[ovs-discuss] MPLS double POP bug?

Stefano Salsano stefano.salsano at uniroma2.it
Mon Nov 24 17:49:06 UTC 2014


Il 21/11/2014 11:04, Stefano Salsano ha scritto:
> Il 12/11/2014 01:19, Ben Pfaff ha scritto:
>> On Tue, Nov 11, 2014 at 11:25:34PM +0100, Stefano Salsano wrote:
>>> we need to POP out two MPLS labels in an egress node and then send
>>> out the packet as plain IP packet, but apparently this is not
>>> working in Open vSwitch v2.390 operating in kernel mode
>

[...]
>
> we are now trying to add the correct check in compose_mpls_pop_action:
>
> } else if (n >= ctx->xbridge->max_mpls_depth) {
> COVERAGE_INC(xlate_actions_mpls_overflow);
> ctx->xout->slow |= SLOW_ACTION;
> }
>
> and we will let you know the results

Hi all,

we added the if condition that forwards the packet to user space (slow 
path) in case of POP with multiple MPLS labels (see patch attached)

the result is that the packet is correctly forwarded, but there is a 
problem in updating the stats

unfortunately we do not have a clear picture of the architecture, but we 
see that both the "handler" thread and the "revalidator" thread process 
the flow

the "revalidator" thread returns this error message: "resubmit actions 
recursed over 64 times"

it seems that the both the handler and revalidator thread receive as 
input this flow description:

mpls,in_port=4,vlan_tci=0x0000,dl_src=5a:93:39:89:21:cf,dl_dst=22:4e:63:a1:65:37,
mpls_label=524292,mpls_tc=0,mpls_ttl=64,mpls_bos=0,mpls_lse1=0,mpls_lse2=0

which according to us is wrong, as we see two inner mpls labels set set to 0

the correct flow in our opinion should be like this (that we have taken 
from a debug print in the handler thread)
mpls,in_port=1,vlan_tci=0x0000,dl_src=5a:93:39:89:21:cf,dl_dst=22:4e:63:a1:65:37,
mpls_label=524292,mpls_tc=0,mpls_ttl=64,mpls_bos=0,mpls_lse1=1073742144

it seems that the odp_flow_key_to_flow__ function 
(https://github.com/openvswitch/ovs/blob/master/lib/odp-util.c#L3590) is 
not able to retrieve the correct flow both in the handler and in the 
revalidator thread (result = ODP_FIT_TOO_LITTLE)

in the handler thread the function flow_extract is called afterwards 
(https://github.com/openvswitch/ovs/blob/master/ofproto/ofproto-dpif-upcall.c#L634), 
setting the correct flow information and allowing the forwarding of the 
packet, while in the validator thread this does not happen and the 
validator is stuck with the wrong flow information

do you have any hint on how we can fix the problem ??

