[Lxc-users] Slow response times (at least, from the LAN) to LXC containers

Daniel Lezcano daniel.lezcano at free.fr
Thu Mar 11 20:45:05 UTC 2010

Michael B. Trausch wrote:
> On 03/10/2010 12:06 PM, Daniel Lezcano wrote:
>> Michael B. Trausch wrote:
>>> Here is ping output showing the problem:
>>> mbt at fennel:~$ time ping -c 4 spicerack.trausch.us
>>> PING spicerack.trausch.us ( 56(84) bytes of data.
>>> From icmp_seq=2 Redirect Host(New nexthop:
>>> From icmp_seq=3 Redirect Host(New nexthop:
>>> 64 bytes from icmp_seq=4 ttl=64 time=2.27 ms
>>> --- spicerack.trausch.us ping statistics ---
>>> 4 packets transmitted, 1 received, 75% packet loss, time 11073ms
>>> rtt min/avg/max/mdev = 2.278/2.278/2.278/0.000 ms
>>> real 0m21.144s
>>> user 0m0.000s
>>> sys 0m0.020s
>>> Now, this is pinging from my laptop. When I ping from the outside
>>> world, it always seems to work:
>> Mmh, some informations are missing to investigate.
>> The redirect you receive means the router find an optimized route for
>> the packet you sent to him, so the icmp redirect will trigger the kernel
>> to create a new route for these packets. Maybe the route is not created
>> in the right container ? Can you check where is created this route ?
>> * ip route table show all
>> or
>> * route -Cn
> The routing tables are automatically setup (that is, they are setup by 
> Debian's /etc/network/interfaces) based on the network configuration 
> information.
> Here is the routing table from the spicerack.trausch.us container:
> mbt at spicerack:~$ ip route show all
> dev eth0  proto kernel  scope link  src
> dev eth1  proto kernel  scope link  src
> default via dev eth0  metric 100
> Here is the routing table from the container's host:
> mbt at saffron:~$ ip route show all
> dev br0  proto kernel  scope link  src
> dev virbr0  proto kernel  scope link  src
> default via dev br0  metric 100

What I would like to see is the route cache (so the ouput of "ip route 
show table all"). The icmp redirect will create a specific route, I 
would like to see where it is created.

Ok at this point I still have not enough information, let's summarize:

1 - you have a router with two nics. One is the internet side with and the other one is connected to the lan with, right ?

2 - you have a host 'saffron' with the ip address (ip 
forwarding is set and nat is enabled), right ?

3 - you have in this host a container 'spicerack' with two virtualized 
interfaces, the first one has set and the second one has set, right ?

4 - you have another host plugged on the lan called 'fennel', when you 
ping the container from this host, you receive an icmp redirect and 
packets are lost, right ?

  - what are the ip address / routes of 'fennel' ?

>> Can you give a summary of the network topolgy (IP of each container and
>> routes ) ?
> The network router has the global IP address and an 
> address on the LAN of  It is an unfortunate piece of 
> hardware supplied by my ISP (it is a cable modem and router 
> combination).  I have a /29 from my ISP, of which they use one address 
> (.190) and I use the other 5 (.185 through .189).  Anything that 
> doesn't have a static IP address has a address, and is 
> NAT'd through .190.
>> For example, where is located ?
> It is at the network edge, and as noted above has also the global IP 
> address
>> Is your host configured as a router ?
> The LXC host has IPv4 forwarding enabled:
> mbt at saffron:~$ cat /proc/sys/net/ipv4/conf/all/forwarding
> 1
> Interestingly enough, IPv6 forwarding was _not_ enabled on the host 
> node, despite the fact that I am pretty sure that I enabled it.  It is 
> enabled now, though:
> mbt at saffron:~$ cat /proc/sys/net/ipv6/conf/all/forwarding
> 1
>> Probably more questions will come later :)
> Okay, that's fine.  I will answer anything/everything I can.  As far 
> as I can tell, I am only having this problem on the LAN when I try to 
> reach one of the global IP addresses.  Unfortunately, that's the most 
> annoying part.  Most of my things on those addresses are things that I 
> use mostly at home, but sometimes need to use out and about, which is 
> why they are on my Web server in the first place.  :-)
>>> What I don't get is why I am receiving these redirects from ping. I
>>> never get them when pinging 172.16.0.x addresses that are in LXC
>>> containers on that system. And I never got these redirects before when
>>> I was running containers in OpenVZ.
>>> Also, if I try to ping that same interface's IPv6 addresses, I get
>>> failures (Address unreachable), no matter if I ping the private or the
>>> global one. However, I can reach ipv6.google.com just fine, and it is
>>> going through that computer to get to my tunnel to Hurricane Electric.
>>> It has to, since that container is my only IPv6 route to the world and
>>> the tunnel endpoint is that container's global IP address.
> It seems that this issue might be fixed; I guess the host system 
> didn't remember to enable forwarding after the last reboot.  Though 
> that is even more confusing:  IPv6 forwarding should not be required 
> on the host to ping an Ethernet interface on the bridge that has IPv6, 
> because the host should not have to forward that.  Only a container 
> should need the IPv6 forwarding enabled if the container is the thing 
> that is routing between your own IPv6 network and the IPv6 Internet.
>>> I am completely confused on this one. I don't know where to look next.
> >
>> Let's try to solve the problems one by one.

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