From: naveen M S (navin.ms@gmail.com)
Date: Fri Mar 27 2009 - 20:39:23 ART
And yes, the sequence numbers are added by IOS.
On Fri, Mar 27, 2009 at 4:37 PM, naveen M S <navin.ms@gmail.com> wrote:
> 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 by IOS.
>
>
> 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
>>>>
>>>>
>>>> Blogs and organic groups at http://www.ccie.net
>>>>
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>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>> --
>>> <ruhann>
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
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>>
>>
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>>
>> _______________________________________________________________________
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