thank you
Stefano & Pier Luigi



>
>
> *****************************************************************
> Detailed Report of the problem sent on 18/11/2014
>
> 1) recirculation does not work properly when there are
> two or more mpls_pop, let us compare what happens in our system when
> using the kernel datapath (not working) or the userspace netdev datapath
> (working)
>
> we are using this reference topology
> h1---peo1----peo2---h2
> h1 source node, peo1 ingress node, peo2 egress node, h2 dest node
>
> in peo1, we report the rules shown with ovs-ofctl (obviously they are
> the same with kernel and netdev datapath)
>
> peo1:
> -> cookie=0x0, duration=185.672s, table=0, n_packets=178, n_bytes=17444,
> ip,in_port=2
> actions=push_mpls:0x8847,set_field:262144->mpls_label,push_mpls:0x8847,set_field:524292->mpls_label,goto_table:1
>
> -> cookie=0x0, duration=185.617s, table=1, n_packets=178, n_bytes=17444,
> mpls,in_port=2,mpls_label=524292 actions=output:1
>
> recirculation causes the installation of flows that are not visible with
> the ovs-ofctl command, so we use ovs-appctl
> (sudo ovs-appctl dpif/dump-flows peo1)
>
> the result is different with kernel and netdev datapath:
>
> kernel datapath:
> -> recirc_id(0),in_port(2),eth_type(0x0800),
> ipv4(tos=0/0xfc,ttl=64,frag=no), packets:14, bytes:1372, used:0.692s,
> actions:userspace(pid=4294959673,slow_path(action))
>
> netdev datapath:
> -> recirc_id(0),in_port(2),eth_type(0x0800),
> ipv4(tos=0/0xfc,ttl=64,frag=no), packets:17, bytes:1666, used:0.664s,
> actions:push_mpls(label=262144,tc=0,ttl=64,bos=1,eth_type=0x8847),push_mpls(label=524292,tc=0,ttl=64,bos=0,eth_type=0x8847),1
>
>
> we note that with kernel datapath, there is a fallback to userspace
> processing that is triggered when multiple PUSH operation are requested
>
> in peo2, we report the rules shown with ovs-ofctl (obviously they are
> the same with kernel and netdev datapath)
>
> peo2:
> -> cookie=0x0, duration=621.359s, table=0, n_packets=284, n_bytes=30104,
> mpls,in_port=1 actions=goto_table:1
> ->  cookie=0x0, duration=621.299s, table=1, n_packets=284,
> n_bytes=30104, mpls,in_port=1,mpls_label=524292
> actions=pop_mpls:0x8847,resubmit(,1)
> -> cookie=0x0, duration=621.184s, table=1, n_packets=284, n_bytes=30104,
> mpls,in_port=1,mpls_label=262144,mpls_bos=1
> actions=pop_mpls:0x0800,output:2
>
> recirculation causes the installation of flows that are not visible with
> the ovs-ofctl command, so we use ovs-appctl
> (sudo ovs-appctl dpif/dump-flows peo1)
>
> the result is different with kernel and netdev datapath:
>
> kernel datapath:
> NO RULES ARE SHOWN !!!!
>
> netdev datapath:
> -> recirc_id(0),in_port(4),eth_type(0x8847),
> mpls(lse0=0x80004040/0xfffff100, lse1=0x40000140/0xffffffff),
> packets:5, bytes:530, used:0.720s,
> actions:pop_mpls(eth_type=0x8847),pop_mpls(eth_type=0x800),5
>
> peo2 is the egress node where we execute the double pop, it seems that
> something is preventing the installation of the "recirculation" flows
> when using the kernel datapath
>
> We have also checked the ovs-vswitchd log and when we activate the
> kernel datapath, we see these warning messages:
>
> -> |WARN|system at ovs-system: failed to put[create] (Invalid argument)
> recirc_id(0),dp_hash(0/0),skb_priority(0/0),in_port(4),skb_mark(0/0),eth(src=e6:da:61:3a:f5:81/00:00:00:00:00:00,dst=0a:a5:58:7d:1c:12/00:00:00:00:00:00),eth_type(0x8847),mpls(label=524292/0xfffff,tc=0/0,ttl=64/0x0,bos=0/1),
>
> actions:pop_mpls(eth_type=0x8847),pop_mpls(eth_type=0x800),5
> -> |WARN|system at ovs-system: execute pop_mpls(eth_type=0x8847),
> pop_mpls(eth_type=0x800),5 failed
> (Invalid argument) on packet mpls,in_port=0,vlan_tci=0x0000,
> dl_src=e6:da:61:3a:f5:81,dl_dst=0a:a5:58:7d:1c:12,mpls_label=524292,
