iBGP into OSPF

[louis0001]

Hi,

we have two core sites  (OSPF) & 50 satellite sites (MPLS BGP)

I want to redistribute the BGP into OSPF so if the BGP router at site A (default data site) goes down, traffic from the MPLS will reach site A via site B (see attached pdf)

Now if I go to enter "bgp redistribute-internal" it has in brackets (dangerous) next to it which is quite alarming to say the least. 

Is this just because there is the potential for BGP to dynamically inject networks eg by misconfiguration etc into the OSPF routes?

The MPLS network is a closed network although it is run by our ISP and our external access is via routers at site A & B.

So, is there any danger of redistributing BGP & OSPF to each other in this instance?

[SHOPE1]

We do this a lot with OSPF or EIGRP on a campus network or where multiple WANs connect to a common site.

If you are treating this as 1 site you may want site of origin across the BGP links to the campus.

You need to control which routes prefer which links - either by biasing the adverts or by advertising more specific routes on the preferred access.

You do need to control routes going from OSPF to BGP and back, via route-maps.

What we do is in the BGP -> OSPF
- redist all the BGP routes into OSPF
- tag the routes injected with a value

For OSPF -> BGP
- block routes carrying the tag
- set a preference if needed
- aggregate routes if needed

If you use default routes you need to think about whether you want to propagate a default from 1 domain to the other.