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Caprisun
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PostPosted: Tue Dec 18, 2012 4:33 am    Post subject: Multicast forwarding for Bridge? (KVM) Reply with quote

Hello,

I have recently begun a new amd64 build of Gentoo for a KVM Host.

Using the following config for net.br0 under /etc/conf.d/net:

Code:
#config_eth0="192.168.1.113 netmask 255.255.255.0 brd 192.168.1.255"
#routes_eth0="default via 192.168.1.1"


# Ethernet Bridge br0
bridge_br0="eth0"
brctl_br0="setfd 0 sethello 0 stp off"

config_br0="192.168.1.113/24"
routes_br0="default via 192.168.1.1"

# Ethernet Dummy
config_eth0="null"


Windows 2k3 Server and Gentoo guests can get online and perform updates etc.

However the DHCP Service on Windows seems to be deaf...

ipv4 forwarding ==1

mc_forwarding is == 0, with denied permissions when I attempted to change via sysctl and manual manipulation.

I have multicasting options set in the kernel as built in.

Code:
KVM linux # more .config | grep MULTI
CONFIG_NEED_MULTIPLE_NODES=y
CONFIG_IP_MULTICAST=y
CONFIG_IP_MULTIPLE_TABLES=y
CONFIG_IP_ROUTE_MULTIPATH=y
CONFIG_IP_MROUTE_MULTIPLE_TABLES=y
# CONFIG_IPV6_MULTIPLE_TABLES is not set
# CONFIG_NET_SCH_MULTIQ is not set
# CONFIG_SCSI_MULTI_LUN is not set
CONFIG_DEVPTS_MULTIPLE_INSTANCES=y
# CONFIG_HID_MULTITOUCH is not set


I would greatly appreciate assistance, I'm building this setup with a diskless Dell 620 to showcase KVM for virtualized environments using diskless systems. KVM is using an Intel SSD with ext4.

It seems like this is the only traffic not behaving normally. I'm not using iptables or any other firewall.

The KVM Guest's are using Virtio drivers connected to br0. I notice that libvirt creates a vnet* interface for each one and joins it to br0.

Code:
KVM linux # brctl show
bridge name   bridge id      STP enabled   interfaces
br0      8000.bc305bde899c   no      eth0
                     vnet0
                     vnet1
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PostPosted: Tue Dec 18, 2012 1:29 pm    Post subject: Reply with quote

use a milticast mac address.

from wikipedia:

Quote:
Ethernet

Ethernet frames with a value of 1 in the least-significant bit of the first octet[note 2] of the destination address are treated as multicast frames and are flooded to all points on the network. While frames with ones in all bits of the destination address (FF:FF:FF:FF:FF:FF) are sometimes referred to as broadcasts, Ethernet network equipment generally does not distinguish between multicast and broadcast frames. Modern Ethernet controllers filter received packets to reduce CPU load, by looking up the hash of a multicast destination address in a table, initialized by software, which controls whether a multicast packet is dropped or fully received.
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Caprisun
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PostPosted: Tue Dec 18, 2012 2:51 pm    Post subject: Reply with quote

________________________0 wrote:
use a milticast mac address.

from wikipedia:

Quote:
Ethernet

Ethernet frames with a value of 1 in the least-significant bit of the first octet[note 2] of the destination address are treated as multicast frames and are flooded to all points on the network. While frames with ones in all bits of the destination address (FF:FF:FF:FF:FF:FF) are sometimes referred to as broadcasts, Ethernet network equipment generally does not distinguish between multicast and broadcast frames. Modern Ethernet controllers filter received packets to reduce CPU load, by looking up the hash of a multicast destination address in a table, initialized by software, which controls whether a multicast packet is dropped or fully received.


I'm assuming DHCP requests are already following this scheme...

My question is, how can I stop these packets from being dropped once they hit the br0 interface?

It seems like I need to enable Multicast forwarding, but the system will not allow me. I'm not sure what I'm missing, but I'll keep reading.
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PostPosted: Tue Dec 18, 2012 6:29 pm    Post subject: set up? Reply with quote

what's your set up like?

router -> machine with br -> guests??

probably use dhcp on the bridge. did you double check if you have a dhcp package installed?
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Caprisun
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PostPosted: Tue Dec 18, 2012 6:39 pm    Post subject: Re: set up? Reply with quote

________________________0 wrote:
what's your set up like?

router -> machine with br -> guests??

probably use dhcp on the bridge. did you double check if you have a dhcp package installed?


Pretty much.

I have a router, a switch, and a Dell 960 running KVM with a br0. There's a Dell 620 connected to the switch, and I would like it to be able to obtain a DHCP address from a KVM guest so that it can boot without a disk.

Do you mean running a DHCP Server in Linux? It seems like I should be able to make a guest do it...

I've been seeing things like adding a route for 224.0.0.0, is this obsolete or still relevant? I haven't found a daemon to do multicast routing or a way to enable mc_forwarding under sysctl.

EDIT:

I also disabled RP_FILTER. It did not change anything.

When I get home I'm also going to verify that my network driver is correct...
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Caprisun
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PostPosted: Wed Dec 19, 2012 11:47 pm    Post subject: Re: set up? Reply with quote

Caprisun wrote:
________________________0 wrote:
what's your set up like?

router -> machine with br -> guests??

probably use dhcp on the bridge. did you double check if you have a dhcp package installed?


Pretty much.

I have a router, a switch, and a Dell 960 running KVM with a br0. There's a Dell 620 connected to the switch, and I would like it to be able to obtain a DHCP address from a KVM guest so that it can boot without a disk.

Do you mean running a DHCP Server in Linux? It seems like I should be able to make a guest do it...

I've been seeing things like adding a route for 224.0.0.0, is this obsolete or still relevant? I haven't found a daemon to do multicast routing or a way to enable mc_forwarding under sysctl.

EDIT:

I also disabled RP_FILTER. It did not change anything.

When I get home I'm also going to verify that my network driver is correct...


So after verifying the drivers, and monitoring TCPdump, the KVM Host is receiving the DHCP requests. They are not making their way to the DHCP Server Virtual Machine, which can access the internet and network normally...

EDIT:

After running tcpdump on my PXE boot VM, i can see the broadcasts coming through! This VM is on the same KVM host using the same br0!

But my Windows 2k3 Server is still deaf...

I'm experimenting with the different network adaptors at the moment.
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Caprisun
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PostPosted: Sun Dec 23, 2012 5:45 pm    Post subject: Reply with quote

After some configuring, the Gentoo Guest VM is handing out DHCP addresses normally.

I must assume something was wrong with the Windows Server...
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