What in my explanation do you not understand? I assume you are familiar with binary math right?
Here we go again :-) Class D Multicast addresses go from 224.0.0.0 to 239.255.255.255 which you pointed out. The question states you need to make sure that half of these addresses are assigned a specific RP. Right. So Half of the multicast range runs from 224.0.0.0 to 231.255.255.255 right? (total of 16 /8 subnets, half of it is 8) Now we want to filter on it. I assume you are aware of the wildcard mask logic. The 2nd, 3rd and 4th octet are very simple, we just need to match anything, so our wildcard mask will look like this: 224.0.0.0 x.255.255.255 The only thing we don't know is the X. We write down 224 and 231 (first octet from the lowest and highest address). 1110 0000 = 224 1110 0111 = 231 Here we see, the last 3 bits of the octet are different and we need to match on everything that lies in between. We count up the values of those 3 bits = 1+2+4=7 So X is 7 The wildcard mask to match on HALF of the Class D multicast range is = 224.0.0.0 7.255.255.255 Is this clear for you now? For more information on how to match using a wildcard mask, check out Tyson's blogpost: http://blog.ipexpert.com/2009/06/10/wild-card-masks/ -- Regards, Rick Mur CCIE2 #21946 (R&S / Service Provider) Sr. Support Engineer – IPexpert, Inc. URL: http://www.IPexpert.com On 26 dec 2009, at 16:24, Ahmed Haji Munye wrote: > > Hi > > I still don´t understand it. I know that multicast address range is 224.0.0.0 > - 239.255.255.255 > > Regards > Ahmed > > --- Den lör 2009-12-26 skrev Rick Mur <[email protected]>: > > Från: Rick Mur <[email protected]> > Ämne: Re: [OSL | CCIE_RS] Detailed solution page 701 TASK 24.3 > Till: "Ahmed Haji Munye" <[email protected]> > Kopia: "CC IE" <[email protected]> > Datum: lördag 26 december 2009 15.05 > > Just binary math my friend :-) > > The last 3 octets are all 1, so match everything. > > First octet: > 11100000 = 224 > 00000111 = 7 > > Meaning that everything matches from 11100000 up to 11100111 > > 11100111 = 231 > > Class D addresses reach from 224 to 239, so Class D is 16 subnets large. Half > of 16 is 8 when matching 224 up to 231 you have your 8 subnets which is half > of the multicast range :-) > > > > > -- > Regards, > > Rick Mur > CCIE2 #21946 (R&S / Service Provider) > Sr. Support Engineer – IPexpert, Inc. > URL: http://www.IPexpert.com > > On 26 dec 2009, at 15:55, Ahmed Haji Munye wrote: > >> >> Hi >> >> On the detailed solution task 24.3, it says " Set R2 to advertise itself as >> as the RP for the first half of all groups" >> >> My question is from where did you get the multicast 224.0.0.0 7.255.255.255 ? >> >> Regards >> Ahmed >> >> Ta semester! - sök efter resor hos Kelkoo. >> Jämför pris på flygbiljetter och hotellrum: >> http://www.kelkoo.se/c-169901-resor-biljetter.html >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com > > > Ta semester! - sök efter resor hos Kelkoo. > Jämför pris på flygbiljetter och hotellrum: > http://www.kelkoo.se/c-169901-resor-biljetter.html
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