[FROG] What 'ge' 'le' really means ?

[Rudy Rucker]

It's counter-intuitive.  ge 24 means:

  /8 /16 /13 /23 etc.

le 24  or 'less than or equal' means all CINR values that are 
numerically BIGGER.

   /24 /28 /32 /28 etc.

So why 'le' and 'ge'?

Because a /22 (1024 ips) defines a LARGER network than a /30 (only 4 ips)


Where did all this math come from?  What are bits?  Let's take 
4.2.2.0/24 as an example:
The Mask or /24 value states how many bits in the IP address define the 
network.  If your mask is 24 bits, and all IPv4 addresses is 32 bits (or 
2^32) then the number of IPs in your network is:
    2^ (32 - 24) = 2 ^ 8 = 256

Here is a list that filters all BGP prefixes that are for tiny blocks of 
IPs... you can limit your BGP session to only allow blocks that have a 
minimum of 256 IPs.  In other words, anything "equal to or Greater" than 
256 IPs:

ip prefix-list bgpFilter seq 10 permit 0.0.0.0/0 ge 24
ip prefix-list bgpFilter seq 99 deny any


Hope that helps,

Rudy


On 2/15/20 11:36 PM, Daniel Corbe wrote:
> typo in my reply.  When I said ip prefix-list test_ipv4_1_1 seq 10
> permit 192.18.8.0/24 ge 32 I meant ip prefix-list test_ipv4_1_1 seq 10
> permit 192.18.8.0/24 le 32
>
> On Sun, Feb 16, 2020 at 2:35 AM Daniel Corbe <daniel at corbe.net> wrote:
>> Simon,
>>
>> If you're trying to specify a maximum prefix length of 32, you need
>> the le keyword.
>>
>> ip prefix-list test_ipv4_1_1 seq 10 permit 192.18.8.0/24 ge 32 means
>> "accept any prefix length for 192.18.8.0 between 24 and 32 bits"
>>
>> IE ip prefix-list test_ipv4_1_1 seq 10 permit <subnet>/<shortest
>> prefix match> le <longest prefix match>
>>
>> On Sat, Feb 15, 2020 at 5:47 PM Simon Jones <batmanustc at gmail.com> wrote:
>>> Hi all,
>>>
>>> In this command:
>>>> gyw-229(config)# ip prefix-list test_ipv4_1_1 seq 10 permit 192.18.8.0/24 ge 24
>>>> % Invalid prefix range for 192.18.8.0/24, make sure: len < ge-value <= le-value
>>>> gyw-229(config)# ip prefix-list test_ipv4_1_1 seq 10 permit 192.18.8.0/24 ge 25
>>> we see 'ge' means greater.
>>>
>>> But in doc:
>>>> ge command specifies prefix length. The prefix list will be applied if the
>>>> prefix length is greater than or equal to the ge prefix length
>>>
>>> So what's 'ge' really means?
>>> And how to set equal command? Set equal command using 'ge xxx le xxx' before, but if 'ge' means greater, how to set? Use this command?
>>>> ip prefix-list test_ipv4_1_1 seq 10 permit 192.18.8.0/32
>>>
>>> ----
>>> Simon Jones
>>> _______________________________________________
>>> frog mailing list
>>> frog at lists.frrouting.org
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