DHCP svr assigning bunk IPs

[rusga]

Levi,

Consider this:

a) PC1 requests a lease. DHCP gives it.
b) PC2 requests a lease. DHCP gives it.
c) PC3 requests a lease. DHCP gives it.
d) ... and so on.

.... now, imagine that PC1, PC2, PC3... are all *the same PC* making
requests based on injected handcrafted packets. This way, the client PC
runs out the DHCP server IP address pooling.

I guess the only way to fight this is if the DHCP server checks who is
"alive" (from some of the already leased IP addresses, like FIFO) *BEFORE*
giving a new lease.

Pls, check if your DHCP server software allows this checking.

Regards,
rusga

PS: Depending on your network scenario, try setting a smaller lease time
to clients.
PSS: Some protocols are very "naive" and depend on "not so naive" software
developers.

 

[Levi]

I'm really confused on this one... I have a DHCP scope
that has approx 1000 total IPs in it. As of 2 days ago,
it had about 500 leased out, less than 50 reserved, and
400 or so available. Yesterday, I noticed that 100% of
all available IPs were leased out, and that almost all of
the 400 that were leased (that were available the day
before)were all leased at the EXACT same time. What's
really weird about this is that they all had bunk MAC
addresses (all had AT LEAST 15 chars and looked very
similar, or were very similar). ALSO, when I looked at
the scope in the IP management console, I noticed that
the leases didn't have a real "name" associated with
them... the "name" that the console used was the IP
address. I pinged the first 10 of the questionable IPs
that were leased, and got not reply. I'm curious if
having a hub connected in this subnet could cause
this... Any suggestions? Right now I'm clueless as to
what to look for... Thanks!!!