100Mb LSP between Point A and Point B, maybe based on time of the day, etc. Many different types of constrained can be defined and these are not again easily, in a scalable way possible with other technologies. Although there are many other MPLS benefits, to keep the short post, I will end the post here, but please check the other posts on the website as we have thousands of them and many also in MPLS topics.

Published - Fri, 08 Apr 2022

Created by - Orhan Ergun

IGP vs BGP Explained - 3 Most important things to know!

IGP vs BGP is one of the topics every Network Engineer want to learn in their career. In this post, without going into each IGP protocol detail, where and why IGP or BGP is used and should be used will discuss. As usual, we will look at it from a design aspect and understand the reasons for the protocol selection. IGP vs BGP comparison from a design perspective using a comparison chart Although I will not explain the above chart in this blog post in detail, I would like to share it for completeness. Also, please note that we compared BGP with each IGP protocol from a design point of view on the website in different blog posts already.IGP vs. BGP - BGP is the most scalable routing protocol! When igp vs BGP is compared, the first thing we should understand is that BGP is the most scalable routing protocol and it is used for the Global Internet. Global Internet, as of 2022, carries almost a million IPv4 Unicast prefixes. When we talk about IGP scaling, OSPF, IS-IS, or EIGRP, can carry couple of tens of thousand prefixes, and after that, we may start seeing meltdowns, even in well-designed IGP networks. BGP vs IGP - BGP Policy is more powerful! Another main reason BGP is preferred where it is preferred, such as Global Internet or MPLS VPNs, it is much more flexible when it comes to path manipulation. By using many different attributes, such as BGP Local Preference, BGP Communities, BGP Prepending, and many techniques, network traffic can be engineered in both Outbound and Inbound directions. With IGP protocols, usually, bandwidth is used to calculate the bandwidth, not many tools influence the path selection, and only the outbound direction traffic can be manipulated. BGP is used to carry customer prefixes in the Service Provider networks, and IGP protocols are used for the infrastructure device reachability. So, IGP is used for Transport, Underlay purposes but BGP is used for Service Layer, which means the Overlay mechanism. IGP vs BGP - BGP is Multiprotocol technology! Another big difference, between BGP vs. igp, BGP is multi-protocol technology. With MP-BGP support, BGP can carry 20 different Address families. 20 different purposes, IPv4 unicast, IPv4 multicast, IPv4 unicast, IPv6 multicast, EVPN, L2VPN, Security, Quality of Service, Multicast, and many other purposes, BGP can be used. IGP protocols are used usually just for IPv4 and IPv6 Unicast purposes, even for Multicast, a separate protocol, PIM is used with IGPs. Although many other things can be explained when we compare IGP vs BGP, my intent is to keep this post as short as possible, as I explained each of these comparisons, such as OSPF vs BGP, OSPF vs EIGRP, and different comparison variations in a different post on the website in detail.

Published - Fri, 08 Apr 2022

Created by - Orhan Ergun

OSPF LSA Types Explained 11 Types of LSA in OSPF!

