Redistribution between BGP to OSPF

[kousikdutta]

Hi, I am new in redistrution. I have configured the routers. I can see OSPF routes into BGP. However not able to see the BGP router in OSPF as external route. Kindly suggest me how should I configure to get it.

Topology: Attached.

R1:

R1#sh run | s r ospf
router ospf 1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 12.1.1.0 0.0.0.255 area 0
network 14.1.1.0 0.0.0.255 area 0
R1#
R1#
R1#sh ip int br | ex down|unass
Interface IP-Address OK? Method Status Protocol
Ethernet1/0 12.1.1.1 YES NVRAM up up
Ethernet1/1 14.1.1.1 YES NVRAM up up
Loopback0 1.1.1.1 YES NVRAM up up
R1#

R2:

*Nov 24 21:11:40.607: %SYS-5-CONFIG_I: Configured from console by console
R2#sh run | s r bgp
router bgp 235
no synchronization
bgp log-neighbor-changes
network 2.2.2.2 mask 255.255.255.255
redistribute ospf 1
neighbor 23.1.1.3 remote-as 235
neighbor 23.1.1.3 next-hop-self
no auto-summary
R2#sh run | s r ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
redistribute bgp 235 subnets
R2#
R2#sh ip int br | ex down|unass
Interface IP-Address OK? Method Status Protocol
Ethernet1/0 12.1.1.2 YES NVRAM up up
Ethernet1/1 23.1.1.2 YES NVRAM up up
Loopback0 2.2.2.2 YES NVRAM up up

R5:

R5#sh run | s r bgp
router bgp 235
no synchronization
bgp log-neighbor-changes
network 5.5.5.5 mask 255.255.255.255
redistribute ospf 1 match internal external 1 external 2
neighbor 53.1.1.3 remote-as 235
neighbor 53.1.1.3 next-hop-self
no auto-summary
R5#sh run | s r ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
redistribute bgp 235 subnets
R5#sh ip int br | ex down|unass
Interface IP-Address OK? Method Status Protocol
Ethernet1/0 45.1.1.5 YES NVRAM up up
Ethernet1/1 53.1.1.5 YES NVRAM up up
Loopback0 5.5.5.5 YES NVRAM up up
R5#

R3:

R3#
R3#sh run | s r bgp
router bgp 235
no synchronization
bgp log-neighbor-changes
network 3.3.3.3 mask 255.255.255.255
neighbor 23.1.1.2 remote-as 235
neighbor 53.1.1.5 remote-as 235
no auto-summary
R3#
R3#
R3#
R3#sh ip bgp su
BGP router identifier 3.3.3.3, local AS number 235
BGP table version is 28, main routing table version 28
9 network entries using 1080 bytes of memory
15 path entries using 780 bytes of memory
8/5 BGP path/bestpath attribute entries using 992 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
Bitfield cache entries: current 1 (at peak 2) using 32 bytes of memory
BGP using 2884 total bytes of memory
BGP activity 16/7 prefixes, 23/8 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
23.1.1.2 4 235 53 42 28 0 0 00:17:44 6
53.1.1.5 4 235 46 38 28 0 0 00:13:54 8

R4:

