|
Home > Archive > alt.certification.mcse > September 2002 > DHCP Question
You are viewing an archived Text-only version of the thread.
To view this thread in it's original format and/or if you want to reply to
this thread please [click here]
|
|
| OrangeC@ 2002-09-25, 8:29 am |
| I'm awaiting a date for exams 216 & 217. This isn't regarding the exams, but
it has puzzled me for ages.
Lets say there is a supernetted network, 2 DHCP severs one for each subnet
or 2 subnets connected by a RFC1542 Router, again 2 DHCP servers. How does a
DHCP server know which subnet a client is on, when all clients broadcast
their MAC addresses and same destination 255.255.255.255 & source 0.0.0.0
IP's? Client accepts first offer it gets, what if its from the 'wrong' DHCP
server. (Hope that clear?)
I guess if a DHCP relay agent is used the correct IP will be given coz the
relay agent directs the 'discover' to an actual DHCP server.
OrangeC@
To Reply take out 'my_willy'
| |
| 70-228 2002-09-25, 8:29 am |
| "OrangeC@" <orangecat02'my_willy'@clara.co.uk> wrote in message
> I'm awaiting a date for exams 216 & 217. This isn't regarding the exams,
but
> it has puzzled me for ages.
>
> Lets say there is a supernetted network, 2 DHCP severs one for each subnet
> or 2 subnets connected by a RFC1542 Router, again 2 DHCP servers. How does
a
> DHCP server know which subnet a client is on, when all clients broadcast
> their MAC addresses and same destination 255.255.255.255 & source 0.0.0.0
> IP's? Client accepts first offer it gets, what if its from the 'wrong'
DHCP
> server. (Hope that clear?)
Set up net monitor and filter for DHCP packets and have a good look at the
contents of those packets. I could just tell you the answer but you'll learn
a heck of a lot more if you do this...
| |
| OrangeC@ 2002-09-25, 2:29 pm |
| Thanks, will do. I agree and am glad u told me this way 
OrangeC@
"70-228" <ToldePD@ariz.ka> wrote in message
news:svik9.5030$8H6.41518@news.easynews.com...
> "OrangeC@" <orangecat02'my_willy'@clara.co.uk> wrote in message
> > I'm awaiting a date for exams 216 & 217. This isn't regarding the exams,
> but
> > it has puzzled me for ages.
> >
> > Lets say there is a supernetted network, 2 DHCP severs one for each
subnet
> > or 2 subnets connected by a RFC1542 Router, again 2 DHCP servers. How
does
> a
> > DHCP server know which subnet a client is on, when all clients broadcast
> > their MAC addresses and same destination 255.255.255.255 & source
0.0.0.0
> > IP's? Client accepts first offer it gets, what if its from the 'wrong'
> DHCP
> > server. (Hope that clear?)
>
> Set up net monitor and filter for DHCP packets and have a good look at the
> contents of those packets. I could just tell you the answer but you'll
learn
> a heck of a lot more if you do this...
>
>
| |
| OrangeC@ 2002-09-25, 3:29 pm |
| Thanks, will do. I agree and am glad u told me this way
OrangeC@
"70-228" <ToldePD@ariz.ka> wrote in message
news:svik9.5030$8H6.41518@news.easynews.com...
> "OrangeC@" <orangecat02'my_willy'@clara.co.uk> wrote in message
> > I'm awaiting a date for exams 216 & 217. This isn't regarding the exams,
> but
> > it has puzzled me for ages.
> >
> > Lets say there is a supernetted network, 2 DHCP severs one for each
subnet
> > or 2 subnets connected by a RFC1542 Router, again 2 DHCP servers. How
does
> a
> > DHCP server know which subnet a client is on, when all clients broadcast
> > their MAC addresses and same destination 255.255.255.255 & source
0.0.0.0
> > IP's? Client accepts first offer it gets, what if its from the 'wrong'
> DHCP
> > server. (Hope that clear?)
