Configure BGP Route Summary

Network Requirements

• Set up OSPF neighbors between Device1 and Device3, and configure Device3 to advertise routes 100.1.0.0/24 and 100.2.0.0/24 to Device1.
• Set up EBGP neighbors between Device1 and Device2.
• On Device1, aggregate routes 100.1.0.0/24 and 100.2.0.0/24 into route 100.0.0.0/14 and advertise the aggregated route to Device2.

Network Topology

Figure 12–5 Networking for configuring BGP route summary

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 Device1.

#Configure Device3.

#Query the routing table of Device1.

Device1#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 100.1.0.0/24 [110/2] via 2.0.0.2, 00:00:24, vlan3 
O 100.2.0.0/24 [110/2] via 2.0.0.2, 00:00:24, vlan3 

According to the routing table, Device1 has learnt routes 100.1.0.0/24 and 100.2.0.0/24 advertised by Device3.

Step 4: Configure BGP.

#Configure Device1.

#Configure Device2.

#On Device1, check the BGP neighbor status.

Device1#show ip bgp summary  
BGP router identifier 1.0.0.1, 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      2            2             2       0     0      00:00:42       0 

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

Step 5: Configure BGP route summary.

Two solutions are available to satisfy network requirements.

Solution 1: Configure an aggregated static route that is targeted at null0 to introduce the aggregated static route to BGP.

#Configure Device1.

Check the result.

#Query the BGP routing table of Device1.

Device1#show ip bgp                     
BGP table version is 2, local router ID is 10.0.0.1 
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]*> 100.0.0.0/14	0.0.0.0               32768                      i 

The aggregated route 100.0.0.0/14 has been generated in the BGP routing table of Device1.

#Query the routing table of Device2.

Device2#show ip bgp  
BGP table version is 3, local router ID is 20.0.0.1 
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]*> 100.0.0.0/14       1.0.0.1           0        0        100      i 
 
Device2#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	100.0.0.0/14 [20/0] via 1.0.0.1, 01:39:30, vlan2 

Device2 has successfully learnt the aggregated route 100.0.0.0/14 that has been advertised by Device1.

Solution 2: First introduce common routes into BGP, and then run the aggregate-address command to aggregate the routes.

#Configure Device1.

Check the result.

#Query the BGP routing table of Device1.

Device1#show ip bgp                     
BGP table version is 2, local router ID is 10.0.0.1 
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]*> 100.0.0.0/14       0.0.0.0                                  32768  i
[B]s> 100.1.0.0/24       2.0.0.2               2                  32768  i
[B]s> 100.2.0.0/24       2.0.0.2               2                  32768  i

The aggregated route 100.0.0.0/14 has been generated in the BGP routing table of Device1.

#Query the routing table of Device2.

Device2#show ip bgp  
BGP table version is 3, local router ID is 20.0.0.1 
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]*> 100.0.0.0/14       1.0.0.1               0        0        100      i 
 
Device2#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 100.0.0.0/14 [20/0] via 1.0.0.1, 01:39:30, vlan2 

Device2 has successfully learnt the aggregated route 100.0.0.0/14 that has been advertised by Device1.

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  When the aggregate-address command is used to aggregate routes, if the extended command is configured, the device advertises only the aggregated route; otherwise, both common routes and aggregated routes are advertised.

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