On Fri, Jun 24, 2016 at 10:06:26AM +0530, sree ietf wrote:
> Hi,
>
> This is my topology :
>
> S1 and S2 are openvswitches.
>
> Link { h1-eth1 <--------> s1-eth1 } connected to S1 Switch.
> Link { s1-trunk <--------> s2-trunk } connected in between S1 and S2.
> Link { s2-eth1 <--------> h3-eth1 } connected to S2 Switch.
>
> Switch S1 has s1-eth1 and s1-trunk.
> Switch S2 has s2-eth1 and s2-trunk.
>
>
> h1-eth1: 192.168.10.1/24
> h3-eth1: 192.168.10.4/24
>
> 1. I'm trying to ping from h1-eth1 to h3-eth1
> 2. I'm running tcpdump on h3-eth1, though ping is successful, i don't see
> any
> ping/icmp packets at h3-eth1
> 3. But when I ping an another ip-address in the same subnet which is not
> configured, such as 192.168.10.222/24, I can able to see ARP requests
> in
> tcpdump at h3-eth1.
>
> Why I am not able to see any packets in tcpdump when ping is success?
>
> please shed some light.
I don't understand your description of the topology.
At a guess, you might expect Linux to bind an IP address to a particular
interface. It doesn't work that way. The FAQ illustrates one case:
### Q: I configured one IP address on VLAN 0 and another on VLAN 9, like
this:
ovs-vsctl add-br br0
ovs-vsctl add-port br0 eth0
ifconfig br0 192.168.0.5
ovs-vsctl add-port br0 vlan9 tag=9 -- set interface vlan9 type=internal
ifconfig vlan9 192.168.0.9
but other hosts that are only on VLAN 0 can reach the IP address
configured on VLAN 9. What's going on?
A: RFC 1122 section 3.3.4.2 "Multihoming Requirements" describes two
approaches to IP address handling in Internet hosts:
- In the "Strong ES Model", where an ES is a host ("End
System"), an IP address is primarily associated with a
particular interface. The host discards packets that arrive
on interface A if they are destined for an IP address that is
configured on interface B. The host never sends packets from
interface A using a source address configured on interface B.
- In the "Weak ES Model", an IP address is primarily associated
with a host. The host accepts packets that arrive on any
interface if they are destined for any of the host's IP
addresses, even if the address is configured on some
interface other than the one on which it arrived. The host
does not restrict itself to sending packets from an IP
address associated with the originating interface.
Linux uses the weak ES model. That means that when packets
destined to the VLAN 9 IP address arrive on eth0 and are bridged to
br0, the kernel IP stack accepts them there for the VLAN 9 IP
address, even though they were not received on vlan9, the network
device for vlan9.
To simulate the strong ES model on Linux, one may add iptables rule
to filter packets based on source and destination address and
adjust ARP configuration with sysctls.
BSD uses the strong ES model.
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