>
> Set up net monitor and filter for DHCP packets and have a good look at the
> contents of those packets. I could just tell you the answer but you'll
learn
> a heck of a lot more if you do this...
>
>
| |
|
|
"OrangeC@" <orangecat02'my_willy'@clara.co.uk> wrote in message
news:1032957647.40649.0@demeter.uk.clara.net...
> I'm awaiting a date for exams 216 & 217. This isn't regarding the exams,
but
> it has puzzled me for ages.
>
> Lets say there is a supernetted network, 2 DHCP severs one for each subnet
> or 2 subnets connected by a RFC1542 Router, again 2 DHCP servers. How does
a
> DHCP server know which subnet a client is on, when all clients broadcast
> their MAC addresses and same destination 255.255.255.255 & source 0.0.0.0
> IP's? Client accepts first offer it gets, what if its from the 'wrong'
DHCP
> server. (Hope that clear?)
>
> I guess if a DHCP relay agent is used the correct IP will be given coz the
> relay agent directs the 'discover' to an actual DHCP server.
>
>
>
From Q120932
SUMMARY
A DHCP (Dynamic Host Configuration Protocol) server can provide IP addresses
to clients spanning multiple subnets if the router that separates them can
act as an rfc 1542(BOOTP) relay agent. If the router cannot function as
relay agent, each subnet that has DHCP clients requires a DHCP server.
MORE INFORMATION
A relay agent that conforms to rfc 1542 relays DHCP packets to the remote
side even though they are broadcast packets. Before relaying a DHCP message
from a DHCP client, the agent examines the GIADDR (gateway IP address)
field. If the field has an IP address of 0.0.0.0, the agent fills it with
the router's IP address. When the DHCP server receives the message, it
examines the Relay IP Address field to see if it has a DHCP scope (a pool of
IP addresses) that can be used to supply an IP address lease. If the DHCP
server has multiple DHCP scopes, the address in the Relay IP Address field
identifies the DHCP scope from which to offer an IP address lease. This
process allows one DHCP server to manage different scopes for subnets.
Jerry
| |
|
|
"OrangeC@" <orangecat02'my_willy'@clara.co.uk> wrote in message
news:1032957647.40649.0@demeter.uk.clara.net...
> I'm awaiting a date for exams 216 & 217. This isn't regarding the exams,
but
> it has puzzled me for ages.
>
> Lets say there is a supernetted network, 2 DHCP severs one for each subnet
> or 2 subnets connected by a RFC1542 Router, again 2 DHCP servers. How does
a
> DHCP server know which subnet a client is on, when all clients broadcast
> their MAC addresses and same destination 255.255.255.255 & source 0.0.0.0
> IP's? Client accepts first offer it gets, what if its from the 'wrong'
DHCP
> server. (Hope that clear?)
>
> I guess if a DHCP relay agent is used the correct IP will be given coz the
> relay agent directs the 'discover' to an actual DHCP server.
>
>
>
From Q120932
SUMMARY
A DHCP (Dynamic Host Configuration Protocol) server can provide IP addresses
to clients spanning multiple subnets if the router that separates them can
act as an rfc 1542(BOOTP) relay agent. If the router cannot function as
relay agent, each subnet that has DHCP clients requires a DHCP server.
MORE INFORMATION
A relay agent that conforms to rfc 1542 relays DHCP packets to the remote
side even though they are broadcast packets. Before relaying a DHCP message
from a DHCP client, the agent examines the GIADDR (gateway IP address)
field. If the field has an IP address of 0.0.0.0, the agent fills it with
the router's IP address. When the DHCP server receives the message, it
examines the Relay IP Address field to see if it has a DHCP scope (a pool of
IP addresses) that can be used to supply an IP address lease. If the DHCP
server has multiple DHCP scopes, the address in the Relay IP Address field
identifies the DHCP scope from which to offer an IP address lease. This
process allows one DHCP server to manage different scopes for subnets.
Jerry
|
|
|
|
|