From: ccie candidate (ccie1@xxxxxxxxx)
Date: Fri Aug 16 2002 - 14:51:53 GMT-3
Brain ;
you are absolutely right ..i have a post like 3 days ago solve the same problem
with access-list .none comment on it ...all it needs is to make sure that the
first two bits are 10 .
--On Fri, 16 Aug 2002 11:30:55 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 >> > > >
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