[ovs-discuss] Routing at the termination point
Abhishek Verma
abhishekv.verma at gmail.com
Fri Jul 17 16:49:46 UTC 2015
Hi Ben,
I understand its exasperating for you and other veterans to respond to
questions like forwarding not working, etc. However, i did enough googling
and i really couldnt, and am still unable to, figure out the real problem.
I am trying to see why the L3 packet is not going out and i see this:
I am constantly sending the ping traffic. As a result of that, i see the
following flow in the dataplane being created.
root at ip-172-31-1-48:~# ovs-dpctl dump-flows
skb_priority(0),tunnel(tun_id=0x258,src=52.27.111.115,dst=172.31.1.48,tos=0x0,ttl=53,flags(key)),in_port(4),skb_mark(0),eth(src=5e:21:e8:f3:44:6a,dst=06:45:1a:d2:1c:ed),eth_type(0x0800),ipv4(src=
8.8.8.1/0.0.0.0,dst=202.83.17.191/0.0.0.0,proto=1/0,tos=0/0,ttl=64/0,frag=no/0xff),
packets:1351, bytes:132398, used:0.340s, actions:1
Based on this flow i created a flow-rule which i expect the packet to
always hit:
root at ip-172-31-1-48:~# ovs-ofctl dump-flows ion1
NXST_FLOW reply (xid=0x4):
cookie=0x0, duration=26573.649s, table=0, n_packets=34881,
n_bytes=4025577, idle_age=0, priority=0 actions=NORMAL
cookie=0x0, duration=338.021s, table=0, n_packets=0, n_bytes=0,
idle_age=338, priority=500,ip,in_port=4,nw_dst=202.83.17.191
actions=output:2
However, for some reason i dont see my packets hitting the rule that i have
created.
This is strange since i created this based on the flow that was created in
the kernel.
Thanks, Abhishek
On Fri, Jul 17, 2015 at 8:36 PM, Ben Pfaff <blp at nicira.com> wrote:
> ### Q: I have a sophisticated network setup involving Open vSwitch, VMs or
> multiple hosts, and other components. The behavior isn't what I
> expect. Help!
>
> A: To debug network behavior problems, trace the path of a packet,
> hop-by-hop, from its origin in one host to a remote host. If
> that's correct, then trace the path of the response packet back to
> the origin.
>
> Usually a simple ICMP echo request and reply ("ping") packet is
> good enough. Start by initiating an ongoing "ping" from the origin
> host to a remote host. If you are tracking down a connectivity
> problem, the "ping" will not display any successful output, but
> packets are still being sent. (In this case the packets being sent
> are likely ARP rather than ICMP.)
>
> Tools available for tracing include the following:
>
> - "tcpdump" and "wireshark" for observing hops across network
> devices, such as Open vSwitch internal devices and physical
> wires.
>
> - "ovs-appctl dpif/dump-flows <br>" in Open vSwitch 1.10 and
> later or "ovs-dpctl dump-flows <br>" in earlier versions.
> These tools allow one to observe the actions being taken on
> packets in ongoing flows.
>
> See ovs-vswitchd(8) for "ovs-appctl dpif/dump-flows"
> documentation, ovs-dpctl(8) for "ovs-dpctl dump-flows"
> documentation, and "Why are there so many different ways to
> dump flows?" above for some background.
>
> - "ovs-appctl ofproto/trace" to observe the logic behind how
> ovs-vswitchd treats packets. See ovs-vswitchd(8) for
> documentation. You can out more details about a given flow
> that "ovs-dpctl dump-flows" displays, by cutting and pasting
> a flow from the output into an "ovs-appctl ofproto/trace"
> command.
>
> - SPAN, RSPAN, and ERSPAN features of physical switches, to
> observe what goes on at these physical hops.
>
> Starting at the origin of a given packet, observe the packet at
> each hop in turn. For example, in one plausible scenario, you
> might:
>
> 1. "tcpdump" the "eth" interface through which an ARP egresses
> a VM, from inside the VM.
>
> 2. "tcpdump" the "vif" or "tap" interface through which the ARP
> ingresses the host machine.
>
> 3. Use "ovs-dpctl dump-flows" to spot the ARP flow and observe
> the host interface through which the ARP egresses the
> physical machine. You may need to use "ovs-dpctl show" to
> interpret the port numbers. If the output seems surprising,
> you can use "ovs-appctl ofproto/trace" to observe details of
> how ovs-vswitchd determined the actions in the "ovs-dpctl
> dump-flows" output.
>
> 4. "tcpdump" the "eth" interface through which the ARP egresses
> the physical machine.
>
> 5. "tcpdump" the "eth" interface through which the ARP
> ingresses the physical machine, at the remote host that
> receives the ARP.
>
> 6. Use "ovs-dpctl dump-flows" to spot the ARP flow on the
> remote host that receives the ARP and observe the VM "vif"
> or "tap" interface to which the flow is directed. Again,
> "ovs-dpctl show" and "ovs-appctl ofproto/trace" might help.
>
> 7. "tcpdump" the "vif" or "tap" interface to which the ARP is
> directed.
>
> 8. "tcpdump" the "eth" interface through which the ARP
> ingresses a VM, from inside the VM.
>
> It is likely that during one of these steps you will figure out the
> problem. If not, then follow the ARP reply back to the origin, in
> reverse.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://openvswitch.org/pipermail/ovs-discuss/attachments/20150717/06141463/attachment-0002.html>
More information about the discuss
mailing list