From: elping (elpingu@xxxxxxxxxx)
Date: Mon Aug 19 2002 - 01:44:02 GMT-3
wow...
thanks...never looked at it this way ..good thread.
Brian McGahan wrote:
> Relax guys.
>
> Regarding the subject of address class, remember that the class
> of an address has nothing to do with the subnet mask. The first four
> most significant bits determine the class of an address. As I stated
> before, these values are:
>
> Class A: 0xxxxxxx
> Class B: 10xxxxxx
> Class C: 110xxxxx
> Class D: 1110xxxx
> Class E: 1111xxxx
>
> Suppose we have three address prefixes:
>
> 10.0.0.0/8
> 16.0.0.0/4
> 31.0.0.0/31
>
> Regardless of their subnet mask, in binary terms these prefixes
> are all Class A networks. Although one is an aggregate, one is a
> "classful" network, and one is a subnet, they are all Class A addresses.
>
> Now depending on what you're asking, you can come up with
> different interpretations. If you are asking "match *all* class B
> addresses", the syntax would be:
>
> Ip prefix-list ALL_CLASS_B permit 128.0.0.0/2 le 32
>
> This syntax is saying:
> Check the first 2 bits of the prefix 128.0.0.0
> The mask must be less than or equal to 32 (everything)
>
> Therefore, this is matching all prefixes for which the most
> significant bits are 10, and are therefore class B.
>
> Now, if you're asking to match class B addresses with classful
> masks (255.255.0.0), without matching any aggregates or subnets, your
> syntax would be:
>
> Ip prefix-list CLASS_B_ONLY_CLASSFUL_MASK permit 128.0.0.0/2 ge 16 le 16
>
> This syntax is saying:
> Check the first 2 bits of the prefix 128.0.0.0
> The mask must be greater than or equal to 16
> The mask must also be less than or equal to 16 (exactly
> 16)
>
> As for reference sources on this topic, I can't help you. It's
> just binary logic.
>
> HTH
>
> Brian McGahan, CCIE #8593
> Director of Design and Implementation
> brian@cyscoexpert.com
>
> CyscoExpert Corporation
> Internetwork Consulting & Training
> http://www.cyscoexpert.com
> Voice: 847.674.3392
> Fax: 847.674.2625
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Graham, John
> > Sent: Friday, August 16, 2002 5:08 AM
> > To: 'Khalid Siddiq'; EbonyGuru@aol.com; brian@cyscoexpert.com;
> > chaimgev@hotmail.com; ciscojunkie@teamhealth.com;
> ccielab@groupstudy.com
> > Subject: RE: IP PREFIX-LIST HELP!
> >
> > I think you'll find it was a joke.
> >
> > A concept called humour.
> >
> > -----Original Message-----
> > From: Khalid Siddiq [mailto:khalid@sys.net.pk]
> > Sent: 16 August 2002 11:03
> > To: EbonyGuru@aol.com; brian@cyscoexpert.com; chaimgev@hotmail.com;
> > ciscojunkie@teamhealth.com; ccielab@groupstudy.com
> > Subject: RE: IP PREFIX-LIST HELP!
> >
> >
> > Dear all,
> > please don,t use these types of hard words,its look like some kind of
> > professional jealousy.
> > i have tested this prefix-list in my lab and its working fine.
> >
> >
> > Class A : ip prefix-list k seq 5 permit 0.0.0.0/1 ge 8 le 8
> > Class B : ip prefix-list k seq 10 permit 128.0.0.0/2 ge 16 le 16
> > Class C : ip prefix-list k seq 15 permit 192.0.0.0/3 ge 24 le 24
> >
> >
> > Please correct if i miss something.
> > regards,
> > khalid
> > -----Original Message-----
> > From: EbonyGuru@aol.com [mailto:EbonyGuru@aol.com]
> > Sent: Friday, August 16, 2002 4:29 AM
> > To: brian@cyscoexpert.com; chaimgev@hotmail.com;
> > ciscojunkie@teamhealth.com; ccielab@groupstudy.com
> > Subject: Re: IP PREFIX-LIST HELP!
> >
> >
> > Hey Brian,
> >
> > Surely you know it is dangerous to play mental games with someone that
> has
> > been sucked into the mental vortex thatis called 2 days before your
> lab.
> >
> > So, thanks for your help but you must finish what you started.
> >
> > I believe what you meant to type was the following:
> >
> > Ip prefix-list CLASS_A permit 0.0.0.0/0 ge 0 le 8
> >
> > and not:
> >
> > Ip prefix-list CLASS_A permit 0.0.0.0/1 ge 8 le 8 --- please comment
> on
> > my
> > correction.
