Question about prefix list

Randy randy_94108 at yahoo.com
Wed Feb 1 22:13:38 CST 2012


Ann,
the commas not withstanding, the le/ge operands as applicable to prefix-lists simply mean "less-than or equal-to" or greater-than or "equal-to" wrt netmasks in CIDR speak.

In you prefix-list below, the le operand means -
allow following ranges:

/22,/23,/24 deny all else
for the /21
it means allow /21 thru /24

Anything without an operand means an exact-match(permit/deny)

Homework for you:

What do the following do:

1) ip prefix-list foo deny 0.0.0.0/0 le32
2) ip prefix-list foo permit 0.0.0/0 le 32

Understand the above and you will understand how operands work in prefix-lists.
./Randy


--- On Wed, 2/1/12, Ann Kwok <annkwok80 at gmail.com> wrote:

> From: Ann Kwok <annkwok80 at gmail.com>
> Subject: Question about prefix list
> To: nanog at nanog.org
> Date: Wednesday, February 1, 2012, 6:32 AM
> Hi
> 
> I read this prefix list.
> 
> Can I know why there is "le 24" after network block in /22
> and /21
> 
> Why don't have "le 24" after /24?
> 
> I also saw another prefix list before. They use "le 32"
> instead of  "le 24"
> 
> What are their different?
> 
> ip prefix-list prefix-filter-as100 seq 10 permit
> 202,168.136.0/22 le 24
> ip prefix-list prefix-filter-as100 seq 20 permit
> 202,22.92.0/22 le 24
> ip prefix-list prefix-filter-as100 seq 30 permit
> 202,21.148.0/22 le 24
> ip prefix-list prefix-filter-as100 seq 40 permit
> 203,178.88.0/21 le 24
> ip prefix-list prefix-filter-as100 seq 50 permit
> 178.88.74.0/24
> 
> Thank you so much
> 



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