Re: Strange VLAN / DHCP / IP issue...
- From: "Omar" <holografique@xxxxxxxxx>
- Date: 15 Nov 2006 15:54:50 -0800
1. There is no router needed because the VLAN's exist on the Catalyst
4506 distribution switch, which is layer three and handles the routing
between VLAN's internally. no router needed.
2. I believe I figured out what the issue is:
one thing I did not indicate is that the USER scopes are under a single
SuperScope on the DHCP Server. I thought Superscopes were just a simple
way to organize your scopes.
Apparently not.
By definition (from Microsoft) a Superscope is used for multi-neting,
and essentially tells the DHCP server that all scopes within the
Superscope are part of the same "physical segment". Thus what I think
is happening is that the DHCP server is ignoring the fact that the new
client DHCP request is coming from a different VLAN/subnet. Since it's
being told that all the Scopes exist on the same physical segment, he
is essentially ignoring the "giaddr" or "source address" from the
source VLAN that the client DHCP request is coming from, thus
essentially allowing the client to receive his old address even though
the request clearly came from a different VLAN.
I removed the superscope and doing some testing today to see if it's
fixed.
cheers!
-omar
Phillip Windell wrote:
"Omar" <holografique@xxxxxxxxx> wrote in message
news:1163550625.651862.76940@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
How is the Laptop able to get an IP address from a VLAN that is he is
not physically/logically connected? He is connected to VLAN 102
(10.199.29.0 / 24) but get's his old IP address from VLAN 101
(10.199.28.0 / 24). WTF?
1. Setup looks great, but where is the LAN Router to route between the
segments? Giving us brand and model numbers doesn't help,...I haven't
memorized everyones products and what each model can do :-)
2. Just a guess, but, your Switch ports may be statically set to a certain
VLAN, but dynamically (frame tagging) able to exist on any subnet,...so the
laptop even though moved to a new switch port is still technically on the
same segment as before because the switch port is capable of "servicing"
multiple segments (1 static, but multiple dymanically [tagging]). This can
"confuse" the DHCP server so that it does not understand what segment the
"query" actually came from,...and since DHCP Clients always request the same
IP Config they had last time,...whala,...it gets the same Config instead of
being denied and being forced to get a new Config.
--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
The views expressed are my own (as annoying as they are), and not those of
my employer or anyone else associated with me.
-----------------------------------------------------
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