ip route summary with null0 static routes

[pannkakan_1]

Hi!

I'm having some issue with understanding how to solve a problem. I have three static addresses pointing to a ISP. I want to summarize these 3 addresses and add a null0 route to the summary address. Will that work?

For Example

ip route 192.183.4.0 255.255.255.0 10.0.0.1

ip route 192.183.97.0 255.255.255.0 10.0.0.1

ip route 192.183.159.48 255.255.255.0 10.0.0.1

ip route 192.183.0.0 255.255.0.0 null0

Is there any issue with this configuration?

Kind Regards,

[Diana Karolina Rojas]

If you configure all the four routes in your router, you will get this behavior:

When a packet come to the router with a destination address different to 192.183.4.0, 192.183.97.0 or 192.183.159.48 /24 but inside of the summarizated route It will drop the packet to avoid a routing loop, sending it to Null0 or "black hole" route. If another packet comes to the router with a destination address 192.168.1.1 (for example) that packet will go to the default route (only if you have one) and won't be dropped. What do you want to do exactly?

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Regards,

[pannkakan_1]

Thanks for your reply!

Yes I do have a default route. There was a demand from the higher up that we should have null0 on every network statement, so I thought about the example I previously posted about. At the moment we're not using null0 and we dont have any summarization of the networks.

[Jon Marshall]

It depends on your topology etc. but be very careful summarising in the way you have because as explained you could actually cut yourself off from remote networks. So in the example you give you do not presumably own all the 192.183.x.x networks that you do mention but are included in the summary ?

Jon

[pannkakan_1]

Yea I dont own them. Hm.. I dont know really what to do should I just add another statement after each ip route with a null0 also?

[Jon Marshall]

Do you know why they want this because it seems strange if you already have the routes with a valid next hop IP.

It's difficult to say more without understanding your topology and what it is you are trying to achieve.

Jon

[pannkakan_1]

I dont really know either! I will talkwith the others tomorrow and see if I come up with anything! Will let you guys know!

[Diana Karolina Rojas]

If you add Null0 routes you have to be careful, you have to take into acount that If you do not have an explicit route for a destination and an ip or network is inside the summarizated routes you will drop that packets and when you want to add another subnet to your network you have to consider this also, because you could leave that network without conection to your ISP.

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Regards,