[CentOS] Basic KVM networking question

Dale Dellutri daledellutri at gmail.com
Mon Sep 10 13:06:03 EDT 2012


On Mon, Sep 10, 2012 at 11:34 AM, Steve Thompson <smt at vgersoft.com> wrote:
>
> A CentOS 6.3 box ("host") runs several KVM virtual machines, each of which
> has two interfaces attached to the two bridges br1 and br2 (and each thus
> has two IP's; one on 192.168.0.0/22 and one on 192.168.4.0/22);
> net.ipv4.ip_forward on the host is 1. Simplified diagram:
>
>                                 host
>                           +---------------+
>                           |               |
>    net1 = 192.168.0.0/22  |               |          net2 = 192.168.4.0/22
>    -----------------------+  br1      br2 +---------------------------------
>            |              |               |                |
>            |              |               |                |
>        Client A           +---------------+            Client B
>                         (hosts KVM1, KVM2, etc)
>
> Each client uses the bridge's IP address on the same side as default
> gateway. Client A can successfully ping or ssh (for example) to a KVM
> machine by IP address by using the KVM machine's net1 IP address. Client B
> can likewise communicate using the KVM machine's net2 IP address. However,
> neither client can communicate by using the address on the opposing
> segment (eg, Client A using KVM1_net2_IP); I can see from tcpdump that the
> packets are received by the virtual machine but no reply is ever made. Any
> clue?

Routing problem?  What are the response to each of the commands below on
all five systems: host, Client A and B, KVM1 and 2:

# ip addr show
# ip route show

-- 
Dale Dellutri


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