any dangers of filtering every /24 on full internet table to preserve FIB space ?

Mark Tinka mark at
Mon Oct 10 15:37:26 UTC 2022

On 10/10/22 16:58, Edvinas Kairys wrote:

> Hello,
> We're considering to buy some Cisco boxes - NCS-55A1-24H. That box has 
> 24x100G, but only 2.2mln route (FIB) memory entries. In a near future 
> it will be not enough - so we're thinking to deny all /24s to save the 
> memory. What do you think about that approach - I know it could 
> provide some misbehavior. But theoretically every filtered /24 could 
> be routed via smaller prefix /23 /22 /21 or etc. But of course it 
> could be a situation when denied /24 will not be covered by any 
> smaller prefix.

I wouldn't bank on that.

I am confident I have seen /24's with no covering route, more so for PI 
space from RIR's that may only be able to allocate a /24 and nothing 

It would be one heck of an experiment, though :-).


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