What is the use of null route

[rangap26.]

when i say the configuration in the router When we advertise the subnets directly in BGP using network command

we are using a static route of the same full subnet pointing to NULL 0

Can any one Help me understanding this concept of NULL 0 Routing

[ricardo.josephs]

Hi,

I know this is an old post, but what happens if the network to the null interface, is for NAT?  Will this traffic be dropped?  Or the NAT will be accomplished?  I have a public segment I want to use to NAT on an ASA, and advertise this network to the ISP. I understood  the creating the route to the null interface will let me advertise the network over BGP to the ISP, but if I need to use this segment to NAT on my ASA for services, will this incoming traffic be dropped?

Bet regards

Ricardo

[Richard Burts]

Ricardo

This is an old post and it covered several ways that null route could be in the routing table (could be the result of route summarization, could be a floating route (static route applied with higher AD to be used when dynamic route is not available) etc. It is not clear to me in your question which type of null route this would be. Can you clarify this?

Other parts of your question are also not clear. You mention "a public segment I want to use to NAT" If it is a public segment then why would you want to nat it? It would seem to make more sense if it were a private segment to be nat. Can you clarify this?

[arsalanali]

Explained Well!

[Richard Burts]

Thank you. I appreciate the compliment.  This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

[tomcruse44217]

Hi there, The concept of using a Null 0 route in BGP is a bit complex, but essentially it's a technique used to prevent traffic from getting forwarded to destinations that are not intended to receive traffic. By configuring a Null 0 route for a specific subnet, any traffic that is destined for that subnet will be dropped by the router, effectively blocking any unwanted traffic from entering the network. This technique is often Use in combination with the network command in BGP, as you mentioned, to advertise the subnet to other routers in the network. It's a useful way to ensure that only legitimate traffic is allowed into the network. I hope this helps in understanding the concept of Null 0 routing. Let me know if you have any further questions or concerns.