Arp errors in /var/log/messages!  

kernel: arplookup 10.1.1.1 failed: host is not on local network
I noticed a BUNCH of these errors in the /var/log/messages file. What I was doing: I have a network, let's call it 10.1.1.0/24, and I want to split that /24 into /26 networks. The goal is to plug the networks into their own ports on the router or to utilize VLANS on the switches. So, I switched a box on 10.1.1.100 from a netmask of 255.255.255.0 (/24) to 255.255.255.192 (/26). The machines netblock is not 10.1.1.64/26. Immediately, arp started complaining and logging to /var/log/messages. The messages are all "I hear an ARP from some IP out of my netblock and I don't know what to do". A stop gap measure to stop the error logs is to configure a static route to the /24 (bascially, you tell the ethernet to not use the gateway to contact the /24, but to just send out traffic destined for the /24 out of the IP on the /26. This stops the kernel: arplookup 10.1.1.1 failed: host is not on local network errors! Here is the command: route add -net 10.1.1.1/24 10.1.1.100 -interface [man route]
Is this the correct way to do things? Probably not! I should wait until I plug them into the other router port and then muck with the netmasks. As it stands, if I plop them in another port, I'll need to drop the static route, and then make sure the other machines in the /24 all get switched to a /26 at the same time or else the machines in the /24 will not be able to connect to the ones in the /26. The lesson: plan ahead when numbering your machines. If you have a /24 with 4 customers, you probably want to split up the /24 into smaller netblocks and give them /26 netmasks. Once you start doing a bunch of bandwidth, VLANs and multiple routers will be needed.