I understand that in order for a router to advertise networks to another router over eBGP you need a network command for the subnet and mask. In addition, it has to be an exact match in the routing table as well. However, I set up a lab that has a router advertising a subnet to an eBGP peer without a network statement but I think I know why but would like someone's else's thoughts on this as well. The edge router "a" peers with router "b" over eBGP. Edge router "a" also peers with router "c" over iBGP. Router "c" is advertising 10.250.3.0/24 to edge router "a" over iBGP. So I see 10.250.3.0/24 on edge router "a" but I do not have a network statement to advertise it to router "b". Is the reason that router "b" is receiving that route is because anytime a router learns about a route from an iBGP neighbor it automatically advertises it to its' peers? I ask because when I create a loopback interface directly on router "a" and no network command to advertise it, router "b" does not see that route as expected.
Thank you
