Re: Trying to understand multicast packet IP routing - why src IP address affects reception ??//
Every incoming packet goes through "input routing". The result of that routing is either to receive the packet locally, drop, or forward it. There is a hidden "local" routing table, that is used to do routing for incoming packets. It is populated automatically (e.g when u add an new local interface) You can display this table and it will help you understand the behaviour of your system: ip route list table local On 04/08/2009, Lev Olshvang wrote: > > Shahar , > Thanks > > see below : > Shachar Shemesh wrote: > I'll just point out that my Multicast understanding is a bit tenuous. > > Lev Olshvang wrote: > Evening all, > > > But if I change the interface IP address to other network, these packets > are ignored at IP layer (data link layer got it since RX count is running > according to ifconfig ) > I have tcp ip forwarding set to 1 and application sets multicast socket > option to join the multicast group. > > Did you change the IP address after the socket is up? Multicast needs to > perform some handshaking before it can start sending data, and this > handshake might be done only at the "start". > > > Since this is my network driver , I reload it and set IP after reload, > as well I put some printk in it so I see data link accepts packages in > either case. tcpdump also shows these packets. > > Also, I would start the debugging by running a sniffer and seeing whether > the packets actually leave the machine, and if so, with what destination MAC > address. > >I have no problem with MAC ( driver gets the packets), I put also some > printk in net/ipv4/route.c and I see this packets are discarded at IP layer. > > Shachar > -- > Shachar Shemesh > Lingnu Open Source Consulting Ltd. > http://www.lingnu.com > > > > ___ > Linux-il mailing list > Linux-il@cs.huji.ac.il > http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il > > ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: Trying to understand multicast packet IP routing - why src IP address affects reception ??//
Shahar , Thanks see below : Shachar Shemesh wrote: I'll just point out that my Multicast understanding is a bit tenuous. Lev Olshvang wrote: Evening all, But if I change the interface IP address to other network, these packets are ignored at IP layer (data link layer got it since RX count is running according to ifconfig ) I have tcp ip forwarding set to 1 and application sets multicast socket option to join the multicast group. Did you change the IP address after the socket is up? Multicast needs to perform some handshaking before it can start sending data, and this handshake might be done only at the "start". Since this is my network driver , I reload it and set IP after reload, as well I put some printk in it so I see data link accepts packages in either case. tcpdump also shows these packets. Also, I would start the debugging by running a sniffer and seeing whether the packets actually leave the machine, and if so, with what destination MAC address. I have no problem with MAC ( driver gets the packets), I put also some printk in net/ipv4/route.c and I see this packets are discarded at IP layer. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: Trying to understand multicast packet IP routing - why src IP address affects reception ??//
I'll just point out that my Multicast understanding is a bit tenuous. Lev Olshvang wrote: Evening all, But if I change the interface IP address to other network, these packets are ignored at IP layer (data link layer got it since RX count is running according to ifconfig ) I have tcp ip forwarding set to 1 and application sets multicast socket option to join the multicast group. Did you change the IP address after the socket is up? Multicast needs to perform some handshaking before it can start sending data, and this handshake might be done only at the "start". Also, I would start the debugging by running a sniffer and seeing whether the packets actually leave the machine, and if so, with what destination MAC address. Shachar -- Shachar Shemesh Lingnu Open Source Consulting Ltd. http://www.lingnu.com ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Trying to understand multicast packet IP routing - why src IP address affects reception ??//
Evening all, I made some investigation in my Ubuntu Linux , kernel 2.6.30 Here the case : I have computer with 2 interfaces. It runs Ubuntu, kernel 2.6.30 and application that opens multicast socket and bind it to one of the interfaces, 192.168.123.1 There are only multicast packets in this net. Multicast Packets with dest address 224.45.45.45 and source address 192.168.123.23 are received by interface defined in the same network 192.168.123.0 with no problems and even delivered to application. But if I change the interface IP address to other network, these packets are ignored at IP layer (data link layer got it since RX count is running according to ifconfig ) I have tcp ip forwarding set to 1 and application sets multicast socket option to join the multicast group. I had an understanding that for multicast only destination MAC address really rules ( interface filters are set to accept specific multicast address as a result of muticats join by setsockopt() ) So the question is - why IP SRC address is taken into consideration by IP layer and how to disable this feature ?? Thank you very much .. Lev ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
