Subject: Re: Soved problem receiving udp broadcasts

From: Pieter <[email-masked]>
Date: Wed, 13 Jul 2011 12:09:28 +0200

Hi

The problem was that "reverse-path filtering" was enabled. after
disabling reverse-path filtering I could receive broadcasts as
expected.

As a side note - interface does not need to be in promiscuous mode

cheers pieter

On 13/07/2011 10:03, Pieter wrote:

Hi
All

Im running Linux 2.6.32.14 on an embedded  MPC4858.

One of the Application (CLI) must reciece a UDP broadcast packet.

The problem is that I only receive packets broadcast from within
the same subnet  (192.168.0.x)  even though the broadcast app
sends the broadcast to  255.255.255.255.

when i run tcpdump on the embedded machine it shows both
broadcasts from the same subnet well as different subsets: as
shown below:

SDH-0A000221> /tmp/tcpdump port 23 or port 33334

tcpdump: verbose output suppressed, use -v or -vv for full
protocol decode

listening on eth0, link-type EN10MB (Ethernet), capture size
65535 bytes

(1)    07:48:35.787826 IP 172.16.63.184.cli >
255.255.255.255.cli: UDP, length 58

(2)   07:48:43.832539 IP 192.168.0.1.cli > 255.255.255.255.cli:
UDP, length 60

(3)    07:48:43.840627 IP 192.168.0.254.cli > 192.168.0.1.cli:
UDP, length 112

The embedded machine is configured with:

ip 192.168.0.254

mask 255.255.0.0

(1) is a broadcast from a different subnet

(2) is broadcast from within same subnet

(3) the imbeded applications reply to the broadcast from same
subnet

The service has been delared in  "etc/xinetd.d/cli" as follows:

service cli

{

socket_type        = dgram

protocol        = udp

port            = 23

wait            = yes

user            = root

server            = /usr/vastech/in.cli

disable            = no

cps                = 10 5

flags            = IPv4

}

and the port assigned in "/etc/xinetd.d/services" as follows (port
23 for back comparability with older products)

#telnet        23/udp

cli                23/udp

cli                33334/udp

Is there something basic that I have overlooked ? should the
interface be set and left in

promiscuous mode to do what I require?

thanks pieter

--
VASTech PTY (LTD)
021 880 9807