Configure BGP Confederation

Network Requirements

• Device2, Device3, Device4, and Device5 are in the same BGP AS 200. To reduce the number of IBGP full connections, they are divided into two different ASs in one BGP confederation.
• Set up EBGP neighbors between Device1 and Device2, and advertise route 100.0.0.0/24 to AS 200.

Network Topology

Figure 12–7 Networking for configuring a BGP confederation

Configuration Steps

Step 1: Configure the VLAN and join the interface to the corresponding VLAN. (Omitted)

Step 2: Configure the IP addresses of the interfaces. (Omitted)

Step 3: Configure OSPF so that loopback routes are reachable between devices.

#Configure Device2.

#Configure Device3.

#Configure Device4.

#Configure Device5.

#Query the routing table of Device2.

Device2#show ip route ospf 
Codes: C - Connected, L - Local, S - static, R - RIP, B - BGP, i-ISIS 
       U - Per-user Static route 
       O - OSPF, OE-OSPF External, M - Management, E - IRMP, EX - IRMP external 
 
O 4.0.0.0/24 [110/2] via 2.0.0.1, 00:02:42, vlan3 
               [110/2] via 3.0.0.1, 00:02:11, vlan4
O 30.0.0.1/32 [110/2] via 2.0.0.1, 00:02:32, vlan3
O 40.0.0.1/32 [110/2] via 3.0.0.1, 00:02:05, vlan4 

#Query the routing table of Device3.

Device3#show ip route ospf 
Codes: C - Connected, L - Local, S - static, R - RIP, B BGP, i-ISIS 
       U Per-user Static route 
       O - OSPF, OE-OSPF External, M - Management, E - IRMP, EX IRMP external 
 
O 3.0.0.0/24 [110/2] via 2.0.0.2, 00:03:24, vlan2 
               [110/2] via 4.0.0.2, 00:02:38, vlan3
O 20.0.0.1/32 [110/2] via 2.0.0.2, 00:03:24, vlan2
O 40.0.0.1/32 [110/2] via 4.0.0.2, 00:02:38, vlan3 

#Query the routing table of Device4.

Device4#show ip route ospf 
Codes: C - Connected, L - Local, S - static, R - RIP, B BGP, i-ISIS 
       U Per-user Static route 
       O - OSPF, OE-OSPF External, M - Management, E - IRMP, EX IRMP external 
 
O 2.0.0.0/24 [110/2] via 3.0.0.2, 00:03:42, vlan2 
               [110/2] via 4.0.0.1, 00:03:42, vlan3
O 20.0.0.1/32 [110/2] via 3.0.0.2, 00:03:42, vlan2
O 30.0.0.1/32 [110/2] via 4.0.0.1, 00:03:42, vlan3 

#Query the routing table of Device5.

Device5#show ip route ospf 
Codes: C - Connected, L - Local, S - static, R - RIP, B BGP, i-ISIS 
       U Per-user Static route 
       O - OSPF, OE-OSPF External, M - Management, E - IRMP, EX IRMP external 
 
O 2.0.0.0/24 [110/3] via 5.0.0.1, 00:00:03, vlan2
O 3.0.0.0/24 [110/2] via 5.0.0.1, 00:00:03, vlan2
O 4.0.0.0/24 [110/2] via 5.0.0.1, 00:00:03, vlan2
O 20.0.0.1/32 [110/3] via 5.0.0.1, 00:00:03, vlan2
O 30.0.0.1/32 [110/3] via 5.0.0.1, 00:00:03, vlan2
O 40.0.0.1/32 [110/2] via 5.0.0.1, 00:00:03, vlan2 

According to the routing table, Device2, Device3, and Device4 have learnt the routes of the loopback interfaces of each other.

Step 4: Configure BGP connections in a confederation.

Configure IBGP connections in a confederation.

#Configure Device2.

#Configure Device3.

#Configure Device4.

Configure EBGP connections in a confederation.

#Configure Device4.

#Configure Device5.

#On Device4, check the BGP neighbor status.

Device4#show ip bgp summary  
BGP router identifier 40.0.0.1, local AS number 65100 BGP table version is 2 
1 BGP AS-PATH entries 0 BGP community entries 
 
Neighbor    V AS          MsgRcvd MsgSent TblVer InQ OutQ   Up/Down      State/PfxRcd
5.0.0.2      4  65200    15          15          2        0     0        00:09:40       0 
20.0.0.1    4  65100     9           9            2        0     0        00:07:49       0 
30.0.0.1    4  65100     7           7            2        0     0        00:05:39       0  

IBGP neighbors have been set up between Device4 and Device2 and between Device4 and Device3, and EBGP neighbors have been set up between Device4 and Device5.

Step 5: Configure a BGP confederation.

#Configure Device1.

Configure an EBGP peer. The AS number of the peer is confederation as ID 200.

#Configure Device2.

Configure the BGP confederation ID to 200, and configure an EBGP peer. The peer AS number is 100.

#Configure Device3.

Configure the BGP confederation ID to 200.

#Configure Device4.

Configure the BGP confederation ID to 200, and configure the confederation to contain area 65100.

#Configure Device5.

Configure the BGP confederation ID to 200, and configure the confederation to contain area 65200.

Step 6: Check the result.

#On Device1, check the BGP neighbor status.

Device1#show ip bgp summary  
BGP router identifier 100.0.0.1, local AS number 100 BGP table version is 2 
1 BGP AS-PATH entries 0 BGP community entries 
 
Neighbor    V  AS       MsgRcvd MsgSent  TblVer  InQ OutQ Up/Down        State/PfxRcd
1.0.0.2      4  200      6            6             2         0    0       00:02:20       0 

EBGP neighbors have been successfully set up between Device1 and Device2.

#On Device5, query the route information.

Device5#show ip bgp  
BGP table version is 49, local router ID is 5.0.0.2 
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              S Stale 
Origin codes: i - IGP, e - EGP, ? - incomplete 
          Network          Next Hop      Metric LocPrf  Weight       Path 
[B]*> 100.0.0.0/24	20.0.0.1       0        100      0 (65100) 100 i 
 
 
Device5#show ip route bgp 
Codes: C - Connected, L - Local, S - static, R - RIP, B - BGP, i-ISIS 
       U - Per-user Static route 
       O - OSPF, OE-OSPF External, M - Management, E - IRMP, EX - IRMP external 
 
B	100.0.0.0/24 [200/0] via 20.0.0.1, 00:00:38, vlan2 

Device5 has successfully learnt route 100.0.0.0/24, and the next-hop property of the route keeps unchanged while the route is transmitted in the confederation. Device2, Device3, Device4, and Device5 belong to the same confederation, and full connections are not required. Device5 obtains external route information through Device4.