BGP Aggregate AS-SET

(Rene Molenaar) #1

This topic is to discuss the following lesson:

(Mohammad Hasanuz Zaman) #2

Hi Rene,
Just to be confirm , If we put the command aggregate-address 172.16.0.0 255.255.0.0 summary-only as-set on R1 then R2/R3 also get the prefix & discard based on as path , right ?Thanks

br//zaman

(Rene Molenaar) #3

Hi Zaman,

If you add as-set then the AS numbers of the prefixes are included so if there is a link between R2/R4 and R3/R4 and they receive this aggregate, they will drop it because they see their own AS number yes.

Rene

(Mohammad W) #4

Dear Rene,

If we set community for the aggregate-address and send this to eBGP speaker, on eBGP speaker can we see community for this aggregate-address.

//BR
Waqar

(bahri a) #5

Hi Rene
is there a incorrect that is the As name.
where is the AS 3 ,in my opinion R3 will be in the AS 3

1 Like
(Lazaros Agapides) #6

Hello Bahri

Thanks for catching that! I’ve informed Rene and he will fix it.

Thanks again!

Laz

(bahri a) #7

Hello Laz
thanks all
i m lucky because if laz is here no problem

1 Like
(Rene Molenaar) #8

It’s fixed now, thanks for reporting!

(Juan C) #9

I’m trying this exercise using 3 routers. R1-R2 iBGP peers, and R2-R3 eBGP peers.
i’ve configured a loopback interface on R1, 10.10.10.10/32 and on R2 i want to aggregate that /32 network in a /24 to R3 using the “aggregate-address 10.10.10.0 255.255.255.0” cli conf but i get this error ::
% BGP: Incorrect network or mask configurated

I’ve also tried with 255.0.0.0 and i get the same error on R2

Also i’ve checked with “show ip bgp” on R2 and the 10.10.10.10/32 is correctly injected in BGP table.

(Lazaros Agapides) #10

Hello Juan

In order to use the aggregate-address command to send an aggregate of 10.10.10.0/24, the corresponding loopback with an IP address within that range must be configured on the same router itself. The router will check your command against the IP addresses on the interfaces on the device and not against the BGP table. The problem is not the subnet mask, but the IP address that is not on a local interface.

Without having actually implemented the lab, my feeling is that If you want to issue the aggregate command, do so in R1. Try it out and let us know your results!

Laz

(Staut S) #11

So…the aggregate-address command without summary-only option can only summarize the local IP addresses (like BGP auto-summary) as Laz mentioned and aggregate-address summary-only can advertise a summary of BGP learned routes (this is what R1 does in the lesson)?
If this is the case can you please add a note in the lesson?

Also to be picky (again) can you please update the lesson picture with the IP addresses (though the configuration pattern is clear)?

Many thanks,
Stefanita

(Rene Molenaar) #12

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 :slight_smile:

Rene

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(Staut S) #13

This information is helpfull. Many thanks!

1 Like