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Blackhole routing for eBGP peer interconnection

Latest reply: Sep 28, 2018 15:46:05 2804 2 0 0 0


Hello everyone! As a local enterprise, you will have to establish a company network and most likely you will need to interconnect your network with one or more ISPs. The most common case is interconnecting by using a eBGP session between your network edge device and the ISP PE device.

Let’ consider the topology below:



In this topology AS 20 is the Enterprise network and the two other ASes (10 and 30) belong to two different ISPs.

Problems start appearing when I try to advertise certain routing information to the ISPs. For this example I will try to advertise prefix to both eBGP peers. For this I will first need to add the network command in BGP view as below:


bgp 20

 network 24


For BGP to advertise this prefix to its peers I also need to add a static route for this prefix:


ip route-static 24 GigabitEthernet 2/0/0


Right not the prefix will be advertised but yet another problem appears. In AS 20 i only use half of the /24 range, the rest of it being reserved for future expansions. This being the case whenever I receive packets destined to unused ip address from the advertised range I would like Router B to drop these packets, thus eliminating any security threat (e.g. DDoS attacks).

To accomplish this I need to modify the static route to a blackhole one so I can be sure that any packet with a non-existent destination will be dropped.

The configuration to modify the static route is below:


undo ip route-static 24 GigabitEthernet 2/0/0

ip route-static 24 Null 0


After appling this configuration I can be sure that all security threats have been eliminated and I have a full functioning network.

This is what I want to talk about/share with you today, thank you!


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Created Mar 5, 2014 02:33:19

thanks for your share.
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Author Created Sep 28, 2018 15:46:05

Good scenario to interconnect your network with one or more ISPs
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