e
R4#sh ip int br
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES NVRAM administratively down down
Ethernet1/0 14.1.1.4 YES NVRAM up up
Ethernet1/1 45.1.1.4 YES NVRAM up up
Ethernet1/2 unassigned YES NVRAM administratively down down
Ethernet1/3 unassigned YES NVRAM administratively down down
GigabitEthernet2/0 unassigned YES NVRAM administratively down down
Loopback0 4.4.4.4 YES NVRAM up up
R4#sh ip int br | ex down
Interface IP-Address OK? Method Status Protocol
Ethernet1/0 14.1.1.4 YES NVRAM up up
Ethernet1/1 45.1.1.4 YES NVRAM up up
Loopback0 4.4.4.4 YES NVRAM up up
R4#sh run | s r os
router ospf 1
log-adjacency-changes
network 4.4.4.4 0.0.0.0 area 0
network 14.1.1.0 0.0.0.255 area 0
network 45.1.1.0 0.0.0.255 area 0
R4#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/11] via 14.1.1.1, 00:39:07, Ethernet1/0
2.0.0.0/32 is subnetted, 1 subnets
O E2 2.2.2.2 [110/20] via 14.1.1.1, 00:03:55, Ethernet1/0
4.0.0.0/32 is subnetted, 1 subnets
C 4.4.4.4 is directly connected, Loopback0
5.0.0.0/32 is subnetted, 1 subnets
O E2 5.5.5.5 [110/20] via 45.1.1.5, 00:13:30, Ethernet1/1
53.0.0.0/24 is subnetted, 1 subnets
O E2 53.1.1.0 [110/20] via 45.1.1.5, 00:13:30, Ethernet1/1
23.0.0.0/24 is subnetted, 1 subnets
O E2 23.1.1.0 [110/20] via 14.1.1.1, 00:03:55, Ethernet1/0
12.0.0.0/24 is subnetted, 1 subnets
O 12.1.1.0 [110/20] via 14.1.1.1, 00:21:17, Ethernet1/0
14.0.0.0/24 is subnetted, 1 subnets
C 14.1.1.0 is directly connected, Ethernet1/0
45.0.0.0/24 is subnetted, 1 subnets
C 45.1.1.0 is directly connected, Ethernet1/1

The redistribution happened on R2 and R5. Kindly suggest how I can see the bgp routes in pspf

R1----------R2

|                                R3

R4  --------R5

[Richard Burts]

I find the topology diagram not clear. It seems clear that R1 connects to R2 and that R4 connects to R5. But what does R3 connect to? Is the connection R1 to R3 to R4 or is it R2 to R3 to R5? Does this suggest that R2 and R5 are on the outside edge of the organization network?

In looking at what is posted I believe that I see at least one issue. In the configuration of ospf I do not see any network statements:

R2#sh run | s r ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
redistribute bgp 235 subnets

If the bgp routes are being redistributed where would you expect to see the redistributed routes? Who would R2 advertise the redistributed routes to? on R2 the routes would be BGP routes. They would only be OSPF external on some router that R2 advertises to.

[MHM Cisco World]

R2 R3 R5
you need command no synch under each ibgp router.
try and see result. 

[Georg Pauwen · Accepted solution]

Hello,

to be honest, I cannot figure out your topology either. You redistribute BGP into OSPF on two routers ?

R2#sh run | s r ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
redistribute bgp 235 subnets

R5#sh run | s r ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
redistribute bgp 235 subnets

Either way, in the BGP process on the redistributing routers, you need to configure 'redistribute bgp-internal:

R2

router bgp 235

redistribute bgp-internal

R5

router bgp 235

redistribute bgp-internal

[Giuseppe Larosa · Accepted solution]

Hello @kousikdutta ,

Georg is right you have iBGP sessions = same BGP AS number so by default iBGP routes are not redistributed into an IGP like OSPF unless in router bgp configuration you add the command

router bgp 235

bgp redistribute-internal

To be noted this is not common practice in real world where the IGP is used to be able to setup iBGP sessions and all service related advertisements are carried in BGP,

Hope to help

Giuseppe

[kousikdutta]

Hi Giuseppe,

Thanks for yor comment. That is the reason I have tried to use Prefix-list , then configured the route-map and this route-map added in the interface to get the BGP route in OSPF. 

Could you please suggest wheather is there any other option that I can use to get this BGP route in OSPF.

Thanks,

[Giuseppe Larosa]

Hello @kousikdutta ,

the command in router bgp to allow redistribution of iBGP routes into IGP like OSPF can be seen as a protection mechanism:

a) from a scalability point of view BGP can support much more routes then any IGP hundreds of thousands of routes instead of tens of thousands so it is a protection for OSPF

b) if all routers are running both BGP and OSPF this redistribution is not necessary and OSPF is used to provide loopback advertisements and inter router links (infrastructure) and all everything else (services ) is carried in BGP

>> Could you please suggest wheather is there any other option that I can use to get this BGP route in OSPF.

As far as I know as I have explained above there is no other way to get an iBGP route redistributed into OSPF.

Hope to help

Giuseppe