Subject: what is the meaning of "UDP Helper"?

From: "SRD Ye JianLiang" <[email-masked]>
Date: Wed, 25 Apr 2001 09:05:32 +0800

Thanks!

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From: CARDOSO Jorge Miguel <[email-masked]>
Date: Thu, 26 Apr 2001 04:14:33 +0100

Generaly 'UDP Helper' its used to name the host that process a specific
broadcast UDP packet. The word become usual because you need to configure it
on some equipment to address specific task of 'broadcast forwarding'.

-> Case study:

Imagine you have this scenario:

central-site Lan <---> Router1 <---wan---> Router2 <---> remote-site Lan

following recent design rules, you may want to keep a central DHCP server on
the central site, to be used by every remote site.

As we now, on normal condition (without 'bridjing') - broadcast packets are
not forwarded by Routers. Broadcasts are not 'routable'. The broadcast
packets are keept on broadcast domain.
With this scenario, the broadcast domain would be the remote site lan and
Bootp protocol should not work, because the broadcasts sent by the LAn-users
would not reach the DHCP server on the central site.

To solve this, you can define on the router a special Ip Address sometimes
called "UDP Helper Address"

Router2 is on client broadcast domain, so, the Lan interface receives the
client broadcasts; if you have an "UDP helper" defined, the router
transforms the destination IP Address field of broadcast packet into
something 'routable' - it can be transformed on unicast or single host.

Using this procedure, the router2 delivers the bootP packet to router1  and
finaly to the destination - the DHCP Server.

"UDP packet forwarding" is also used with some more IP protocol, rather then
BootP.

Regards,
j0rge Card0so.

-----Original Message-----
From: SRD Ye JianLiang
To: [email-masked]
Sent: 25-04-2001 2:05
Subject: what is the meaning of "UDP Helper"?

Thanks!