On Wed, 2010-05-05 at 22:25 -0700, Kevin Ross wrote: > On 5/5/2010 9:11 PM, Alex Samad wrote: > > On Wed, 2010-05-05 at 20:55 -0700, Kevin Ross wrote: > > > >> On 5/5/2010 6:06 PM, Miles Fidelman wrote: > >> > > [snip] > > > > > >>> - I have two network /27 network blocks that are NOT contiguous - I > >>> use one for each box > >>> > >>> > >> I'm not a networking expert, but this part seems wrong to me. I don't > >> think you're supposed to have different subnet addresses on the same > >> broadcast domain. If they both had the same subnet address, they would > >> then talk to each other over the switch and not touch the router. > >> > > Why do you think this, reason I ask is I had a rather long discussion > > with a work college about this and I am wondering were this thinking > > comes from. > > > > Which part? The part about different subnets on the same switch or > hub? If so, yes I guess there's nothing terribly wrong with doing that, > other than causing extra traffic to the router between subnets when they > could be talking directly to each other.
The question was why did he think it was bad/wrong to put to different subnets on the same broadcast domain. the extra taffic would be arp requests and broadcasts, but with all unicast packets a switch will switch ie 1 port to another port. There is no technical reason that ip subnets have to be on seperate broadcast domains - there might be security and other reasons. > > Or is it the part about the two computers talking directly to each other > without the router if they are on the same subnet? If so, I'm speaking > strictly of TCP/IP over Ethernet. Let's say you have a simple network > with a router IP address of 192.168.1.1, host A with 192.168.1.2, and > host B with 192.168.1.3. All have a subnet mask of 255.255.255.0. > > Since we are operating over Ethernet, the TCP/IP stack needs to > determine the Ethernet address to which to send a packet. If host A > wants to send a packet to a host within the subnet, for example to > 192.168.1.3, then it will first send out an ARP request to get the > Ethernet address of 192.168.1.3. When it receives it, it will then send > the packet over Ethernet to the address received via ARP, which will > cause the packet to go straight to the receiving computer, not to the > router (if using a switch not a hub). > > If the destination IP address is outside of the subnet, then it asks ARP > for the address of the router, and sends the packet over Ethernet to the > router. > > >> Another option is to change the subnet mask so that the mask then allows > >> > > careful you might loose connectivity with the router. > > > > > > I was only mentioning it as another possibility. I don't think you will > lose connectivity with the router, just with other hosts that the > computer now thinks are in the same subnet, but really need to go > through the router. But if you know that you'll never want to talk to > those hosts, then this is a viable option. well think about it, if we are talking about network 192.168.11.0/24 (for my example I will use 24 instead of 27) the server would have an address 192.168.11.55/24 (for example) and the router would have 192.168.11.1/24 if I change the netmask of the server it can no longer talk to the router because it is in a different ip network ie 192.168.11.55/22 can't talk to 192.168.11.1/24 (you can fake it on linux with iproute - see my other answer to this thread). > > > -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/1273129543.2011.6.ca...@alex-mini.samad.com.au
