Elements
In this example we
will examine a hidden command: bgp redistribute-internal
R1 is running OSPF
with R2, iBGP with R3 (EIGRP is for loopbacks connectivity) and eBGP with R4
As known, when we
redistribute BGP into a routing protocol, only eBGP routes are redistributed,
let us find and see
Configuration
R1
interface
Loopback0
ip address 1.1.1.1 255.255.255.255
interface
FastEthernet0/0
ip address 192.168.12.1 255.255.255.0
speed 100
full-duplex
interface
FastEthernet0/1
ip address 192.168.13.1 255.255.255.0
speed 100
full-duplex
interface
Serial0/0
ip address 192.168.14.1 255.255.255.0
encapsulation ppp
router
ospf 1
router-id 1.1.1.1
log-adjacency-changes
redistribute bgp 1 subnets
network 192.168.12.1 0.0.0.0 area 0
router
eigrp 1
network 1.1.1.1 0.0.0.0
network 192.168.13.1 0.0.0.0
no auto-summary
router
bgp 1
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 update-source Loopback0
neighbor 192.168.14.4 remote-as 4
no auto-summary
R2
interface
Loopback0
ip address 2.2.2.2 255.255.255.255
interface
FastEthernet0/0
ip address 192.168.12.2 255.255.255.0
speed 100
full-duplex
router
ospf 1
router-id 2.2.2.2
log-adjacency-changes
network 2.2.2.2 0.0.0.0 area 0
network 192.168.12.2 0.0.0.0 area 0
R3
interface
Loopback0
ip address 3.3.3.3 255.255.255.255
interface
Loopback1
ip address 13.13.13.13 255.255.255.255
interface
FastEthernet0/0
ip address 192.168.13.3 255.255.255.0
speed 100
full-duplex
R3#sh
run | sec router eigrp
router
eigrp 1
network 3.3.3.3 0.0.0.0
network 192.168.13.3 0.0.0.0
no auto-summary
router
bgp 1
network
3.3.3.3 mask 255.255.255.255
network 13.13.13.13 mask 255.255.255.255
neighbor 1.1.1.1 remote-as 1
neighbor 1.1.1.1 update-source Loopback0
no auto-summary
R4
interface
Loopback0
ip address 4.4.4.4 255.255.255.255
interface
Serial0/0
ip address 192.168.14.4 255.255.255.0
encapsulation ppp
clock rate 2000000
router
bgp 4
network
4.4.4.4 mask 255.255.255.255
neighbor 192.168.14.1 remote-as 1
no auto-summary
Verification
Now let us check basic relations and route advertisements before we do the redistribution
R1#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 1 FULL/DR 00:00:36 192.168.12.2 FastEthernet0/0
R1#sh ip route ospf
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/2] via 192.168.12.2, 00:38:13, FastEthernet0/0
R1#sh ip bgp summary
BGP router identifier 1.1.1.1, local AS number 1
BGP table version is 5, main routing table version 5
3 network entries using 360 bytes of memory
3 path entries using 156 bytes of memory
3/2 BGP path/bestpath attribute entries using 372 bytes of memory
1 BGP AS-PATH entries using 24 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 2 (at peak 2) using 64 bytes of memory
BGP using 976 total bytes of memory
BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
3.3.3.3 4 1 42 41 5 0 0 00:36:19 2
192.168.14.4 4 4 41 42 5 0 0 00:37:13 1
R1#sh ip bgp
BGP table version is 5, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
r>i3.3.3.3/32 3.3.3.3 0 100 0 i
*> 4.4.4.4/32 192.168.14.4 0 0 4 i
*>i13.13.13.13/32 3.3.3.3 0 100 0 i
R2#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/BDR 00:00:39 192.168.12.1 FastEthernet0/0
R2#sh ip route ospf
R2#
R3#sh ip bgp summary
BGP router identifier 3.3.3.3, local AS number 1
BGP table version is 3, main routing table version 3
3 network entries using 360 bytes of memory
3 path entries using 156 bytes of memory
3/1 BGP path/bestpath attribute entries using 372 bytes of memory
1 BGP AS-PATH entries using 24 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 1) using 32 bytes of memory
BGP using 944 total bytes of memory
BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
1.1.1.1 4 1 41 42 3 0 0 00:36:40 1
R3#sh ip bgp
BGP table version is 3, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 3.3.3.3/32 0.0.0.0 0 32768 i
* i4.4.4.4/32 192.168.14.4 0 100 0 4 i
*> 13.13.13.13/32 0.0.0.0 0 32768 i
R4#sh ip bgp summary
BGP router identifier 4.4.4.4, local AS number 4
BGP table version is 4, main routing table version 4
3 network entries using 360 bytes of memory
3 path entries using 156 bytes of memory
3/2 BGP path/bestpath attribute entries using 372 bytes of memory
1 BGP AS-PATH entries using 24 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 1) using 32 bytes of memory
BGP using 944 total bytes of memory
BGP activity 3/0 prefixes, 3/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.14.1 4 1 42 41 4 0 0 00:37:42 2
R4#sh ip bgp
BGP table version is 4, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 3.3.3.3/32 192.168.14.1 0 1 i
*> 4.4.4.4/32 0.0.0.0 0 32768 i
*> 13.13.13.13/32 192.168.14.1 0 1 i
So , all is functioning normal , now let us do one way redistribution from BGP into OSPF on R1 , R2 should according to the rule we mentioned above receive only 4.4.4.4/32 (which is the prefix learned via eBGP)
R1(config)#router ospf 1
R1(config-router)#redistribute bgp 1 subnets
R2#sh ip route ospf
4.0.0.0/32 is subnetted, 1 subnets
O E2 4.4.4.4 [110/1] via 192.168.12.1, 00:00:10, FastEthernet0/0
Which is true, we cannot see the 13.13.13.13/32 prefix which is learned via iBGP, now let us add the hidden command
R1(config-router)#router bgp 1
R1(config-router)#bgp redistribute-internal
R2#sh ip route ospf
4.0.0.0/32 is subnetted, 1 subnets
O E2 4.4.4.4 [110/1] via 192.168.12.1, 00:00:51, FastEthernet0/0
13.0.0.0/32 is subnetted, 1 subnets
O E2 13.13.13.13 [110/1] via 192.168.12.1, 00:00:03, FastEthernet0/0
And yes, this command also takes the iBGP learned routes and redistributes them
And we can see the command as well in the show running configuration
R1#sh run | sec router bgp
router bgp 1
no synchronization
bgp log-neighbor-changes
bgp redistribute-internal
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 update-source Loopback0
neighbor 192.168.14.4 remote-as 4
no auto-summary
