From: naveen M S (navin.ms@gmail.com)
Date: Fri Mar 27 2009 - 20:37:57 ART
Raghav,
In brief, prefix-list has 2 parts.
1) Network part "1.1.1.1/8", where /8 how many bits to match in 1.1.1.1.
Only first 8 bits has to match "1". Rest ignored.
2) Subnet Mask part "ge 24 le 32", which says match prefixes whose mask ge
24 and le 32
Hence, 1.1.1.1/8 ge 24 le 32 would match any of the following:
a) 1.2.3.0 /24
b) 1.2.3.128 /26
c) 1.2.3.192 /28 etc .
This wouldn't match 1.2.0.0/16, 1.2.2.0/20 etc.
The second example, say 2.1.0.0 /16 ge 24 and le 26 would match any of
following:
a) 2.1.5.0 /24
b) 2.1.5.x /26
c) 2.1.5.y /26 etc.
It wouldn't match 2.1.5.x /27, 2.1.6.x /28, becoz the network part matches
but subnet mask part doesn't.
HTH,
Naveen.
And yes, the sequence numbers are added
On Fri, Mar 27, 2009 at 1:16 PM, Scott M Vermillion <
scott_ccie_list@it-ag.com> wrote:
> Bit of a belated response here but I've been pounding away on SP and
> getting further and further behind on my list traffic. Congrats to all you
> new CCIEs out there, BTW.
>
> You need some solid prefix-list theory under your belt (there are some
> great blog posts out there on the topic) but then you just need time on the
> CLI to see how things behave for yourself. You should realize right off the
> bat that if you specify a "/8" in the prefix part of your prefix-list, none
> of the bits in positions 9 thru 32 matter, so they should be all zeros in
> your command. The less obvious part is what happens to that 'le 32' you
> threw on the end there. It's basically inferred/encompassed by the 'ge'
> operator and so is redundant. IOS will politely and discretely ignore your
> prefix-list faux pas.
>
> Rack1R1(config)#ip prefix blah seq 5 permit 1.1.1.1/8 ge 24 le 32
> Rack1R1(config)#do sh ip prefix
> ip prefix-list blah: 1 entries
> seq 5 permit 1.0.0.0/8 ge 24
> Rack1R1(config)#ip prefix blah seq 10 permit 2.0.0.0/8 ge 24 le 31
> Rack1R1(config)#do sh ip prefix
> ip prefix-list blah: 2 entries
> seq 5 permit 1.0.0.0/8 ge 24
> seq 10 permit 2.0.0.0/8 ge 24 le 31
>
>
>
> On Mar 22, 2009, at 6:53 , Ruhann wrote:
>
>
> the seq number is just a numerical place holder for the entries of prefix
>> list "NET".
>> you wont be able to apply both lines on the same router as the first one
>> would get a default seq-number of 5 and the second line will shout at you,
>> something like "seq already exists"
>>
>> then, x.x.x.x/x does not really equite to much in cisco land, so I cant
>> assist with the prefix difference between the two, but as for the length
>> of
>> the subnet mask, yes there is difference.
>> the first command would allow subnet lengths from /24 up to /32 (host
>> routes) and the second only up to a length of 26 bits, depending on what
>> the
>> magic /x value is.
>>
>> hth :)
>>
>>
>>
>> On Sat, Mar 21, 2009 at 9:30 PM, Raghav Bhargava <
>> raghavbhargava12@gmail.com
>>
>>> wrote:
>>>
>>
>> hi Experts,
>>> What is the difference between these 2 commands:-
>>>
>>> ip prefix-list NET permit 1.1.1.1/8 ge 24 le 32
>>>
>>> AND
>>>
>>> ip prefix-list NET seq 5 permit x.x.x.x/x ge 24 le 26
>>>
>>> What is the significance of not using the sequence number in the first
>>> Command. Also is the first command correct. I doubt it???
>>>
>>> Please advise.
>>>
>>> --
>>> Warm Regards
>>> Raghav
>>>
>>>
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>>>
>>>
>>
>> --
>> <ruhann>
>>
>>
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>
>
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>
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