![]() Lastly, we will inform remote end about our loopback interface with BGP Update-source command Then, we will configure iBGP neighbor with neighbor’s interface IP address. Firstly, we will go to BGP process with Autonomous System number 100. So, we will use BGP neighbor update source command on this router under BGP process. On Router A, we will use loopback IP address to form iBGP neighborship. Test your Border Gateway Protocol (BGP) Knowledge with BGP Questions. Below, we will form iBGP neighborship in AS 100. You can also check bgp ebgp-multihop and bgp next hop self commands. Router(config-router)# neighbor update-source interface-type interface-number We use BGP Update-source command, like below under the BGP process. So, the neighbor router needs to inform BGP of the use of a Loopback interface. When we use loopback addresses for neighborship, this means that the routers will use this address as the source of the BGP packets. Because, by default, eBGP neighbors needs to be directly connected. For eBGP, it can be used but needs an additional multi-hop configuration. For this reason, we use loopback addresses to form BGP neighborship also.īy the way, update-source loopback command is normally used for iBGP neighbors. As you know, loopback interfaces are always up, they do not affect from any link failure and they never go down. To overcome this and for network stability, we use loopback interfaces. ![]() But using physical interfaces for such an important job can cause outage during a link failure or another neighborship forming in a production network. And TCP session establishment with Three-Way Handshake can be done over this neighborship. We can use physical interfaces and their IP addresses to form BGP neighborship. In this lesson, we will focus on this command and we will give an example for how to use loopback IP addresses to form BGP neighborships. At this time, we use BGP Update-source command. But sometimes we need to use loopback IP addresses to form BGP neighborship. To form a neighborship between two BGP routers, we use BGP neighbor command on Cisco routers. ![]() So in realistic cases, the next hop address of a received BGP route is an IP address that is not on a directly connected network which means that you first need to have a route to that next hop address, and that is why you need IGP.BGP works with neighborships. Surely, that's not how most AS are designed. Now you have to ask yourself: Can each of my routers directly reach every possible next hop IP address that can show up in a received BGP advertisement? If yes, you do not need an IGP - but that also means that your entire AS consists of a single broadcast domain and a single subnet - effectively a single LAN with all routers connected to it. What I am saying is that the next hop attribute can be set to various values. There are also other options of manually influencing the next hop attribute via route-maps. The AS border router that received this network via eBGP (intra-AS iBGP with next-hop-self).The advertising AS border router in the next autonomous system (classic eBGP). ![]() The router that injects this network into BGP (classic intra-AS iBGP).Remember that when BGP advertises a network, the IP address in the next hop value is a standalone attribute that can be set to the IP address of: This is not a matter of how many routers you have but rather whether they are all on the same directly connected network. So Question is, Does IBGP need IGP when we are using more than 2 routers? ![]()
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