DCHP is a form of BOOTP. Both are broadcast packets(as opposed to directed
to a single IP). By default, routers & gateways don't pass any broadcast
packets. But most routers support what is called BOOTP forward or in Cisco,
it's called IP helper address. WinNT also supports this. This takes the
broadcast BOOTP or DHCP request and forwards it to a manualy defined DHCP
server on another subnet. This forwarded packet is turned into a directed
packet(so it passes through routers) and includes the address of the
forwarder. This identifies the subnet for the DHCP server.
A DHCP server can serve up IP addresses for multi-IP subnets. These are
called SCOPES on DHCP servers. It will answer the request to the forwarder
and the forwarder pass the request to the orginal requester and then the
DHCP server and the requestor can talk directly.
But no there is not a seperate packet type for DHCP vs. BOOTP.
-----Original Message-----
From: Jim Harris [mailto:[EMAIL PROTECTED]]
Sent: Thursday, January 18, 2001 9:22 PM
To: [EMAIL PROTECTED]
Subject: RE: [STN] "Linux" DHCP vs "M$" DHCP???
Extreemly interesting.....
Question:
I read somewhere (here?) that one of the (posible) issues is that the
older DHCP client daemons (like in Linux), use the BOOTP protocol
instead of the DHCP protocol. (and my IT manager at work tells me that
many admins (as well as routers, gateways, switches, etc.) don't like to
pass BOOTP packets as they can be "chatty" (take up a lot of bandwidth -
give out information - etc.)
Is there a seperate broadcast packet type that is "DHCP" instead of
"BOOTP"?
Jim
Ian McDermid wrote:
> Jim,
>
> TCPDUMP puts your Ethernet Adapter in permissive mode so it captures all
> traffic passing it. You have to enable it in STN options tab selecting
> debug support and tcpdump. Make sure you have RFC 1541 compliance turned
> off (This is an Old RFC), and DHCP supplies Network Info checked in the
> external interface box.
>
> To use TCPDUMP you need to att/F8 or F9 and type in the password, Of
> Mice and Men (Caps are important). You should get a # prompt. If you
> them type tcpdump -q you will start to capture packets.
>
> DHCP works this way:
>
> A (DHCP Discover) packet is sent to the network. This is a broadcast
> packet with an IP address of 0.0.0.0 and a type of BOOTP. The host name
> is of the Parameters within the packet. Any DHCP server, or relay agent,
> listening that is within the scope of the request will respond with a
> directed packet (DHCP Offer) to the requesting MAC address. Multiple
> servers may respond. One of the offers is selected and a TCP Packet
> (DHCP Request) is sent to the DHCP Server. The DCHP server responds with
> a TCP (DHCP ACK) packet. This completes the process.
>
> What you need to look for are the replies from the DHCP server.
>
> TCPDUMP is not very easy to use or interpret. I will have a play around
> with some captures and filters
>
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