In this post, we will compare BGP and OSPF. We will look at some of the important aspects when we compare BGP vs OSPF.
Although OSPF is used as an IGP and BGP is used mainly as an External routing protocol, we will compare from many different design aspects.
Also, BGP can be used as an Internal IGP protocol as well and we will take that into consideration as well.
We prepared the above comparison chart for BGP vs OSPF comparison. We will look at some of those important Comparison criteria from a design point of view.
BGP vs OSPF Scalability
One of the biggest reasons we choose BGP, not OSPF is Scalability. BGP is used as a Global Internet routing protocol and as of 2022, the Global routing table size for IPv4 unicast prefixes is around 900 000. So almost a million prefixes we carry over BGP on the Internet. So, proven scalability for BGP we can say. OSPF usually can carry only a couple of thousands of prefixes, this is one of the reasons, OSPF is used as an Internal dynamic routing protocol, not over the Internet.
BGP vs OSPF in Full Mesh, Ring and Hub and Spoke Topologies
The full mesh may require a lot of logical connections, meaning BGP neighborship or OSPF adjacencies. BGP Full Mesh is required because of the Split Horizon loop prevention requirement of BGP. But with the BGP Route Reflector, BGP can work well and can scale well in Full Mesh topologies. OSPF can scale with the mesh-group feature, DR election. capabilities as well. When it comes to large-scale Hub and Spoke topologies, OSPF requires a lot of tuning or it scales very poorly. Because Hub to Spoke connections either will be in the Backbone area, in this case, the backbone can get very large, or we may need to make Hub routers as ABR. It may not be possible always. Ring topologies are usually a nightmare for many aspects of every routing protocol. Converge slowly, hard for the capacity planning as well.
BGP vs OSPF Fast Reroute
OSPF can support Fast Reroute with LFA, Remote LFA, TI-LFA, and RSVP-TE FRR. BGP also with BGP PIC, Prefix Independent Convergence supports BGP Fast Reroute, so both protocols can give us data plane protection opportunity.
BGP vs OSPF Standard
When we compare OSPF vs BGP from their standardization point of view, we need to know that both are IETF standard protocols. On IETF for both of these protocols, maybe over 100 RFCs, we have!.
BGP vs OSPF Complexity
BGP supports many different address families and their purposes, use cases, and configuration, making in real-life BGP much harder to configure, troubleshoot and engineer compare to OSPF networks.
BGP vs OSPF Policy Support
Another most important reason we choose BGP is when we need to deploy policy, its excellent policy support. This means, that if we want to engineer the traffic inbound or outbound, BGP gives us many tools to do it. OSPF has only bandwidth, which is used as a metric, and its used for the Outbound traffic engineering/path manipulation purpose only.
BGP vs OSPF Resource Requirement
BGP if there are so many prefixes may require a lot of CPU and Memory. OSPF also for running SPF algorithm might require a good amount of device resources but in today's hardware, it can be easily handled by the routers.
BGP vs OSPF Extendibility
BGP is a TLV based protocol, but OSPF fixed header, so when it comes to extendibility, BGP is also a clear winner. Also, let's not forget today, BGP supports more than 20 different Address families with its MP-BGP, Multi-Protocol BGP support.
BGP vs. OSPF IPv6 Support
Both BGP and OSPF support IPv6 of course. OSPF with the OSPFv3, which is a completely new routing protocol and has many differences from OSPFv2, but BGP supports IPv6 as just a new BGP AFI, SAFI.
BGP vs OSPF Convergence
From the network convergence point of view, BGP is always known as a slow converged protocol. But saying BGP is slow, is wrong. If we understand Network Convergence better, we have two types of convergence. Control plane convergence and Dataplane convergence. It is a huge topic and we have a separate very detailed Network Convergence Course on the website. But overall, Data plane convergence is Fast Reroute and with the BGP PIC feature, BGP can support Fast Reroute, thus, it can converge so fast too.
Thus, maybe saying BGP Control plane convergence might be slow, due to a number of prefixes, device hardware, BGP TCP input queue, whether there is BGP RR or Full mesh, and many factors. Although there can be many other criteria to compare OSPF BGP, for this blog post, I think it is enough. If you want to more about it, you can take our BGP course or you can check many of our free blog posts on this topic.