On Sun, Aug 27, 2000 at 01:04:52PM -0400 or thereabouts, Sean Wu wrote:
> Actually, that was my questions too. I am not sure if all broadcast are
> based on udp instead of TCP, like all multicast are based on udp to avoice
> unnecessary retransmission. Maybe broadcast is the same case. Is my
> understanding correct?
Broadcasts are connectionless, which classifies them as UDP.
> Cisco has a "ip forward-protocol dns", is it true that it is designed for
> diskless workstation, say the DNS server ip add is not configured and need
> broadcast dns query request? I think normally DNS ip address is already
> pre-configured, so the DNS query should be a unicast instead of broadcast.
If you have an ip helper-address defined, then essentially, the forward-protocol
is defined by default, as all broadcasts that come in that interface will be
sent to that address. This means any dhcp, tftp, dns, netbios, etc broadcasts
will be sent to the helper-address defined.
That can end up being quite an amount of traffic depending upon the size of
your network. The forward-protocol will also allow you to specify which
protocols you do not want forwarded:
no ip forward-protocol udp netbios-ns (port 137, netbios name service)
This will cut down on any unnecessary/unwanted traffic going out to the
specified helper-address.
Also, keep in mind when configuring what will be forwarded and what will
not be, that the ip helper-address is assigned to the interface, but the
forward-protocol is a global configuration command.
Hope this helps,
Erica
-------------------------------
Erica L Johansson
Network Engineer
Cablevision Systems Corporation
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