🚨 The #1 BGP Configuration Mistake

...I Keep Seeing Network Engineers Make

Have you ever configured a BGP network statement and… nothing happens?

The routes aren't advertised, and you never receive the desired traffic.

Most of the time, this issue stems from one subtle quirk in how BGP works.

Unlike other routing protocols, the BGP network command requires an exact match in the routing table, including the prefix length, for a route to be advertised. It will not advertise more specific subnets of the network.

There are several ways to fix this:

1️⃣ Add exact network statements for each subnet:

network [ip address] [subnet mask]

BGP will then advertise those subnets directly.

2️⃣ Include the larger route in your IGP.

If the aggregate route appears in the routing table, BGP can advertise it.

3️⃣ Configure a static null route for the larger prefix.

ip route [ip address] [mask] Null0

This adds the route to the routing table so BGP can advertise it.

⚠️ Caution: Traffic to that prefix will be dropped unless a more specific route exists.

4️⃣ Redistribute routes into BGP instead of using the network command.

This avoids the exact match requirement entirely. You can filter redistribution to control which routes BGP advertises.

💬 Have you encountered this issue before? How did you fix it?