From: P729 (p729@xxxxxxx)
Date: Mon Jul 15 2002 - 02:28:28 GMT-3
Careful, 'ip directed-broadcast' is an interface-level command that allows
the conversion of a directed-broadcast into a full-on layer-3 and layer-2
broadcast. For example, a directed-broadcast to the 192.168.1.0/24 subnet
would start off being addressed to 192.168.1.255. When it reaches the
interface with 'ip directed-broadcast' enabled, the router converts the
destination IP address to the all networks address (all ones or
255.255.255.255) and the destination MAC address to all ones as well. As you
can imagine, it can be an effective DoS tool if abused.
'ip forward-protocol' is a global-level command that works hand-in-hand with
'ip helper-address' (and UDP flooding) to fine tune which UDP broadcasts are
relayed as unicasts by the 'ip helper-address' command.
Regards,
Mas Kato
https://ecardfile.com/id/mkato
----- Original Message -----
From: "Tony Huang" <thuang@tdwaterhouse.com.au>
To: "'Michael Jia'" <mjia@cisco.com>
Cc: <ccielab@groupstudy.com>
Sent: Sunday, July 14, 2002 6:34 PM
Subject: RE: ip directed broadcast, ip forward protocol
> Michael,
> Some of the links below might be of help:
> http://www.cisco.com/warp/public/707/21.html#directed-bcast
>
http://www.cisco.com/univercd/cc/td/doc/product/atm/c8540/12_0/13_19/cmd_ref
> /i.htm#xtocid12
>
> Basically ip directed-broadcast is used forward broadcast as unicast to
its
> destionation in case that ip helper-address is employed to forward
> broadcast, ip forward protocol is to define what kind of protocol will be
> forwarded instead of the default protocols:
> Trivial File Transfer Protocol (TFTP) (port 69)
> Domain Naming System (port 53)
> Time service (port 37)
> NetBIOS Name Server (port 137)
> NetBIOS Datagram Server (port 138)
> Boot Protocol (BOOTP) client and server datagrams (ports 67 and 68)
> TACACS service (port 49)
> IEN-116 Name Service (port 42)
> You may also want to use no ip forward-protocol to modify default
protocols.
>
> Hope it helps,
>
> Tony
>
> -----Original Message-----
> From: Michael Jia [mailto:mjia@cisco.com]
> Sent: Monday, 15 July 2002 10:31 AM
> To: Ccielab@Groupstudy. Com
> Subject: ip directed broadcast, ip forward protocol
>
>
> Hi, group
>
> Could someone please explain what is these commands doing?
> I have a hard time understand the Cisco Doc.
>
> An example would be great, too.
>
> Thanks
>
> --
> Michael Jia
> =
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