Here we are going to learn and understand
about the Network Statement.
R1#sh ip route ospf
150.2.0.0/32 is subnetted, 1 subnets
O
150.2.2.2 [110/2] via 155.1.123.2, 01:08:54, FastEthernet2/0
150.3.0.0/32 is subnetted, 1 subnets
O
150.3.3.3 [110/2] via 155.1.123.3, 01:08:54, FastEthernet2/0
R1#sh ip route connected
155.1.0.0/24 is subnetted, 2 subnets
C
155.1.16.0 is directly connected, Serial1/0
C
155.1.123.0 is directly connected, FastEthernet2/0
150.1.0.0/24 is subnetted, 1 subnets
C
150.1.1.0 is directly connected, Loopback0
Here am going to publish this 150.1.1.0/24,
150.2.2.0/24 and 150.3.3.0/24 network in
BGP. So lets do it.
R1#sh ip bgp regexp ^$
BGP table version is 19, local router ID is
150.1.1.1
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
*> 150.1.1.0/24 0.0.0.0 0 32768 i
Amazed only 150.1.1.0/24 network is
advertising to others peers but not the other network but why??
Because the bgp network statement mask
should match the network in the routing table.
Lets have a look on network statement under
the bgp section.
R1#sh run | s router bgp
router bgp 100
no
synchronization
bgp
log-neighbor-changes
network 150.1.1.0 mask 255.255.255.0
network 150.2.2.0 mask 255.255.255.0
network 150.3.3.0 mask 255.255.255.0
neighbor iBGP_Peer peer-group
neighbor iBGP_Peer remote-as 100
neighbor iBGP_Peer update-source Loopback0
neighbor 150.2.2.2 peer-group iBGP_Peer
neighbor 150.3.3.3 peer-group iBGP_Peer
neighbor 155.1.16.6 remote-as 600
no
auto-summary
And now cross check with our routing table.
You will now understand 150.1.1.0/24 is listed but 150.2.2.2/32 and
150.3.3.3/32 network is listed
To overcome this we can do two different
things. Whether change the network statement or publish the correct network
statement into the ospf domain.
Here am going to change the ip ospf
network.
R2(config)#int lo 0
R2(config-if)#ip ospf network
point-to-point
R3(config)#int lo 0
R3(config-if)#ip ospf network
point-to-point
Now lets look into BGP routing table.
R1#sh ip bgp regexp ^$
BGP table version is 24, local router ID is
150.1.1.1
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
*> 150.1.1.0/24 0.0.0.0 0 32768 i
*> 150.2.2.0/24 155.1.123.2 2 32768 i
*> 150.3.3.0/24 155.1.123.3 2 32768 I
See we got all the network which we
published in BGP. But if u take a deep look in the above network you are getting metric value as non zero.
But how bgp got metric value as we knew we
didn't configure any metric.
The answer is we got the metric from the
IGP.
R1#sh ip route 150.2.2.2
Routing entry for 150.2.2.0/24
Known via "ospf 1", distance 110, metric 2, type intra
area
Advertised by bgp 100
Last update from 155.1.123.2 on FastEthernet2/0, 00:15:35 ago
Routing Descriptor Blocks:
*
155.1.123.2, from 150.2.2.2, 00:15:35 ago, via FastEthernet2/0
Route metric is 2, traffic share count is 1
R1#sh ip route 150.3.3.3
Routing entry for 150.3.3.0/24
Known via "ospf 1", distance 110, metric 2, type intra
area
Advertised by bgp 100
Last update from 155.1.123.3 on FastEthernet2/0, 00:15:48 ago
Routing
Descriptor Blocks:
*
155.1.123.3, from 150.3.3.3, 00:15:48 ago, via FastEthernet2/0
Route metric is 2, traffic share count is 1
The metric(MED) field is copied with the
IGP metric value.
Redistribute Statement
Now we are going to redistribute the
eigrp route into bgp network o R4.
R4(config)#router bgp 400
R4(config-router)#redistribute eigrp 1
R4(config-router)#do sh ip bgp regex ^$
BGP table version is 48, local router ID is
150.4.4.4
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
*> 4.1.0.0/24 0.0.0.0 0 32768 i
*> 4.2.0.0/24 0.0.0.0 0 32768 i
*> 4.3.0.0/24 0.0.0.0 0 32768 i
*> 44.4.4.0/24 0.0.0.0 0 32768 ?
*> 44.5.4.0/24 0.0.0.0 0 32768 ?
*> 44.6.4.0/24 0.0.0.0 0 32768 ?
*> 150.4.4.0/24 0.0.0.0 0 32768 ?
*> 150.5.5.0/24 155.1.45.5 2297856 32768 ?
*> 155.1.45.0/24 0.0.0.0 0 32768 ?
See if we just redistribute the eigrp it
will redistribute all the prefixes learned via eigrp and plus the eigrp enabled
interface. To over come this am going to create route map and going to
advertise only the 44.x.x.x/24 network.
R4(config)#ip prefix-list 44 permit 44.4.4.0/24
R4(config)#ip prefix-list 44 permit
44.5.4.0/24
R4(config)#ip prefix-list 44 permit
44.6.4.0/24
R4(config)#route-map 44_network
R4(config-route-map)#match ip address
prefix-list 44
R4(config)#router bgp 400
R4(config-router)#redistribute eigrp 1
route-map 44_network
Now lets check the router R4 what all route
they are generating.
R4#sh ip bgp regexp ^$
BGP table version is 33, local router ID is
150.4.4.4
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
*> 4.1.0.0/24 0.0.0.0 0 32768 i
*> 4.2.0.0/24 0.0.0.0 0 32768 i
*> 4.3.0.0/24 0.0.0.0 0 32768 i
*> 44.4.4.0/24 0.0.0.0 0 32768 ?
*> 44.5.4.0/24 0.0.0.0 0 32768 ?
*> 44.6.4.0/24 0.0.0.0 0 32768 ?
R4#sh ip bgp | in \?
Origin codes: i - IGP, e - EGP, ? -
incomplete
*> 44.4.4.0/24 0.0.0.0 0 32768 ?
*> 44.5.4.0/24 0.0.0.0 0 32768 ?
*> 44.6.4.0/24 0.0.0.0 0 32768 ?
? Symbol denotes that the network is
redistributed into bgp.
