Multicast destination NAT on same network interface, with netem

Question

For testing purpose, in a big network where IT will shoot me if multicast data are not streamed in the right VLAN, I am trying to degrade multicast packets with a server running netem configuration.

In the examples below, 237.1.2.3:5000 stands for multicast destination address and port. As for now, I used it as a netem bridge this way (Current configuration):

                      ___________
                eth2 |   netem   | eth3
237.1.2.3:5000 ----->| (latency, |-----> 237.1.2.3:5000
                     |  drop...) |
                      -----------

My problem: to fit address plan, I would not be allowed to stream on output VLAN (linked to eth3) with an address reserved internally for source streams. Thus, I need to plug directly a cable to the device for which I want to provide a degraded multicast input

I was wondering how either Expected1 or Expected2 configuration could be achieved somehow, leaving the generic bridge mode away but preserving the netem stuff:

                       Expected1
                      ___________
                eth2 |   netem   | eth3
237.1.2.3:5000 ----->| (latency, |-----> 238.1.2.3:5000
                     |  drop...) |
                      -----------

                       Expected2
                      ___________
                eth2 |   netem   |
237.1.2.3:5000 ----->| (latency, |
237.1.2.4:5000 <-----|  drop...) |
                      -----------

I am pretty sure I have already done that with an old FreeBSD device before, but avoiding iptables and so on for quite a long makes me start over unfortunately... It was destination address based iptables rules if I remind properly, but I am not sure if it was multicast. If I need to filter on source address, that would not be a problem. But, if I can filter on destination address that's better since all our input streams are referenced by this field in our IP distribution list.

If it is possible,

Could you give some indication concerning the packets path inside the different spaces ?
Could you precise if you are mentioning source or destination addresses ?
Could you also please tell me if I will be able to see output packets with tcpdump directly or if I need to log onto another device of the network (regarding stack level or any other consideration since I don't remember properly the PREROUTING/POSTROUTING/... packet paths, especially in a configuration I will no do by myself).

Thanks,

--

# lsb_release -a
Description:    Debian GNU/Linux 7.2 (wheezy)

# grep -H CONFIG_IP_M /boot/config*
/boot/config-3.2.0-4-amd64:CONFIG_IP_MULTICAST=y
/boot/config-3.2.0-4-amd64:CONFIG_IP_MULTIPLE_TABLES=y
/boot/config-3.2.0-4-amd64:CONFIG_IP_MROUTE=y
/boot/config-3.2.0-4-amd64:CONFIG_IP_MROUTE_MULTIPLE_TABLES=y

# cat /proc/sys/net/ipv4/conf/*/rp_filter
0
0
0
0
0
0
0

# cat /proc/sys/net/ipv4/conf/eth*/mc_forwarding 
1
1
1
1

Multicast destination NAT on same network interface, with netem

0 Answers0