Prefix-list

[star1]

Hello all,

I am trying to redistribute static route into the ospf and use prefix-list.

I have 20 static routes need to be advertised through the prefix-list and all the subnets are have different subnet masks. for example they have /8, /24, /26, , /27, /28, /21, /32

I am bit confused about how to use le and ge at the end of the prefix-list.

for example if i write,

ip prefix-list static-ospf seq 5 permit 127.0.0.0/8 le 24 is that mean everything from /8,to /24 is permitted to be advertised? or do i have to use ip prefix-list static-ospf seq 5 permit 127.0.0.0/8 ge 24.

Note: This changes will be happening on Nexus 5k.

I am confused not sure if i should be use LE or GE.

can someone help please? thank you.

[rais]

permit 127.0.0.0/8 le 24

means to advertise subnets of length 8-24

127.0.0.0/8 ge 24

means to advertise subnets of length 24-32

I believe you are simply using 127/8 as an example...as this is the subnet on each IP device.

HTH.

[Cristian Matei · Accepted solution]

Hi,

     Here's your options (le stands for less or equal to, while ge stands for greater than or equal to):

              - 192.168.10.0/24 will match on the 192.168.10.x prefix with a prefix-length/mask of exactly /24

              - 192.168.10.0/24 le 26 will match on the 192.168.10.x prefix with a prefix-length/mask between /24 and /26, which means /24, or /25, or /26

              - 192.168.10.0/24 ge 26 will match on 192.168.10.x prefix with a prefix-length/mask between /26 and /32, which means /26, or /27, or /28, or /29, or /30, or /31, or /32

Regards,

Cristian Matei.

[star1]

Hello All,

Thanks to all of you for the quick answers. Now is make more senses.

However, I'me still confused that which value I should be using?

For example, le, ge or eq? I understand the difference between them as you guys explained but in my case not sure which one i should use.

In my understanding, I should be using the eq because this will matches the static routes. I'm I right please?

Thank you guys. 

[Georg Pauwen]

Hello,

'eq' will match the exact static route, while 'le' and 'ge' will match any route with a lesser/equal and/or greater/equal mask, so you might inadvertently block or allow routes you do not want to block or allow.

I would use 'eq'...although that makes your prefix list longer.

[Georg Pauwen]

Hello,

on a side note, if you really just want to block specific routes, you could use sequence numbers and match on the exact subnet and mask:

ip prefix-list PREFIXES_ALLOWED seq 5 permit x.x.x.x/8 eq 8
ip prefix-list PREFIXES_ALLOWED seq 10 permit x.x.x.x/21 eq 21
ip prefix-list PREFIXES_ALLOWED seq 15 permit x.x.x.x/24 eq 24
ip prefix-list PREFIXES_ALLOWED seq 20 permit x.x.x.x/26 eq 26
ip prefix-list PREFIXES_ALLOWED seq 25 permit x.x.x.x/27 eq 27
ip prefix-list PREFIXES_ALLOWED seq 30 permit x.x.x.x/28 eq 28
ip prefix-list PREFIXES_ALLOWED seq 35 permit x.x.x.x/32 eq 32

etc.

etc.

etc.