> >
> > You have been a great help so far so now please do one of two things,
> > finish
> >
> > all the classes or refer me to a reliable reference.
> >
> > So you dont think I am lazy, this is my revised idea of class B
> filter:
> >
> > ip prefix-list CLASS_B permit 128.0.0.0/8 ge 8 le 16 ....and so on.
> >
> > Class C:
> >
> > ip prefix-list CLASS_B permit 192.0.0.0/16 ge 16 le 24
> >
> > correct, or way off?
> >
> > Now bro, end this and quit playing---- :-)
> >
> > TIA,
> >
> > E'Guru
> >
> >
> > In a message dated 15/08/2002 14:39:06 GMT Daylight Time,
> > brian@cyscoexpert.com writes:
> >
> >
> > > Subj:RE: IP PREFIX-LIST HELP!
> > >
> > >
> > > Unfortunately no one has gotten it right in this thread yet. If
> > > you write out the classes in binary, you can see that all class A
> > > addresses start with a 0 (most significant bit), all class B with
> 10,
> > > class C, 110, class D 1110, class E 1111. It's the first 4 most
> > > significant bits that determine the class of an address.
> > >
> > > To match on classful networks, we not only have to match on the
> > > prefix, but also the prefix-length. Therefore, to accept only
> classful
> > > networks, all class A's would have to have a mask of 8, B 16, C 24,
> etc.
> > > This can be accomplished with either a prefix-list or an extended
> > > access-list. Suppose we are matching class A addresses. The first
> bit
> > > must be 0, and the mask must be 8.
> > >
> > > Ip prefix-list CLASS_A permit 0.0.0.0/1 ge 8 le 8
> > > access-list 100 permit 0.0.0.0 127.0.0.0 host 255.0.0.0
> > >
> > > The prefix-list syntax reads:
> > >
> > > Check against the first bit of 0.0.0.0
> > > The mask is greater than or equal to 8
> > > The mask is also less than or equal to 8 (exactly 8)
> > >
> > > Access-list syntax reads basically the same.
> > >
> > > Check the first bit, it must be 0
> > > The mask is exactly 8
> > >
> > > I don't want to spoil all the fun, so let's see if you guys can come
> up
> > > with the syntax for class B and class C.
> > >
> > > HTH
> > >
> > > Brian McGahan, CCIE #8593
> > > Director of Design and Implementation
> > > brian@cyscoexpert.com
> > >
> > > CyscoExpert Corporation
> > > Internetwork Consulting & Training
> > > http://www.cyscoexpert.com
> > > Voice: 847.674.3392
> > > Fax: 847.674.2625
> > >
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > > Chaim Gev
> > > Sent: Thursday, August 15, 2002 7:51 AM
> > > To: ciscojunkie@teamhealth.com; EbonyGuru@aol.com;
> > > ccielab@groupstudy.com
> > > Subject: Re: IP PREFIX-LIST HELP!
> > >
> > > and what about subnets of the callas B networks?
> > >
> > >
> > > >From: "CiscoJunkie" <ciscojunkie@teamhealth.com>
> > > >Reply-To: "CiscoJunkie" <ciscojunkie@teamhealth.com>
> > > >To: <EbonyGuru@aol.com>, <ccielab@groupstudy.com>
> > > >Subject: Re: IP PREFIX-LIST HELP!
> > > >Date: Thu, 15 Aug 2002 07:59:47 -0400
> > > >
> > > >I hate to sound TOO logical, but if you are asked to "filter all
> class
> > > B
> > > >nets" (allow in our deny them in??), would it not simply just be:
> > > >
> > > >"ip refix-list zib seq 10 (permit or deny) 0.0.0.0/16"
> > > >
> > > >----- Original Message -----
> > > >From: <EbonyGuru@aol.com>
> > > >To: <ccielab@groupstudy.com>
> > > >Sent: Thursday, August 15, 2002 4:57 AM
> > > >Subject: IP PREFIX-LIST HELP!
> > > >
> > > >
> > > > > Hey Guys,
> > > > >
> > > > > Can someone please help me check if this is correct:
> > > > >
> > > > >
> > > > > To filter all class B nets:
> > > > >
> > > > > ip prefix-lis zib seq 10 permit 0.0.0.0/0 ge 16 le 24
> > > > >
> > > > > Please also tell me where to find a reference with configuration
> > > >examples.
> > > > >
> > > > > TIA.
> > > > >
> > > > > E'Guru
> > > > >
This archive was generated by hypermail 2.1.4 : Sat Sep 07 2002 - 19:48:30 GMT-3