OSPF LSA Types is the first topic you need to understand if you are trying to understand OSPF routing protocol. There are 11 different types of LSA in OSPF and we will look at each one of them, why do we have many different LSA in OSPF, we will discuss the topologies and the examples to make it more clear for everyone. What is LSA in OSPF? We should start asking the most fundamental question first about OSPF. What is LSA? LSA stands for Link State Advertisement and it carries, prefix information, interface cost, if advanced technologies such as Traffic Engineering are enabled, can carry link color information, used bandwidth, available bandwidth, and so on. When a router receives an LSA, it is stored in the Link State Database (LSDB) of OSPF. Once the LSDBs between the routers are synchronized, OSPF uses the SPF/Dijkstra algorithm to calculate the best path for each destination network. OSPF LSAs are information about a route that is transported inside OSPF Link State Update (LSU) packets. We can only have scalable, resilient, fast-converged OSPF design when we understand OSPF LSAs and Area types and their restrictions Figure -11 Different LSA Types is OSPF v2 OSPF LSA Type 1 - OSPF Router LSA OSPF Type 1 LSA/Router LSA packets are sent between routers within the same OSPF area and do not leave the area. An OSPF router uses Type 1 LSA to describe its own interfaces but also carries information about its neighbors to adjacent routers in the same area. OSPF Type 1 LSA is created by each and every router in a given OSPF area, as we will see in the other LSA types, some of them are only created by special types of routers. When the OSPF Prefix suppression type of feature is used, infrastructure prefixes are removed from Type 1 LSA, so OSPF scalability can be achieved. OSPF LSA Type 2 - OSPF Network LSA OSPF Type 2 LSA/Network LSA packets are generated by the OSPF Designated Router (DR) to describe all routers connected to its segment directly. Type 2 LSA is flooded between neighbors in the same OSPF area and doesn't cross the area boundary. Type 2 Network LSA is not desired if the OSPF connection is a point-to-point. Because there are only two points, no need for a DR/BDR election and also no need for extra Type 2 LSA. Type 2 LSA will be stored in OSPF LSDB and Routing table and their size will grow unnecessarily if the connection type is a point to point. We want DR/BDR election, thus Network LSA, only if the connection model is Multi-access. This means that in the segment, many OSPF routers are attached. Although it should be the subject of another post, let me just say here that, having DR/BDR election increases network convergence time. So, no Type 2/Network LSA unnecessarily!. OSPF LSA Type 3 - OSPF Summary LSA OSPF Type 3 LSA/Summary LSA packets are generated by the OSPF Area Border Routers (ABR) to summarize its directly connected OSPF area, and advertise inter-area router information to other areas to the ABR is connected. Type 3 LSA is only seen when there is a hierarchical OSPF network design, meaning an OSPF Multi-area network design. If there is only one OSPF area in the network, we can't have Type 3 LSA. OSPF LSA Type 4 - OSPF ASBR Summary LSA OSPF Type 4 LSA/ASBR Summary LSA is used to advertise the presence of an Autonomous System Border Router - ASBR in other areas. Inside the same area that we have an ASBR, ASBR reachability is achieved with OSPF Type 1 LSA. If there is Type 5 LSA, and if there is Hierarchical OSPF Network design, meaning OSPF Multi-area network design, then we can have OSPF Type 4 LSA. Otherwise, as it is said above, ASBR reachability is achieved via Type 1 LSA in a single area OSPF network design. OSPF LSA Type 5 - OSPF ASBR External LSA OSPF Type 5 LSA/ASBR External LSA in OSPF LSA Types is generated by the ASBR to advertise external redistributed prefixes into the OSPF domain. These external routes/prefixes are redistributed into the OSPF network by the ASBR and seen as either E1 or E2 entries in the routing tables of the routers. External LSA is domain-wide, meaning if we redistribute prefixes into OSPF, those redistributed prefixes are flooded everywhere, even if there are multiple areas in OSPF, every area receives them. Exceptions are Stub Area and its variations, such as Totally Stub Area, NSSA, and Totally NSSA Area. OSPF LSA Type 6 - OSPF Group Membership LSA OSPF Type 6 LSA was considered for the Multicast purpose, Multicast routing for OSPF but never implemented or deployed. Similar to the DVMRP protocol, it didn't last long and today for IP Multicast routing purpose, PIM - Protocol Independent Multicast is used. Although Type 6 LSA is not used, when we cover OSPF LSA Types, it was necessary to explain it too. OSPF LSA Type 7 - OSPF Not So Stubby Area (NSSA) External LSA OSPF Type 7 LSA/NSSA External LSA is seen in NSSA and Totally NSSA Areas when there is redistribution. Normally Stub Areas don't allow redistribution, but as a Not So Stubby Area (NSSA), redistribution is allowed. But, redistributed prefixes are not seen as Type 5 LSA, they are seen as Type 7 LSA. Type 7 LSA is translated to Type 5 LSA to be sent into the OSPF Area 0/Backbone Area. If there are two NSSA ABRs, they negotiate with each other and the NSSA ABR with the lower Router ID does the translation. OSPF LSA Type 8 - OSPF External Attributes LSA Normally BGP prefixes are redistributed into OSPF or any other routing protocol, and BGP attributes are lost. But, you may need to carry BGP attributes with your Autonomous System between the Routers. Let's say, for the given destination IP prefix, you have two exit points from your network, and for the outbound direction, you want to prefer one of those exit points as Primary. You can use this BGP Local Preference attribute. Two Routers exchange the prefixes with each other, and when they check the BGP Local Preference attribute, which every Router has the higher Local Preference, that router is used as an exit point by both of the routers. But BGP local preference e attributes cannot be carried in OSPF normally. Because of reachability, you need to redistribute from BGP to OSPF, and if you redistribute, attributes are lost. Type 8 LSA in OSPF LSA Types, was considered for this purpose. BGP Attributes would be carried even if we would redistribute. But yet another LSA that we don't use in computer networking. Instead of this LSA, IBGP - Internal BGP is used in the networks. Hope Type 8 LSA as one of the OSPF LSA Types is understood better now. OSPF LSA Type 9, 10, 11 - OSPF Link Scope Opaque LSA Opaque LSAs LSA Type 9, 10, and 11 are used to extend the capabilities of OSPF. With these LSA Types, OSPF carries many other protocol capabilities. For example, RSVP Traffic Engineering and Segment Routing Traffic Engineering requires topology information, used bandwidth, available bandwidth, reserved bandwidth, link coloring information, delay or other attributes, and so on. BIER - Bit Indexed Explicit Replication, the newest and most scalable Multicast architecture information is conveyed with Opaque LSAs as well. OSPF Graceful Restart/GR and many other use cases we have with Opaque LSAs. Think of it as a helper to the basic OSPF mechanism. In addition to carrying prefixes and cost, much other information can be carried with them. Type 9 LSA is link scope, Type 19 is Area scope and Type 11 is AS scope Opaque LSAs. What type of OSPF LSA is originated by ASBR routers to advertise external routes? Let's review what we have learned. The answer to this question is Type 5 External LSA. ASBR advertises external routes as Type 5 LSA and this LSA is flooded in every area in the OSPF domain if they are not Stub or NSSA. What information is contained within an OSPF type 4 LSA? Type 4 LSA is used for ASBR reachability as t was explained earlier in the post as well. But, it is seen only if there is a multi-area OSPF network. In a single area OSPF network design, ASBR reachability is achieved with ASBR's Type 1 LSA. OSPF LSA types are in general used for OSPF Scalability. Only with 1 LSA type, all the information could be carried. But when we have multiple areas, for hierarchy, we use different LSAs, as different LSAs have different duties. Understanding their restrictions and which one is allowed in which OSPF Area Types is very important to understand OSPF.

Published - Fri, 08 Apr 2022