The mac implementation is good for 99% of the times, since it is really fast, but the 1% of the times that it steals an ip adress it is really a pain in the ass. I don't mind to wait a few seconds to get a connection in the stardard way.
Rapid DHCP: Or, how do Macs get on the network so fast?
41–50 of 191 posts
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#42> This network recognition technique allows the Mac to very rapidly discover if it is connected to a known network. If the network is recognized (and presumably if the Mac knows that the DHCP lease is still active), it immediately and presumptuously configures its IP interface with the address it knows is good for this network. Ok, seriously? That isn't a bug in an implementation somewhere, but in fact a feature that…
Sorry, but nobody cares what the people in your room think.
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#43"This whole notion of being so proprietary in every facet of what we do has really hurt us." Steve Jobs, circa 1997
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#44> This network recognition technique allows the Mac to very rapidly discover if it is connected to a known network. If the network is recognized (and presumably if the Mac knows that the DHCP lease is still active), it immediately and presumptuously configures its IP interface with the address it knows is good for this network. Ok, seriously? That isn't a bug in an implementation somewhere, but in fact a feature that…
Sorry, but nobody cares what the people in your room think.
Wrong, I care. I don't have any way of confirming it myself so his double-checking was appreciated.
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#45Anecdotally, my mac is absolutely horrible at connecting to my wifi. I often have to try multiple times and some times I give up, have to walk over to the router and restart it before I can get on. Probably an issue with the router ultimately, but I don't have this problem with other devices.
The only time Ive ever had issues with OS X connecting to wifi was while using a cheapo router that insisted on advertising its 2.4GHz and 5GHz networks using the same SSID.
Moving to a router that allowed them to be configured with different SSIDs resolved all my issues.
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#46Congratulations! Your laptop does the equivalent of using the exit lane to jump ahead in traffic. There's bound to be an empty spot near the end, right?
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#47This implementation by the Mac feels wrong. I mean it appears to work, but it seems like a violation of the protocol and can result in problems on the network. Maybe security issues (?). I'm not an expert in any of these things, but I'd love to hear a network protocol/security experts take on this.
This certainly smells fishy, the client is relying on ARP to assume its OK to reclaim that IP address before it actually gets the authoritative answer from the DHCP server. IP networking does not require that computers submit to dhcp, so depending on how you look at it, it probably doesn't run afoul of the spec. I'd have to get a more detailed packet capture and reference some RFCs, but given DHCP isn't manditory, I…
Regarding your security statement, I didn't get that from the packet capture. The Mac is sending an ARP request for the IP addresses of the DHCP servers of networks it's been on recently. An attacker would need to know the correct MAC address to respond with -- the Mac is not sending that out in the request.
If the ARP comes back with the cached MAC address for that network, the Mac continues using the valid DHCP lease it was given. It sends a DHCP request to renew that lease, and I assume would reconfigure the interface if the request fails and discovery has to start over.
From my recollection of the DHCP RFC, if a server hands you a lease for one week, you're allowed to use that address for a week, even if you go offline for 3 days in the middle. In practice, this may not be the case.
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#48Earlier quoted context omitted.
If your DHCP server is handing out leased addresses to other clients you might have bigger problems to worry about. For example if you expect a lot of churn on the network you should be using much shorter leases times.
How is this the DHCP server's fault? DHCP is designed to reassign unused leases to new clients if the subnet is all leased out.
How can a lease be "unused" if it hasn't expired and the client that requested it never released it? Are you saying that the DHCP server pings (ICMP or ARP) each address and re-leases the ones that don't get a response?
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#49When coming out of sleep, my Macs often get a new computer name in the form of a " (N)" suffix; e.g., a Mac named "vision" will come out of sleep and mysteriously change its name (as reported in System Preferences->Sharing) to "vision (2)", then "vision (3)" after a subsequent sleep, etc.
It's annoying. I wonder if this rapid DHCP implementation has anything to do with that.
Re: Rapid DHCP: Or, how do Macs get on the network so fast?
#50It seems a little unscientific to compare logs from one machine connecting to a new networking and having to get a lease to another connecting to a network it's been on before.