From: Kenneth Wygand (KWygand@customonline.com)
Date: Sun Jul 11 2004 - 12:50:02 GMT-3
Yasser,
I recently discussed this in a detailed thread about a week or two ago.
Please check out the following link from the archives. Read the whole
thread from the bottom up, and let me know if you have any additional
questions! :)
http://www.groupstudy.com/archives/ccielab/200407/msg00299.html
Kenneth E. Wygand
Systems Engineer, Project Services
CISSP #37102, CCNP, CCDP, ACSP, Cisco IPT Design Specialist, MCP, CNA,
Network+, A+
Custom Computer Specialists, Inc.
"The only unattainable goal is the one not attempted."
-Anonymous
-----Original Message-----
From: Yasser Aly [mailto:yasser.aly@noorgroup.net]
Sent: Sunday, July 11, 2004 11:39 AM
To: Kenneth Wygand; 'Dan Shechter'
Cc: ccielab@groupstudy.com
Subject: RE: DHCP
Hi Kenneth,
Taking advantage of discussing DHCP topic and I would like to add
another
question.
Suppose that you are asked to provide 2 Gateways to the hosts where as
let's
say gateway G1 should be preferred over gateway G2 and G2 to be used
only if
G1 is not available. HSRP is not an option.
I thought that this can be achieved in two ways
1) Using the DHCP sub-command: default-router G1 G2
2) Using IRDP
I wonder technically which one of these solutions would be more correct.
If I used solution one how it will work ? Will the host re-contact the
DHCP
server to get his second gateway or the router
Will always provide G1 as the gateway and will never provide G2 to the
hosts.
I want to know how and when G2 will be provided to the hosts using
Solution
1
Same questions are directed to solution 2.
Thanks,
Yasser
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Kenneth Wygand
Sent: Sunday, July 11, 2004 6:22 PM
To: Dan Shechter
Cc: ccielab@groupstudy.com
Subject: RE: DHCP
Dan,
No, the IOS will not give those out so you do not need to exclude them.
However, make sure you exclude the following addresses (if they are
within
the network range you are adding to your DHCP scope):
1) Any addresses specifically said to exclude or "not assign"
2) Default Gateway (default network) (this will always be within your
network range).
3) DNS (if it's in the range of the DHCP pool)
4) WINS (if it's in the range of the DHCP pool)
Also notice one other important "gotcha":
If you need to enter, say, 2 DNS entries into your DHCP pool, *MAKE SURE
YOU
PUT THEM ON THE SAME LINE*. If you put them as two separate lines, your
second command will actually *REPLACE* the first command and you will
lose
your first DNS server (or WINS, or DEFAULT NETWORK, or whatever).
Keep all the points you can get... :)
Kenneth E. Wygand
Systems Engineer, Project Services
CISSP #37102, CCNP, CCDP, ACSP, Cisco IPT Design Specialist, MCP, CNA,
Network+, A+
Custom Computer Specialists, Inc.
"The only unattainable goal is the one not attempted."
-Anonymous
-----Original Message-----
From: Dan Shechter [mailto:danshtr@yahoo.com]
Sent: Sunday, July 11, 2004 5:13 AM
To: Kenneth Wygand
Subject: Re: DHCP
Kenneth,
So when using ip dhcp exculde we have to exclude also all 0 and all 1 ?
Kenneth Wygand wrote:
>Tim,
>
>Yes, DHCP is "smart enough" not to distribute those host addresses.
>Here is the logic:
>
>When you configure a pool of addresses in the DHCP pool, you give it
the
>network number (0's in host portion) and the prefix length (or
>equivalent subnet mask). The DHCP service knows not to give out the
all
>0's or all 1's address for the host portion. If the DHCP valid
>addresses were entered into the IOS like the excluded addresses
>(starting IP address and ending IP address), then DHCP might not be "so
>smart".
>
>It should be noted, however, that IP addresses you list in the various
>DHCP options (Default Network/Gateway, DNS, WINS, etc), all *MUST* be
>excluded from the range if they fall in the network portion you
>configured (obviously the default network/gateway must be in this local
>address range).
>
>Also, according to Scott Morris (I haven't tested this, so I use this
>disclaimer :) [Hi Scott!]), if you configure manual bindings in
>alternate DHCP pools, but the manual binding is part of the dynamic
>range in your first pool, the IOS actually creates a binding for that
>manually-bound address so it won't attempt to give out that IP address
>in the dynamic range. As a result, you don't need to exclude manual
>bindings from the dynamic range.
>
>This does make sense since once the network ranges or host "range" is
>configured, the "excluded-addresses" are defined globally on the
router,
>not within a specific range.
>
>HTH!
>
>Kenneth E. Wygand
>Systems Engineer, Project Services
>CISSP #37102, CCNP, CCDP, ACSP, Cisco IPT Design Specialist, MCP, CNA,
>Network+, A+
>Custom Computer Specialists, Inc.
>"The only unattainable goal is the one not attempted."
>-Anonymous
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>ccie2be
>Sent: Friday, July 09, 2004 7:04 AM
>To: Group Study
>Subject: DHCP
>
>Hi guys,
>
>Is dhcp smart enough to know not to distribute invalid ip host
addresses
>such
>as 172.16.15.0/24 and 172.16.15.255/24 or do we have to manually
exclude
>these
>addresses?
>
>TIA, Tim
>
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