> mpls_tc=0,mpls_ttl=64,mpls_bos=0,mpls_lse1=1073742144
>
> These messages explain also the absence of the "recirculation flows",
> even if in our mininet emulation scenario there is a single ovs-vswitchd
> instance, we can refer these messages to peo2 from the "output port"
>
> We also noted at the beginning of the vswitchd-log these messages:
>
> When using the Kernel datapath:
> 2014-11-17T19:09:23.698Z|00029|ofproto_dpif|INFO|system at ovs-system:
> MPLS label stack length probed as 1
>
> When using the userspace netdev datapath:
> 2014-11-17T19:17:37.697Z|00069|ofproto_dpif|INFO|netdev at ovs-netdev:
> MPLS label stack length probed as 3
>
> We have checked in the ovs code, this print is generated by the
> function static size_t check_max_mpls_depth(struct dpif_backer
> *backer), this function tries to probe the stack length...
>
> we would like to understand what is behind this limitation... why in our
> system the stack length for the kernel datapath is limited to 1 ?
> does the stack length depend on some features provided by the
> system/kernel? is there some kernel version without this limitation?
>
> assuming that we have this limitation, our understanding is that this
> control does not prevent to PUSH three mpls label because the packet is
> sent to the userspace ovs-switchd as a fallback (and the packet is
> correctly created and forwarded)... is this correct?
>
> if this is the case, it seems that the same fallback is not activated in
> case of multiple POP operations (>=2 POPs) the system tries to execute
> the multiple POPs in the kernel but it generates the error messages
> listed above and no packet is forwarded
>
>
> End Detailed Report of the problem
> *****************************************************************
>
>
>
>
>
>
>
>
>>>
>>> We have replicated the problem in a simple mininet setup (script
>>> attached) with four nodes connected as follows:
>>>
>>> h1---peo1----peo2---h2
>>> h1 source node, peo1 ingress node, peo2 egress node, h2 dest node
>>>
>>> - h1 pings h2 (automatic static arp table are used, so there is no ARP)
>>> - peo1 pushes two mpls labels in the packet
>>> - peo2 is supposed to pop the two labels and forward the packet as IP
>>>
>>> we have a rule to match the outer label, POP it and resubmit as MPLS
>>> packet:
>>> actions=pop_mpls:0x8847,resubmit(,1)
>>>
>>> then we have a rule to match the inner label,  POP it and output on
>>> a port as an IP packet:
>>> actions=pop_mpls:0x0800,output:11
>>>
>>> both rules match (and the first pop works), but then the packet
>>> does not exit from the port 11
>>>
>>> we have also tried without success to recirculate the packet
>>> implicitly after the first pop, replacing the first action with:
>>> actions=pop_mpls:0x8847
>>>
>>> Can anyone help us to identify the problem ? Are we doing something
>>> wrong or is it a bug?
>>>
>>> The mininet script to setup the topology and create the rules in
>>> order to reproduce the problem is attached.
>>>
>>> Some details are reported hereafter for the scenario with explicit
>>> resubmit.
>>>
>>> thank you in advance for your help...
>>>
>>> ciao
>>> Stefano
>>>
>>> - peo1 flow table
>>> OFPST_FLOW reply (OF1.3) (xid=0x2):
>>> duration=275.553s, table=0, n_packets=58, n_bytes=5684,ip,in_port=2
>>> actions=push_mpls:0x8847,set_field:262144->mpls_label,push_mpls:0x8847,set_field:524292->mpls_label,goto_table:1
>>>
>>>
>>> duration=275.493s,table=1,n_packets=58,n_bytes=5684,mpls,in_port=2,mpls_label=524292
>>>
>>> actions=output:1
>>>
>>> - peo2 flow table
>>> OFPST_FLOW reply (OF1.3) (xid=0x2):
>>>
>>> duration=317.678s,table=0,n_packets=58,n_bytes=6148,mpls,in_port=1
>>> actions=goto_table:1
>>>
>>> duration=317.618s,table=1,n_packets=58,n_bytes=6148,mpls,in_port=1,mpls_label=524292
