[c-nsp] BGP question

[James Hampton]

I am seeing some unexpected behavior. I have 2 boarder routers each
are IBGP together and EBGP with there perspective providers. On br2 I
have a prefix list with all our internal prefixes going out and
another filtering bogons in, so far so good. But I currently only have
1 network statement with one prefix advertised so I can test the link
on br2. All was good when I checked the providers route server I only
saw the 1 network I was advertising. Than when I brought up IBGP
between the two boarder routers and suddenly all our internal prefixes
were learned by the provider on br2 even though I was only explicitly
advertising 1 network via the network statement. Does a router
automatically advertise prefixes learned from an IBGP peer to a EBGP
peer?