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What are the difference between the EBGP, IBGP and IGP ?

Where do the EBGP, IBGP and IGP MA5600T can be used, and what are the function? What are the difference and connection between them? Now, here are the detail for you.

As we know, in the autonomous system for internal use IGP routing protocol; and the use ofBGP routing protocol between autonomous systems (strictly speaking, BGP is not a routing protocol). BGP causes in different autonomous systems (AS) for routing and forwarding,which is proposed by EBGP and IBGP two. EBGP used in between different autonomous systems, but IBGP, the book says it is used in the autonomous system, but in theautonomous system we use is IGP. This and "BGP is the contradiction between" different autonomous systems, so the significance of the existence of IBGP, such as some kind ofsituation, need to use IBGP, it plays a role in the network? The difference between EBGP and IBGP? EBGP plays any role in the network?

Why for the IBGP, the following reasons:

1, the ability of IGP to limit, IGP routing entries is limited, and the current Internet core router's routing table has more than 100000. If there is no IBGP, so the routing can only take theweight distribution directly into IGP, this drawback is obvious: first, the IGP protocol of the authors and not going to allow IGP to handle such a large number of routing, IGP itself can't handle this kind of routing number; second, if not to let IGP processing, then according to theprinciple of IGP, if change any route 100000 route, then run the IGP router will have to reroute calculation, more serious is, if one of the routing routing jitter, such as repeatedUP/DOWN port, which can lead to all the time all the router IGP have to put 100000 routes to calculate again, this calculation is not affordable for most routers. In addition to running the RIP V1 router, regularly updated 100000 route, it is unable to accept things, remove thebandwidth occupancy rate not to talk about, I think, is only a small number of high-end GSRand TSR to have such properties. Obviously, we can't let the network all routers are GSRand TSR, if that is true, then Cisco, juniper and Huawei and other manufacturers will be lucky. For example: AS100----AS200---AS300, assuming AS100/200/300 each have 100 routers, and AS100 in the 1W route to transfer to AS300, and AS200 routers do not need to learn AS100 routing. If there is no IBGP, so the 1W route must be distributed to AS200 IGP,in this way, the equivalent of AS200 in all the 100 routers have increased the 1W route. If the use of IBGP, then AS200 only run IBGP routers will learn the 1W route, the other running IGProuters do not learn the 1W route. And because the BGP routing control ability is stronger than the IGP routing control ability, thus running the IBGP router is better than running the IGProuter to the 1W routing process routing strategy, so as to ensure that the number of routeacross the AS router to learn can be controlled in an acceptable range.

2, the routing loop problem. BGP is by routing property to prevent routing loops, such as the AS_PATH attribute, if no IBGP protocol, then when all BGP routing redistributing into IGP,routing is inevitably lost, it destroys the BGP mechanism to prevent routing loops, produced arouting loop problems.

So how, since IBGP can transmit routing prefix all, why still need to IGP?

1, the IBGP is connected to the TCP, it means IBGP neighbor are used the logic connection,the physical link two IBGP connection may not be the actual existence of the. So it is necessary to have the IGP to provide routing, BGP routing to a recursive lookup.

2, the BGP protocol itself does not actually found routing, BGP routing discovery work all over to the IGP protocol, it focuses on the routing control. Therefore, if there is no IGP, then BGPis of no use.


The difference between EBGP and IBGP:

1, a routing loop prevention measures are not the same, IBGP mandated iBGP speaker does not allow the transfer of the prefix from a iBGP neighbor to neighbor to other iBGP, so IBGPlogic connection. EBGP has no such requirement, EBGP on routing loop is suppressed bythe AS_PATH property is achieved.

2, using the BGP property is different, for example IBGP can transfer LOCAL_PREF (local preference attribute), but not EBGP.

3, IBGP has the synchronization requirement, while EBGP has no synchronizationrequirements

4, IBGP does not need to have a physical connection between IBGP neighbors, need onlylogical connection, and EBGP generally requires the existence of a physical connectionbetween EBGP neighbors.

What is the role of EBGP in the network? This topic is too big, EBGP I think is to providerouting transmission and routing X1CA control between different AS, understand the use of the BGP attribute, also understand the role of EBGP.
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