From: ccie2004 (ccie2004@excite.com)
Date: Wed Sep 14 2005 - 16:59:15 GMT-3
If your hosts are in the same broadcast domain than they should be able to communicate with each other. The problem would be when they try to connect to something on another subnet. The return traffic will never reach the hosts that are in subnet x.x.x.128. A different problem might be if your router interface is a /24 and your hosts are /25 instead of being /24. Than I don't think your hosts would be able to talk to each other and same for return traffic. Please correct me if this is incorrect. Thanks--- On Wed 09/14, Church, Chuck < cchurch@netcogov.com > wrote:
From: Church, Chuck [mailto: cchurch@netcogov.com]To: terry.francona@gmail.com, ccielab@groupstudy.comDate: Wed, 14 Sep 2005 14:26:58 -0500Subject: RE: Subnet Mask Tricks - or - I Will Show You My Mask If You Show Me Yours!The subnet mask defines what addresses are local to an interface. Ifthe network/subnet bits match the interface, it'll ARP for thedestination. If the bits are different, it's considered not on thissubnet, and the routing table is searched for the most specific match.So if you network is 172.16.1.1/25 , that means the first 25 bits mustmatch to be local to this interface. 172.16.1.0 through 172.16.1.127will all share the same first 25 bits. But at 128, the 25 bit jumps to1, and no longer matches. So you can address your hosts with 172.16.1.xand a /24 mask, but the router won't consider hosts with the last octetof 128 through 255 as local, so they'll be dead in the water...Chuck ChurchLead Design EngineerCCIE #8776, MCNE, MCSENetco Government Services -
Design & Implementation Team1210 N. Parker Rd.Greenville, SC 29609Home office: 864-335-9473Cell: 864-266-3978cchurch@netcogov.comPGP key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x4371A48D -----Original Message-----From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf OfAnthony SequeiraSent: Wednesday, September 14, 2005 1:47 PMTo: Group StudySubject: Subnet Mask Tricks - or - I Will Show You My Mask If You ShowMe Yours!I was under the false assumption that subnet masks must be identical inlength for two systems to communicate. But I do not believe this to betrue.Isn't it a fact that the addressing just has to work out so that the twosystems think they are on the same subnet?Can someone help me with the binary math that you would do to figurethisout?For example, let's say my router interface is172.16.1.1/25and I want to use /24 for all of myclients off of that interface. What isthe quickest way to calculate the usable range of addresses for
theseclient?_______________________________________________________________________Subscription information may be found at: http://www.groupstudy.com/list/CCIELab.html_______________________________________________________________________Subscription information may be found at: http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Sun Oct 02 2005 - 14:40:15 GMT-3