The EIGRP and OSPF are the interior gateway routing protocols which help in selecting the routes for transferring or sharing the data through interacting with the routers. The former protocol, EIGRP employs a distance vector routing protocol while the latter one, OSPF uses a link-state routing protocol.
However, the capability of EIGRP and OSPF to learn the dynamic routes for the network is functionally equivalent, but there are several differences between them. Such as the EIGRP is Cisco proprietary IGP, which means it is only popular in Cisco networks only. On the other hand, OSPF is the open standards IGP for the enterprise network.
Content: EIGRP Vs OSPF
Comparison Chart
| Basis for comparison | EIGRP | OSPF |
|---|---|---|
| Stands for | Enhanced Interior Gateway Protocol | Open Shortest Path First |
| Standards-based on | Cisco Proprietary | IETF Open Standard |
| Protocol type | Hybrid | Link state |
| Routing metrics | Combination of bandwidth, reliability, load and delay. | Interface bandwidth |
| Administrative distance | 90 (Internal) 170 (External) | 110 |
| CPU requirements | Lower CPU and memory needs | Require high CPU and memory |
| Algorithm | DUAL distance vector | Dijkstra link state |
| Hierarchical design | No | Yes |
| Support of IPX and AppleTalk | Yes | No |
| Updates | Updates and queries as needed to a multicast address | Flooding as needed and periodically to a multicast address |
| Ease of implementation | Easy but no provision of auto-summary | Complicated |
| Loop prevention | Split horizon and DUAL | Full knowledge of topology |
| Filtering and summarization | Possible anywhere in the network | Only on ASBRs or ABRs |
Definition of EIGRP
EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco-based distance vector protocol which works on DUAL (Diffusing Update Algorithm). It is used for sharing the information from one to the neighbouring routers which exist within the same area. Although, it is a complex protocol but we can configure and run it easily in small and large networks. It was devised to overcome the shortcomings of the classical distance vector routing protocols like IGRP and RIP which were hard to scale according to the needs of the network.
EIGRP is considered as a hybrid because it merges the features of the distance vector routing and link-state routing protocol. Similar to the distance vector routing protocol, EIGRP receives its updates from its neighbours. In the same way, EIGRP stores a topology table of the advertised routes and utilizes the Diffusing Update Algorithm (DUAL) in order to select a loop-free path as the link-state protocol.
Before understanding the convergence in the EIGRP we must understand what convergence is. The convergence time in a network is the time that is consumed for all the routers in the network to accept the network change. If the convergence time is less the router can swiftly adapt the network topology change. The EIGRP does not send full periodic routing updates, that is the reason it has fast convergence time. While, EIGRP is not aware of entire network connections, so it relies on its neighbour’s advertisement.
Definition of OSPF
OSPF (Open Shortest Path first) is also a routing protocol like EIGRP but it is an open IETF standard which can be used and deployed in a variety of networks. The main idea behind the development of the OSPF protocol is to develop a link-state protocol which could provide more efficiency and scalability than RIP. OSPF uses protocol number 89 when it runs over the IP, similar to TCP which runs on the top of IP utilizes protocol number 6. It has a reliable mechanism for transportation rather than having a transport protocol like TCP.
The OSPF is a classless routing protocol that also assists variable-length subnet masking (VLSM) and discontiguous networks. To send Hello and updates it uses multicast addresses – 224.0.0.5 and 224.0.0.6. There is also the provision of authentication its two types are a plain test and message-digest algorithm 5.
As it is mentioned above that the OSPF uses the Dijkstra algorithm in order to calculate the routes by generating the shortest path tree (SPT). In link-state advertisements, each router shows itself and its links to the neighbours in a clear and understandable form, so that the OSPF can layout the network topology on the basis of the information from shortest-path tree.
The type of information that is interchanged between the routers is cost, type of link and network information with other routers and this process is known as LSA (link-state advertisement) exchange.
Key Differences Between EIGRP and OSPF
- EIGRP is an advanced distance vector routing protocol which uses incremental and triggered updates. Here, the triggered updates signify that the router will not send updates until and unless something has changed. Further, the incremental updates mean that the router will not send all the information about the network rather just the information that has changed will be shared. On the other hand, OSPF is a link-state routing protocol which resembles a map where the complete information about all the routes within that area is maintained. Whenever there is any change in the area, all routers in that particular area are needed to recalculate their database and routes. This makes the OSPF more CPU intensive as compared to EIGRP and since it has to store the information about the routes, its database also requires more RAM.
- For the backward compatibility with the older routers, the EIGRP is the better option relative to the OSPF.
- When it comes to convergence time, the EIGRP has less convergence time as it uses DUAL algorithm where the best path and the alternative best path is selected. If the best path goes wrong it can fall directly to the alternate best path. In contrast, OSPF follows a different approach due to which it has a greater convergence time.
- The OSPF requires meticulous planning of the area whereas there is no such requirement in the EIGRP; in fact, it is very good for the multivendor environment.
- Scalability of the OSPF is higher than EIGRP because EIGRP is complicated and vendor-specific and incapable of migrating from one vendor to the other. Conversely, OSPF is an open standard and simple protocol through which the network can be scaled easily.
- EIGRP is the only protocol that supports the unequal path load balancing while OSPF does not have this feature.
- The service provider and data centre support is better in OSPF as it is widely used in the traditional systems and it also facilitates the sharing of the routing information.
Metric and path selection
EIGRP – It has various factors to determine the overall metric for a particular destination such as bandwidth, delay, load, reliability, hop count and MTU. However, for the default metric calculation, it only uses bandwidth and delay.
In order to select the path, the EIGRP employs the concept of a successor, feasible successor, reported distance and feasible distance. In the first step, the successor is considered to be the best next-hop router for a given destination. The downstream next-hop router is responsible for reporting the distance to a given destination as the reported distance. The receiving EIGRP router accepts the received reported distance and derives the feasible distance by adding its respective interface metric. All of the accessible paths to the destination are examined and compared against each other among which the best path is selected. Here, the feasible successor signifies the alternate best next-hop router to a given destination.
OSPF – Unlike EIGRP, the OSFP considers mainly simple path cost to determine the metric for a given prefix destination. In order to calculate the path cost, the reference bandwidth is divided by the interface bandwidth. Process of path selection starts by choosing the lowest cost path as the best path for a destination. Although the OSPF areas also affect the path selection process. So, the OSPF follow the below-given pattern to select the path:
- Intra-area routes: These are the routes which were learned inside the area.
- Inter-area routes: It includes the routes that were learned from outside the area.
- External routes: Routes that do not exist in the OSPF autonomous system and learned outside of it.
Conclusion
When we compare the protocols EIGRP and OSPF, the EIGRP is quite complicated while OSPF is simpler because it uses just cost as the metric. The main difference between these protocols is that EIGRP exchanges the complete routing information just one time when the neighbouring routes are established after that it only tracks the changes. On the contrary, OSPF keeps track of the whole topology database of all the connection in the database consistently.
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