A classic case of the issue of the effective order of bgp and ospf routing at a site

125x switches import routes

The routes learned by ebgp on site suppressed the routes imported by ospf, resulting in traffic not being implemented as expected: Preference 20 is configured on site, which will cause ebgp routing to be better than ospf routing. On site, if you configure preference first, bgp routing will take effect. If you configure route import first, ospf routing will take effect.

This problem does exist in laboratory reproduction:

1) Configure preference first and then import ospf:

2) Configure import ospf first and then configure preferences:

After analysis: 1) If you configure preferences first, the route learned by EBGP is 20 and the route learned by OSPF is 150. At this time, BGP routes are in effect in the routing table, and then import ospf is configured in BGP (Note: BGP can only import routes The effective route in the table), so it cannot be imported. At this time, BGP routing is effective; 2) When preference is not configured, the route learned by EBGP is 20 and the route learned by OSPF is 150. At this time, the effective route in the routing table is the ospf route type. In this case, configure import ospf in BGP first. Import the ospf route into the BGP routing table (pref-val 32768); then configure the preference. At this time, there are two in the BGP routing table, and the imported pref-val is large, so the BGP routing table is preferably OSPF