What is the difference between EBGP/IBGP/IGP?

We know that the IGP routing protocol is used inside the autonomous system, while the BGP routing protocol is used between different Autonomous Systems (strictly speaking, BGP is not a routing protocol ). BGP is generated to forward routes between different Autonomous Systems (AS), and EBGP and IBGP are proposed. EBGP is used between different autonomous systems, but IBGP is used in autonomous systems, but IGP is used in autonomous systems. This is in conflict with "BGP is applied to different Autonomous Systems". What is the significance of IBGP? For example, in some cases, IBGP needs to be used. What is the role of IBGP in the network? What is the difference between EBGP and IBGP? What role does EBGP play in the network?

Why IBGP is required? The reasons are as follows:

1. the IGP capability is limited. The number of Route entries processed by IGP is limited. At present, the number of Route tables of core routers on the internet exceeds 0.1 million. If there is no IBGP, these routes can only be directly imported to IGP by means of redistribution. the disadvantages of doing so are obvious: first, the author of the IGP protocol does not intend to allow IGP to process such a large number of routes, and IGP itself cannot process such a large number of routes. Second, if IGP is required to process the routes, according to the IGP processing principle, if any route in the 0.1 million route changes, the router running IGP has to re-calculate the route. More seriously, if a route in the route is jittery, for example, the port is UP or DOWN repeatedly, this will cause all the IGP routers to have to re-calculate the 0.1 million route entries every moment, this computing workload cannot be borne by the vast majority of routers. In addition, for Routers running RIP V1, the regular update of 0.1 million routes is simply unacceptable. Aside from bandwidth usage, I think, only a small number of high-end GSR and TSR can have such performance. Obviously, we cannot make all the routers in the network be GSR and TSR. If so, Cisco, juniper, Huawei, and other manufacturers will have to laugh. For example: AS100----AS200---AS300, assuming AS100/200/300 each has 100 routers, and AS100 has 1 W route to be transferred to AS300, and AS200 Router does not need to learn AS100 route. If there is no IBGP, all the 100 routes must be re-distributed to the IGP of AS200. In this way, routes are added to all routers of AS200. If IBGP is used, only the routers running IBGP in AS200 will learn the route entries, and the other routers running IGP will not learn the route entries. In addition, because the BGP routing control capability is much stronger than the IGP routing control capability, the IBGP-running router can perform some Routing Policy Processing on these routes better than the IGP-running router, this ensures that the number of routes learned by the routers within the AS can be controlled within the acceptable range.

2. routing loop problems. BGP relies on Route attributes to prevent routing loops. For example, if the AS_PATH attribute does not have the IBGP protocol, the routing attributes will inevitably be lost when all BGP routes are redistributed to IGP, this destroys the BGP routing loop prevention mechanism and creates a hidden risk of routing loops.

Now that IBGP can transmit all the route prefixes, why does it need IGP?

1. IBGP is a TCP connection, which means that the IBGP neighbor adopts a logical connection. The two IBGP connections do not necessarily have physical links. Therefore, IGP is required to provide routes for recursive search of BGP routes.

2. The BGP protocol itself does not actually discover routes. BGP transfers all routing discovery work to the IGP protocol, which focuses on route control. Therefore, without IGP, BGP is useless.

Difference between EBGP and IBGP:

1. The preventive measures for routing loops are different. IBGP enforces that ibgp speaker cannot pass the prefix learned from an ibgp neighbor to other ibgp neighbors. Therefore, IBGP requires full logical connection. EBGP does not have such requirements. EBGP avoids routing loops through the AS_PATH attribute.

2. The BGP attributes used are different. For example, IBGP can pass LOCAL_PREF (local priority attribute), but EBGP cannot.

3. IBGP has synchronization requirements, while EBGP does not.

4. IBGP does not require a physical connection between IBGP peers. It only requires a logical connection, while EBGP generally requires a physical connection between EBGP peers.

What role does EBGP play in the network? This topic is too big. In my opinion, EBGP provides route transmission and route control between different AS, understands the usage of BGP attributes, and also understands the role of EBGP.

Original blog link: http://blog.sina.com.cn/s/blog_6ceed3280101ehja.html