3.7.b Implement and troubleshoot IBGP and EBGP

3.7.b [i] EBGP, IBGP

from: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800945ff.shtml

Because there is no component route (no classful route or subnet route ) in the R101 IP routing table, the network 6.0.0.0 in not installed in the BGP table. The minimum requirement for a prefix configured under the network command to be installed in a BGP table is to have a component route in the IP routing table. So make sure that R101 has a component route for network 6.0.0.0/8 either by learning it through IGP or through static configuration

null0 can be used to advertise a route in bgp when the so called component route is missing, or the component route is advertised by the igp and null0 will not be necessary… in english please… can you hear me in the back…

note the mask on the interface and then note the mask in bgp for 10.1.1.1

R1#sh run int lo1
Building configuration…

Current configuration : 94 bytes
!
interface Loopback1
ip address 10.1.1.1 255.255.255.0
ip ospf network point-to-point

router bgp 65001
bgp log-neighbor-changes
network 10.1.0.0 mask 255.255.0.0

that dog don’t hunt… look at the route table…

R1#sh ip route | b Gate
Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
C        1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O        2.2.2.2 [110/65] via 200.1.1.2, 00:50:53, Serial2/0
10.0.0.0/8 is variably subnetted, 3 subnets, 3 masks
C        10.1.1.0/24 is directly connected, Loopback1
L        10.1.1.1/32 is directly connected, Loopback1
O        10.2.1.0/24 [110/65] via 200.1.1.2, 00:03:54, Serial2/0
200.1.1.0/24 is variably subnetted, 2 subnets, 2 masks
C        200.1.1.0/24 is directly connected, Serial2/0
L        200.1.1.1/32 is directly connected, Serial2/0

the bgp network being advertised is a /16 whereas the best that the route table is doing is a /24… no component route from igp… NO SUBNET ROUTE…

here’s where we can use null0 to do the dirty…

R1(config)#ip route 10.1.0.0 255.255.0.0 null0
R1(config)#end
R1#
*Mar 13 14:04:48.943: %SYS-5-CONFIG_I: Configured from console by console
R1#sh ip bgp
Network          Next Hop            Metric LocPrf Weight Path
*>  10.1.0.0/16      0.0.0.0                  0         32768 i

problem solved… or make the interface and the network match…

R1(config-if)#ip add 10.1.1.1 255.255.0.0
R1(config-if)#end
R1#cl
*Mar 13 14:09:16.191: %SYS-5-CONFIG_I: Configured from console by console
R1#clear ip bgp *
R1#
*Mar 13 14:09:22.875: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Down User reset
*Mar 13 14:09:22.875: %BGP_SESSION-5-ADJCHANGE: neighbor 2.2.2.2 IPv4 Unicast topology base removed from session  User reset
*Mar 13 14:09:23.511: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Up
R1#sh ip bgp
R1#sh ip bgp
R1#sh ip bgp
R1#sh ip bgp
R1#sh ip bgp (and finally)
R1#sh ip bgp
BGP table version is 5, local router ID is 10.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i – IGP, e – EGP, ? – incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network          Next Hop            Metric LocPrf Weight Path
*>  10.1.0.0/16      0.0.0.0                  0         32768 i
*>  10.2.0.0/16      2.2.2.2                  0             0 65002 i

R1#sh ip route | b Gate
Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
C        1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O        2.2.2.2 [110/65] via 200.1.1.2, 01:07:27, Serial2/0
10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C        10.1.0.0/16 is directly connected, Loopback1
L        10.1.1.1/32 is directly connected, Loopback1
       10.2.0.0/16 [20/0] via 2.2.2.2, 00:02:54
200.1.1.0/24 is variably subnetted, 2 subnets, 2 masks
C        200.1.1.0/24 is directly connected, Serial2/0
L        200.1.1.1/32 is directly connected, Serial2/0