BGP into OSPF

From: ccie8966 (ccie8966@wanadoo.fr)
Date: Sun Jan 04 2004 - 19:49:29 GMT-3

Hi,

in this lab topology (not a "real-life" one), we connected
two routers back-to-back. An OSPF adjacency is full between R1
and R2. And we configured R1 to redistribute BGP into OSPF
(but it could be EIGRP, no difference).
R1 doesn't have any BGP peer, but just a network statement for
1.0.0.0/8 and a static to null0. 

---

R1 config :
router ospf 1
 redistribute bgp 1
 network 192.168.1.0 0.0.0.255 area 0
!
router bgp 1
 no synchronization
 bgp redistribute-internal
 network 1.0.0.0
 no auto-summary
!
ip route 1.0.0.0 255.0.0.0 Null0

---

R2 config :
router ospf 1
 log-adjacency-changes
 network 192.168.1.0 0.0.0.255 area 0

---

I used to think that redistribution was done by "scanning"
the routing table and by picking the entries matching the criteria
(for instance, the entries learnt via BGP).
Here, 1/8 appears in the bgp table but isn't installed in the routing
table (appearing as a "connected" static) :

R1#sh ip bgp
BGP table version is 2, local router ID is 192.168.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 1.0.0.0          0.0.0.0                  0         32768 i

R1#sh ip ro 1.0.0.0
Routing entry for 1.0.0.0/8
  Known via "static", distance 1, metric 0 (connected)
  Redistributing via ospf 1
  Advertised by ospf 1
  Routing Descriptor Blocks:
  * directly connected, via Null0
      Route metric is 0, traffic share count is 1

But the route 1/8 is redistributed into OSPF :

R2#sh ip ro 1.0.0.0
Routing entry for 1.0.0.0/8
  Known via "ospf 1", distance 110, metric 1, type extern 2, forward metric 64
  Last update from 192.168.1.1 on Serial1/0, 00:13:38 ago
  Routing Descriptor Blocks:
  * 192.168.1.1, from 192.168.1.1, 00:13:38 ago, via Serial1/0
      Route metric is 1, traffic share count is 1

When I replace the static to null0 by a static to a next-hop addy, the route is no longer
redistributed.

I would like to understand what is the logic behind that.
When we redistribute from BGP to an IGP protocol, is it the routes from the routing
table or from the BGP table that must be taken into consideration ?

Cheers,

Nicolas.

This archive was generated by hypermail 2.1.4 : Mon Feb 02 2004 - 09:07:36 GMT-3