Subject: Re: Mrouted and multicast tools on ONE LINUX Box?

From: Richard Underwood <[email-masked]>
Date: Fri, 28 Jun 96 10:15:23 BST

At 17:39 27/06/96 +0100, D E PRICE wrote:
>Dear All,
>	Has anyone run MROUTED and MBONE applications tools
>on just one LINUX box simultaneously?
>
        Which version of the Linux kernel are you using?

                Richard

---

From: D E PRICE <[email-masked]>
Date: Fri, 28 Jun 1996 11:47:47 +0100

Dear Richard and Friends,
	I asked about linux / mrouted / application problems....

	Richard asked `which version'
reply:
	It claims to be LINUX 2.0.0 and I think
(i.e. someone lese loaded it) that it arrived from red Hat.

Further info....

When I have 224.0.0.0 routed onto the empty ethernet, I get
the following when I run a mtrace....
=============================
 ./mtrace 206.167.193.10 224.0.0.1
Mtrace from 206.167.193.10 to 193.60.14.97 via group 224.0.0.1
Querying full reverse path... IP data field too short (4 bytes) for IGMP from 193.60.14.97
* switching to hop-by-hop:
  0  spider-ether.dcs.aber.ac.uk (193.60.14.97)
 -1  IP data field too short (4 bytes) for IGMP from 193.60.14.97
* IP data field too short (4 bytes) for IGMP from 193.60.14.97
* IP data field too short (4 bytes) for IGMP from 193.60.14.97
* Timed out receiving responses
Perhaps no local router has a route for source 206.167.193.10
==================

Why am I getting all the `` IP data field too short (4 bytes) for IGMP from 193.60.14.97''
complaints?

Dave Price

---

From: Malcolm Beattie <[email-masked]>
Date: Fri, 28 Jun 1996 14:43:55 +0100 (BST)

> the following when I run a mtrace....

I'm getting this too while trying to set up mrouted 3.81 on Linux 2.0.
I've reported it to Alan Cox already (along with a "kernel Aiee"
triggered by mrouted). Now that the Linux 2.0 headers are the standard
ones, there are only two slight differences in the way Linux does
mrouted: it talks down a raw IGMP socket to control IGMP (instead of
down a UDP socket) and ip->ip_len is, as in the raw IP packet, a
network short which includes iphdrlen. I've been doing more digging.

After creating its control socket and making sure it loops back with
setsockopt IP_MULTICAST_LOOP, strace shows the following:

sendto(3, "E\0,\0\0\0\0\0\377\2\0\0\243\1\2\16\340\0\0\2\37 \7\'\340\2\0\1\243\1 \217\243\1\2\16\243\1\2\16v\5u\377", 44, 0, {sin_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("224.0.0.2")}, 16) = 44
setsockopt(3, IPPROTO_IP34, [-414720], 1) = 0
recvfrom(3, "E\0\0\34\306\353\0\0\1\2l\305\243\1\2\16\340\0\1 \26\0\10\337\340\0\1 ", 8192, 0, NULL, 0xbffffa30) = 28
recvfrom(3, "E\0\0\30\306\357\0\0\377\2o\342\243\1\2\16\340\0\0\2\37 \7\'", 8192, 0, NULL, 0xbffffa30) = 24
IP data field too short (4 bytes) for IGMP from 163.1.2.14

The 44 bytes sent are an IGMP_MTRACE packet, the first packet of 28
bytes received is an IGMP_HOST_NEW_MEMBERSHIP_REPORT (according to
the igmphdr type field) and the next 24 byte packet is the looped
back IGMP_MTRACE packet--truncated. It looks as though the kernel
(perhaps only when looping back) is truncating it by 20 bytes which
just happens to be the IP header size. I'm cc'ing this to Alan in the
hope that there's a one-line packet-length fix to make somewhere which
will cure all this. I can't even run a tunnel between two Linux boxes.

--Malcolm

-- 
Malcolm Beattie <[email-masked]>
Unix Systems Programmer
Oxford University Computing Services

---

From: Colin Perkins <[email-masked]>
Date: Fri, 28 Jun 1996 12:05:07 +0100

>(i.e. someone lese loaded it) that it arrived from red Hat.

It's RedHat 3.0.3, upgraded to kernel 2.0.0 (I'm the one who loaded it...)

Colin

---

From: D E PRICE <[email-masked]>
Date: Fri, 28 Jun 1996 17:42:44 +0100

Dear Malcolm,
	Thanks for the email. At least I have one LINUX to SunOS 4.1.3+m3.5/8
tunnel working...... ( i think)....

Please keep me informed if you here more / learn more
and I will do similarly....

Dave Price

---

From: [email-masked] (Alan Cox)
Date: Fri, 28 Jun 1996 18:14:06 +0100 (BST)

> will cure all this. I can't even run a tunnel between two Linux boxes.

I hope its a one liner. I can now simulate what you are seeing which is the
first stage. I should also be getting a couple more ethernet cards so I can
build a two networks with tunnel setup to debug this.

More when I have something fixed.

Alan