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I don't know what I should be using for this or how I should go about it.

In my lab where I am testing out the BGP configs that I've learned I want my ISP topology to have a summary prefix for the Customer to see. I am peering with eBGP to the customer with 3 links. 8.1.7.0 /30 1 - 20 are allocated to this Customer for their WAN links.

ISP has BGP built over an OSPF underlay and is peering with loopbacks

Customer is using EIGRP for IGP
On the Customer's ASBRs the only advertised address is 17.1.2.0 /24
The addresses is aggregated after being redistributed into BGP

These are my configs for BGP on the ISP CE device

router bgp 65001
 bgp log-neighbor-changes
 network 8.1.5.0 mask 255.255.255.252
 network 8.1.7.0 mask 255.255.255.252
 network 8.8.8.2 mask 255.255.255.255
 network 17.1.2.0 mask 255.255.255.252
 neighbor 8.1.7.2 remote-as 65002
 neighbor 8.8.8.3 remote-as 65001
 neighbor 8.8.8.3 update-source Loopback0

I think I can remove the #network 17.1.2.0 command since I aggregated the route on another BGP device

When it comes to summarizing all my 8.0.0.0 /8 prefixes to AS65002 I can't figure out how. I'm pretty new to using route-maps and prefix lists and that's what I was trying to use for this project.

Lab setup

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  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
    – Ron Maupin ♦
    Commented Dec 31, 2020 at 4:33

1 Answer 1

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7

This appears to be a Cisco router. Cisco has the aggregate-address command.

You can advertise the aggregate address and all the individual addresses:

aggregate-address 8.0.0.0 255.0.0.0

or only the aggregate address:

aggregate-address 8.0.0.0 255.0.0.0 summary-only

As long as even one prefix in the aggregate is in the routing table, the aggregate will be advertised. This will also create a route to Null0.

Cisco maintains many documents about such things. For example Understanding Route Aggregation in BGP.

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  • It is Cisco, and this is what i used in the first place. However, when I had these configured on the edge devices of the ISP it broke my Route reflectors and while pinging across the ISP I received "unreachable" responses when pinging from within AS65002. This was done from a router only running eigrp. The packets reached the device that had the aggregation command on it then it dropped.
    – Isaac Bill
    Commented Jun 19, 2019 at 17:12
  • Then you need to edit your question to provide full router configurations. BGP will not advertise any prefix not already in the routing table, except in the case of an aggregate prefix, for which it adds the route to Null0.
    – Ron Maupin ♦
    Commented Jun 19, 2019 at 17:16
  • 1
    @IsaacBill, can you please edit the question to include full configuration including the RR along with the live troubleshooting.
    – ditrapanij
    Commented Jun 19, 2019 at 21:09

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