[Xen-users] Multicasting + NAT networking

[Thomas Im <thim@xxxxxxxxxxxxxx>]

Hi all,

Apologies if this is a repost.  We're having trouble with multicasting  
on our NAT'd XEN network and we'd like to know if anyone has got this  
working or point us in the right direction.
Here is our current setup:  Xen (2.6.24-16-xen) running on Ubuntu 8.04  
(hardy-heron) using the NAT networking scripts to create the network.   
Everything seems to be working as it should in a NAT network:
- Dom0 can access the external network
- Dom0 can access the DomUs
- DomUs can access the external network through Dom0
- The external network cannot access DomUs
- DomUs can access each other (ssh works)

An ifconfig on Dom0 and the DomUs indicates that multicast is up and  
running. We ran a multicast test between Dom0 and a DomU which worked  
after we explicitly added a multicast route on Dom0 between them.
However, multicasts between two (or more) DomUs does not work. Neither  
DomUs can send or receive multicasts to the other.  Our guess is that  
multicasts sent by a DomU are not being forwarded to the others.   
We've read that creating vnets may solve this problem but it is not  
well documented.  If anyone has experience with this and can give us  
some tips, it'd be much appreciated. Thanks.
Here's some info on our network:

> ifconfig on dom0:

eth0      Link encap:Ethernet  HWaddr 00:1e:4f:cf:4b:b3
        inet addr:XXX.XXX.XXX.49  Bcast:XXX.XXX.XXX.127  Mask: 
255.255.255.128
        inet6 addr: fe80::21e:4fff:fecf:4bb3/64 Scope:Link
        UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
        RX packets:297887 errors:0 dropped:0 overruns:0 frame:0
        TX packets:58715 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:1000
        RX bytes:197419483 (188.2 MB)  TX bytes:5299542 (5.0 MB)
        Interrupt:19

lo        Link encap:Local Loopback
        inet addr:127.0.0.1  Mask:255.0.0.0
        inet6 addr: ::1/128 Scope:Host
        UP LOOPBACK RUNNING  MTU:16436  Metric:1
        RX packets:120 errors:0 dropped:0 overruns:0 frame:0
        TX packets:120 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:0
        RX bytes:6000 (5.8 KB)  TX bytes:6000 (5.8 KB)

vif3.0   Link encap:Ethernet  HWaddr fe:ff:ff:ff:ff:ff
        inet addr:10.0.0.129  Bcast:0.0.0.0  Mask:255.255.255.255
        inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link
        UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
        RX packets:9329 errors:0 dropped:0 overruns:0 frame:0
        TX packets:35119 errors:0 dropped:6 overruns:0 carrier:0
        collisions:0 txqueuelen:32
        RX bytes:509711 (497.7 KB)  TX bytes:56735424 (54.1 MB)

vif5.0    Link encap:Ethernet  HWaddr fe:ff:ff:ff:ff:ff
        inet addr:10.0.0.128  Bcast:0.0.0.0  Mask:255.255.255.255
        inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link
        UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
        RX packets:16411 errors:0 dropped:0 overruns:0 frame:0
        TX packets:40424 errors:0 dropped:5 overruns:0 carrier:0
        collisions:0 txqueuelen:32
        RX bytes:1378611 (1.3 MB)  TX bytes:57158876 (54.5 MB)

(vif3.0 and vif5.0 are node1 and node2, respectively)


> ifconfig on a domU
eth0      Link encap:Ethernet  HWaddr 00:16:3e:bf:d1:56
        inet addr:10.0.0.1  Bcast:10.0.0.255  Mask:255.255.255.0
        inet6 addr: fe80::216:3eff:febf:d156/64 Scope:Link
        UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
        RX packets:40489 errors:0 dropped:0 overruns:0 frame:0
        TX packets:16444 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:1000
        RX bytes:57164614 (54.5 MB)  TX bytes:1612287 (1.5 MB)

lo        Link encap:Local Loopback
        inet addr:127.0.0.1  Mask:255.0.0.0
        inet6 addr: ::1/128 Scope:Host
        UP LOOPBACK RUNNING  MTU:16436  Metric:1
        RX packets:0 errors:0 dropped:0 overruns:0 frame:0
        TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:0
        RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)



> route -n:  Kernel IP routing table on Dom0
Destination     Gateway         Genmask         Flags Metric Ref     
Use Iface
10.0.0.1        0.0.0.0         255.255.255.255 UH    0      0         
0 vif5.0
10.0.0.2        0.0.0.0         255.255.255.255 UH    0      0         
0 vif3.0
XXX.XXX.XXX.0   0.0.0.0         255.255.255.128 U     0      0         
0 eth0
224.0.0.0       0.0.0.0         240.0.0.0       U     0      0         
0 vif5.0
0.0.0.0         XXX.XXX.XXX.1   0.0.0.0         UG    0      0         
0 eth0
*Line 4 indicates the multicast route that was added between Dom0 and  
a DomU.
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