From: Yasser Aly (yasser.aly@noorgroup.net)
Date: Sun Jul 11 2004 - 15:01:15 GMT-3
Kenneth
Yes that makes sense :).
However, if the DHCP sub-command default-router G1 G2 can do the trick I
would vote for using it.
Is there anybody here who can help explaining how the default-router
gateway1 gateway2 command works ?
Does it provide the 1st gateway only to the clients or does it provide both
of them and it's the client responsibility to switch using the other gateway
if the 1st one fails ?
Finally is it safe to say that if you are asked to provide two gateways to
the clients such that G1 is used and preferred, where as G2 is to be used
only if G1 is not available. Can the DHCP sub-command : default-router G1 G2
would be the correct answer ??
I apologize for stressing on this but I hate to see an easy task lost just
because the usage of a wrong command.
Wait for your reply.
Yasser
-----Original Message-----
From: Kenneth Wygand [mailto:KWygand@customonline.com]
Sent: Sunday, July 11, 2004 7:44 PM
To: Yasser Aly; Dan Shechter
Cc: ccielab@groupstudy.com
Subject: RE: DHCP
Yasser,
First off, check the beginning part of the post with the "Dead Gateway
Detection" used by Microsoft clients. Again, this is a client-specific
function and not defined in RFCs.
As for your question on IRDP, it is my assumption that we are not to
consider any client-based functionality. IRDP was designed to provide a
default gateway dynamically to clients listening to these announcements, so
I would treat it as such. You could always as the proctor "if we implement
a feature where the effect of the feature is based on how the client
implements that feature, is it safe to assume that all clients will react as
per the designed feature or do we need to ensure our solution is transparent
across all client systems?" If the feature must be transparent, you can use
VRRP, GLBP or HSRP, but not IRDP or multiple default gateways.
Also, the DHCP server will not monitor the state of multiple default
gateways and will never initiate communication with the clients to which it
has active leases. The DHCP server is merely a passive box that will
maintain a database that is queried and updated based solely upon a client's
request for an IP address.
Does this make sense? :)
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 12:33 PM
To: Kenneth Wygand; 'Dan Shechter'
Cc: ccielab@groupstudy.com
Subject: RE: DHCP
Kenneth,
I checked the reference below post and it is a very interesting one.
If I am getting what is inside that post correctly solutions offered for
this task were
1) HSRP
2) IRDP
3) VRRP
4) GLBP
It is also mentioned that IRDP will need tweaking into Windows Keys for this
to work, so I wonder would IRDP be accepted as a solution from Cisco or not.
VRRP & GLBP involves defining a virtual IP to be used as the gateway in the
stations, but if you were not given an IP to configure as the virtual IP. Is
it safe that you elect one yourself ?
Also I can't find in this post if I chose to go for the DHCP sub-command
solution " default-router G1 G2 " how this will interact with hosts and if
g1 failed will the DHCP server contact hosts to alert them that G1 is not
available and they should use G2. Or hosts to check with the DHCP server
every now and then the gateways availability ?
I just dunno I can see that with each solution provided above there is a
restriction and if the question is a floating one, didn't give you a good
hint which approach to use it will be very hard to feel confident which
approach to go.
Waiting for your feedback.
Yasser
-----Original Message-----
From: Kenneth Wygand [mailto:KWygand@customonline.com]
Sent: Sunday, July 11, 2004 6:50 PM
To: Yasser Aly; Dan Shechter
Cc: ccielab@groupstudy.com
Subject: RE: DHCP
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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