Hi Rene,
I dont know if someone has mentioned the wrong information in your article regarding to BGP Summarization. You have mentioned that what R1 has in its routing table (can’t advertise what I don’t have!). The correct one is what R1 has in its BGP table (can’t advertise what I don’t have!). It means that R1 could have connected Interfaces in its Routing Table but not in its BGP Table so in this case R1 will not advertise the summary route because R1 doesn’t see these connected Interfaces in its BGP Table. When it comes to BGP Summarization, The Router will check if the subsets Networks are on its BGP Table not on its Routing Table.
You are correct that if a prefix is not in the BGP table it cannot be advertised to other BGP peers. However, a prerequisite of having a prefix in the BGP table is to have that route in the routing table.
Yes that is true, but it will only enter the BGP table if the route exists in the routing table. So the statement that Rene made is correct.
Rene compared BGP with IGPs and shows how they behave differently in the lesson called “How to advertise networks in BGP” In it he states the following:
When you use any of the IGPs (RIP, OSPF or EIGRP) then the network command is used to activate the IGP on all interfaces that fall within the range of the network command.
BGP doesn’t care about interfaces, it doesn’t even look at them. When we use the network command in BGP then BGP will only look at the routing table. When it finds the network that matches the network command, it will install it in the BGP table.
I was going through your GNS3Vault labs but could not find any lab specifically to try out troubleshooting BGP nighborship and route advertisement related issues.
Can you please design a troubleshooting lab for basic and advanced BGP features…or if there is already one that you have can you direct me there please … !!!
And Thanks alot for the amazing content as always !!!
RESPECT !!!
Beyond what’s available on the GNS3Vault, Rene doesn’t have any ready-made labs that can be used to troubleshoot BGP peering and route advertisements. However, in both of the following lessons, the topologies used are quite simple to recreate as they only involve two routers. I suggest you recreate these topologies and try out the various scenarios to get more accustomed to the possible errors that may occur.