Bridge woes

[D'Arcy Cain]

On 10/27/20 2:58 PM, Michael Gmelin wrote:

I hope you don't mind but I reverted this conversation back to the list in 
case it gives someone else any ideas.

> Hi,
> 
> I tried to reproduce the problem on my home network, but things just
> work as expected.
> 
> I could run VMs with IPs off the local network, fixed ones as well as
> DHCP.
> 
> The topology looks a bit different:
> vm->server->router ->(nat)-> internet
>       |
>       + dhcp/dns

I suppose that that is essentially the same but let me see if I get it.  You 
have a network, say 192.168.1.0/24, behind your NAT router.  You have 
physical servers like 192.168.1.1 and 192.168.1.2 on this network.  You then 
put a VM on the  .1 host numbered 192.168.1.3 and it can connect to 
192.168.1.2.  Is that correct?

> I would speculate that there's either something going on with
> the switch (you might want to take a look at it), or you're experiencing
> some sort of asymmetric routing issue (ping/icmp is usually just fine

Not sure what that could be.  It's not just a problem with external hosts. 
Hosts on the same network are also showing the symptoms.  Another point is 
that I can access it inbound.  It's only outbound connections that don't work.

> with that). Or it might be something with the bge driver (I'm using em

The only server that it can connect to is running bce.  I have some em 
servers but it doesn't connect to those.

> here). I assume you already tried disabling all sorts of offloading to
> see if it makes a difference?

Yep.  I tried -tso -lro -rxcsum -rxcsum6 -txcsum -txcsum6 -vlanhwtag 
-vlanhwtso and subsets of that.

> Other than that I would suggest to play with tcpdump to see if packets
> are returned on the same interface they've been sent out on or not.

Here is an example packet seen on the host:

11:20:40.397067 IP 98.158.139.71.44448 > 98.158.139.66.22: Flags [S], seq 
3285763868, win 65535, options [mss 1460,nop,wscale 6,sackOK,TS val 
3003762262 ecr 0], length 0

The .66 never sees the packet and the host never sees a return packet.  On 
the other hand, a connection attempt from .66 to the VM shows up properly.


> Proxy arp might play a role on a local network, that's something I've
> seen in the past when I has hosts with multiple interfaces on the same
> (multiple) networks. If you can afford to try it, I would see if
> shutting down eth1 (and then flushing all arp tables on all
> hosts/devices involved in your test) makes a difference[0].

I want to be careful about dropping eth1 as it is the only way in if I mess 
up eth0.

-- 
D'Arcy J.M. Cain <darcy at druid.net>         |  Democracy is three wolves
http://www.druid.net/darcy/                |  and a sheep voting on
+1 416 788 2246     (DoD#0082)    (eNTP)   |  what's for dinner.
IM: darcy at VybeNetworks.com, VoIP: sip:darcy at druid.net

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