[pve-devel] BUG in vlan aware bridge

Josef Johansson josef at oderland.se
Wed Oct 13 13:36:59 CEST 2021


Hi,

AFAIK it's netfilter that is doing defragmenting so that it can firewall.

If you specify

iptables -t raw -I PREROUTING -s 77.244.240.131 -j NOTRACK

iptables -t raw -I PREROUTING -s 37.16.72.52 -j NOTRACK

you should be able to make it ignore your packets.


As a datapoint I could ping fine from a MTU 1500 host, over MTU 9000
vlan-aware bridges with firewalls to another MTU 1500.

As you would assume the package is defragmented over MTU 9000 links and
fragmented again over MTU 1500 devices.

Med vänliga hälsningar
Josef Johansson

On 10/13/21 11:22, VELARTIS Philipp Dürhammer wrote:
> HI,
>
>
> Yes i think it has nothing to do with the bonds but with the vlan aware bridge interface.
>
> I see this with ping -s 1500
>
> On tap interface: 
> 11:19:35.141414 62:47:e0:fe:f9:31 > 54:e0:32:27:6e:50, ethertype IPv4 (0x0800), length 1514: (tos 0x0, ttl 64, id 39999, offset 0, flags [+], proto ICMP (1), length 1500)
>     37.16.72.52 > 77.244.240.131: ICMP echo request, id 2182, seq 4, length 1480
> 11:19:35.141430 62:47:e0:fe:f9:31 > 54:e0:32:27:6e:50, ethertype IPv4 (0x0800), length 562: (tos 0x0, ttl 64, id 39999, offset 1480, flags [none], proto ICMP (1), length 548)
>     37.16.72.52 > 77.244.240.131: ip-proto-1
>
> On vmbr0:
> 11:19:35.141442 62:47:e0:fe:f9:31 > 54:e0:32:27:6e:50, ethertype 802.1Q (0x8100), length 2046: vlan 350, p 0, ethertype IPv4 (0x0800), (tos 0x0, ttl 64, id 39999, offset 0, flags [none], proto ICMP (1), length 2028)
>     37.16.72.52 > 77.244.240.131: ICMP echo request, id 2182, seq 4, length 2008
>
> On bond0 its gone....
>
> But who is in charge of fragementing the packets normally? The bridge itself? Netfilter?
>
> -----Ursprüngliche Nachricht-----
> Von: pve-devel <pve-devel-bounces at lists.proxmox.com> Im Auftrag von Stoyan Marinov
> Gesendet: Mittwoch, 13. Oktober 2021 00:46
> An: Proxmox VE development discussion <pve-devel at lists.proxmox.com>
> Betreff: Re: [pve-devel] BUG in vlan aware bridge
>
> OK, I have just verified it has nothing to do with bonds. I get the same behavior with vlan aware bridge, bridge-nf-call-iptables=1 with regular eth0 being part of the bridge. Packets arrive fragmented on tap, reassembled by netfilter and then re-injected in bridge assembled (full size).
>
> I did have limited success by setting net.bridge.bridge-nf-filter-vlan-tagged to 1. Now packets seem to get fragmented on the way out and back in, but there are still issues:
>
> 1. I'm testing with ping -s 2000 (1500 mtu everywhere) to an external box. I do see reply packets arrive on the vm nic, but ping doesn't see them. Haven't analyzed much further.
> 2. While watching with tcpdump (inside the vm) i notice "ip reassembly time exceeded" messages being generated from the vm.
>
> I'll try to investigate a bit further tomorrow.
>
>> On 12 Oct 2021, at 11:26 PM, Stoyan Marinov <stoyan at marinov.us> wrote:
>>
>> That's an interesting observation. Now that I think about it, it could be caused by bonding and not the underlying device. When I tested this (about an year ago) I was using bonding on the mlx adapters and not using bonding on intel ones.
>>
>>> On 12 Oct 2021, at 3:36 PM, VELARTIS Philipp Dürhammer <p.duerhammer at velartis.at> wrote:
>>>
>>> HI,
>>>
>>> we use HP Server with Intel Cards or the standard hp nic ( ithink also intel)
>>>
>>> Also I see the I did a mistake:
>>>
>>> Setup working:
>>> tapX (UNtagged) <- -> vmbr0 <- - > bond0
>>>
>>> is correct. (before I had also tagged) 
>>>
>>> it should be :
>>>
>>> Setup not working:
>>> tapX (tagged) <- -> vmbr0 <- - > bond0
>>>
>>> Setup working:
>>> tapX (untagged) <- -> vmbr0 <- - > bond0
>>>
>>> Setup also working:
>>> tapX < - - > vmbr0v350 < -- > bond0.350 < -- > bond0
>>>
>>> -----Ursprüngliche Nachricht-----
>>> Von: pve-devel <pve-devel-bounces at lists.proxmox.com> Im Auftrag von Stoyan Marinov
>>> Gesendet: Dienstag, 12. Oktober 2021 13:16
>>> An: Proxmox VE development discussion <pve-devel at lists.proxmox.com>
>>> Betreff: Re: [pve-devel] BUG in vlan aware bridge
>>>
>>> I'm having the very same issue with Mellanox ethernet adapters. I don't see this behavior with Intel nics. What network cards do you have?
>>>
>>>> On 12 Oct 2021, at 1:48 PM, VELARTIS Philipp Dürhammer <p.duerhammer at velartis.at> wrote:
>>>>
>>>> HI,
>>>>
>>>> i am playing around since days because we have strange packet losses.
>>>> Finally I can report following (Linux 5.11.22-4-pve, Proxmox 7, all devices MTU 1500):
>>>>
>>>> Packet with sizes > 1500 without VLAN working well but at the moment they are Tagged they are dropped by the bond device.
>>>> Netfilter (set to 1) always reassembles the packets when they arrive a bridge. But they don't get fragmented again I they are VLAN tagged. So the bond device drops them. If the bridge is NOT Vlan aware they also get fragmented and it works well.
>>>>
>>>> Setup not working:
>>>>
>>>> tapX (tagged) <- -> vmbr0 <- - > bond0
>>>>
>>>> Setup working:
>>>>
>>>> tapX (tagged) <- -> vmbr0 <- - > bond0
>>>>
>>>> Setup also working:
>>>>
>>>> tapX < - - > vmbr0v350 < -- > bond0.350 < -- > bond0
>>>>
>>>> Have you got any idea where to search? I don't understand who is in charge of fragmenting packages again if they get reassembled by netfilter. (and why it is not working with vlan aware bridges)
>>>>
>>>>
>>>> _______________________________________________
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>>>> pve-devel at lists.proxmox.com
>>>> https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel
>>>>
>>>
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