>>>
>>> actions=pop_mpls:0x8847,resubmit(,1)
>>>
>>> duration=317.559s,table=1,n_packets=58,n_bytes=6148,mpls,in_port=1,mpls_label=262144,mpls_bos=1
>>>
>>> actions=pop_mpls:0x0800,output:2
>>>
>>> NB If the interfaces created by Mininet in the root namespace happen
>>> to be down, stop the Network Manager and then restart the experiment
>>> --
>>> *******************************************************************
>>> Stefano Salsano
>>> Professore Associato
>>> Dipartimento Ingegneria Elettronica
>>> Universita' di Roma Tor Vergata
>>> Via del Politecnico, 1 - 00133 Roma - ITALY
>>>
>>> http://netgroup.uniroma2.it/Stefano_Salsano/
>>>
>>> E-mail  : stefano.salsano at uniroma2.it
>>> Cell.   : +39 320 4307310
>>> Office  : (Tel.) +39 06 72597770  (Fax.) +39 06 72597435
>>> *******************************************************************
>>>
>>
>>> #!/usr/bin/python
>>>
>>> import subprocess
>>>
>>> from mininet.net import Mininet
>>> from mininet.node import Host, OVSKernelSwitch, Node
>>> from mininet.cli import CLI
>>> from mininet.log import lg, info
>>>
>>> def setup():
>>>
>>>     lg.setLogLevel('info')
>>>
>>>     net = Mininet(switch=OVSKernelSwitch, build=False,
>>> autoStaticArp=True )
>>>
>>>     host1 = net.addHost("h1")
>>>     host2 = net.addHost("h2")
>>>
>>>     peo1 = net.addSwitch("peo1")
>>>     peo2 = net.addSwitch("peo2")
>>>
>>>     net.addLink(peo1, peo2) # 1 | 1
>>>     net.addLink(host1, peo1)# N/A | 2
>>>     net.addLink(host2, peo2)# N/A | 2
>>>
>>>     net.start()
>>>
>>>     #PEO1 Configuration
>>>     root = Node( 'root', inNamespace=False )
>>>     root.cmd('ovs-vsctl --no-wait set bridge %s protocols=OpenFlow13'
>>> %(peo1.name))
>>>     root.cmd('ovs-ofctl -O OpenFlow13 add-flow %s
>>> "table=0,hard_timeout=0,priority=32768,in_port=2,eth_type=0x800,actions=push_mpls:0x8847,set_field:262144->mpls_label,push_mpls:0x8847,set_field:524292->mpls_label,goto_table:1"'
>>> %(peo1.name))
>>>     root.cmd('ovs-ofctl -O OpenFlow13 add-flow %s
>>> "table=1,hard_timeout=0,priority=32768,in_port=2,eth_type=0x8847,mpls_label=524292,action=output:1"'
>>> %(peo1.name))
>>>
>>>     #PEO2 Configuration
>>>     root.cmd('ovs-vsctl --no-wait set bridge %s protocols=OpenFlow13'
>>> %(peo2.name))
>>>     root.cmd('ovs-ofctl -O OpenFlow13 add-flow %s
>>> "table=0,hard_timeout=0,priority=32768,in_port=1,eth_type=0x8847,actions=goto_table=1"'
>>> %(peo2.name))
>>>     root.cmd('ovs-ofctl -O OpenFlow13 add-flow %s
>>> "table=1,hard_timeout=0,priority=32768,in_port=1,eth_type=0x8847,mpls_label=524292,action=pop_mpls:0x8847,resubmit(,1)"'
>>> %(peo2.name))
>>>     root.cmd('ovs-ofctl -O OpenFlow13 add-flow %s
>>> "table=1,hard_timeout=0,priority=32768,in_port=1,eth_type=0x8847,mpls_label=262144,mpls_bos=1,action=pop_mpls:0x800,output:2"'
>>> %(peo2.name))
>>>
>>>     CLI(net)
>>>     net.stop()
>>>     subprocess.call(["sudo", "mn", "-c"], stdout=None, stderr=None)
>>>
>>>
>>> if __name__ == '__main__':
>>>     setup()
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>> _______________________________________________
>>> discuss mailing list
>>> discuss at openvswitch.org
>>> http://openvswitch.org/mailman/listinfo/discuss
>>
>>
>
>


-- 
*******************************************************************
Stefano Salsano
Professore Associato
Dipartimento Ingegneria Elettronica
Universita' di Roma Tor Vergata
Via del Politecnico, 1 - 00133 Roma - ITALY

http://netgroup.uniroma2.it/Stefano_Salsano/

E-mail  : stefano.salsano at uniroma2.it
Cell.   : +39 320 4307310
Office  : (Tel.) +39 06 72597770  (Fax.) +39 06 72597435
*******************************************************************



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