dhcp fails with big dhcpd.leases
dhcp1 at thehobsons.co.uk
Thu Sep 2 07:00:39 UTC 2010
Thinking some more about this, I'll add a few thoughts on things that
have popped up.
1) Big bridged network.
I'd personally doubt the sense in having one huge bridged network. If
the number of active clients grows as big as dorian suggests, then I
could see the amount of broadcast traffic getting quite significant.
Unless all the links in the network are fairly high in capacity, I
could see a situation where a big chunk of network capacity is taken
up with broadcast traffic.
It potentially makes any troubleshooting harder, since it won't be
quick and easy to identify the location of a device causing problems
- that would involve looking into the traffic and querying switches
etc to find the device (although he may have put systems in place to
2) Does anyone know if there are any problems running dhcpd on a
bridge interface ?
3) dorian also suggests they want to keep client IPs the same and
this is important for management purposes. Two problems with this :
Unless he uses fixed addresses or reserved leases, then a clients
address is not guaranteed. All it takes is just one bad (or
malicious) device, and some or all devices with expired leases could
find their addresses change when they next connect.
Secondly, any device can change it's address quite easily - just by
changing client-id (trivial) or MAC address (almost trivial these
Relying on IP addresses not changing is likely to come back at some
point and bite - badly. It also means that the evidence is unreliable
should it be used for legal purposes. There has already been at least
one well publicised case where an innocent victim was dragged into
court on copyright theft charges because the ISP got their timezone
wrong and gave the wrong customer details relating to the IP in
If you need to keep track of who is using the network and when and
what they are doing (such as billing for traffic) then some other
mechanism needs to be in place - neither IP nor MAC address are
adequate for this.
3b) Giving customers the appearance of fixed addresses will raise
expectations. Some customers will get accustomed to it, and will get
upset if their IP does change. Having fewer IPs than customers (but
enough to satisfy all concurrent needs) and forcing some churn will
keep expectations realistic.
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