Hello Stefanita,
The aggregate-address command can summarize anything that is in the BGP table. The summary-only option defines whether you advertise the summary route next to the regular route or only the summary route. Quick example:
R4#show run int l4
Building configuration...
Current configuration : 69 bytes
!
interface Loopback4
ip address 123.123.123.123 255.255.255.0
end
R4#show run | section bgp
router bgp 4
bgp log-neighbor-changes
network 123.123.123.0 mask 255.255.255.0
neighbor 192.168.14.1 remote-as 1
123.123.123.0/24 shows up on R1 like this:
R1#show ip bgp | include 123
*> 123.123.123.0/24 192.168.14.4 0 0 4 i
And R1 forwards it to R2 and R3. Here’s R2:
R2#show ip bgp | include 123
*> 123.123.123.0/24 192.168.12.1 0 1 4 i
Let’s summarize it:
R1(config)#router bgp 1
R1(config-router)#aggregate-address 123.123.0.0 255.255.0.0
Now it shows up on R2 (and R3) like this:
R2#show ip bgp | include 123
*> 123.123.0.0/16 192.168.12.1 0 0 1 i
*> 123.123.123.0/24 192.168.12.1 0 1 4 i
Let’s try the summary-only command:
R1(config)#router bgp 1
R1(config-router)#aggregate-address 123.123.0.0 255.255.0.0 summary-only
And it shows up like this:
R2#show ip bgp | include 123
*> 123.123.0.0/16 192.168.12.1 0 0 1 i
Does this help?
I updated the picture btw to add the network addresses and IP addresses
Rene