This topic is to discuss the following lesson:
Thank you Rene for making it easy to learn this kind of stuff
thanks your rene, you d best !
quick check : why you gave next-hope-self on 4. without that also I get the same result.
Without next-hop-self, R4 would learn the IP address of R1 as the next hop address. As long as you advertise the network in between R1/R2 into BGP, you will be fine. If you don’t, you have to use next hop self.
R2 do not send-community to R4, in this case what happens if R4 is connected to another AS ?
i think R4 will advertise the prefix because it does not any thing about the community, please correct me if wrong
You are exactly right! This is the output of R2 with respect to the BGP advertised route of 220.127.116.11
Origin IGP, metric 0, localpref 100, valid, external, best Community: no-export
If R2 isn’t configured to send communities to R4, this would be R4’s output of 18.104.22.168
Origin IGP, metric 0, localpref 100, valid, internal, best
Notice the community is missing. Because of this, R4 doesn’t know that it isn’t supposed to advertise this to another AS, so any other AS connected via R4 would also learn of 22.214.171.124/32
Many thanks for your support
In BGP community no export example.You said that it prevent route from being advertise to the ebgp peer and only advertise to IBGP neighbors. so why it is advertising to AS24 as it is also an ebgp peer for AS1. Router is in AS 1 and R2 ,R4 is in AS 24.Kindly explain.
R1 is the router that adds the no-export community, but the action does not apply to R1 itself. Only the router that receives the community has to process it, in this case R2.
Does this make sense?
ıf we connect another router R5(in AS 24 also) to R4, then can’t R4 advertise the 126.96.36.199 to R5? R5 is a iBGP neighbor so Why? Can R2 advertise to only it’s iBGP neighbors and can’t the other iBGP routers advertise to another iBGP neighbors?
If you have R5 in AS24 then yes, R2 will be able to advertise 188.8.131.52 to R5 as well. The No Export community only restricts routers from sharing particular routes with other eBGP neighbors. iBGP neighbors are not affected and they can freely share these routes between themselves.
Remember that this community is applied to particular routes, not to all routes in general. In this example, R1 sends the 184.108.40.206 route with the no export community set. This means that R2 will behave accordingly ONLY for that one particular route. All other routes can be shared freely according to the default behaviour of BGP.
I hope this has been helpful!