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[Contrail] Understanding Sinfo field in a flow entry

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Article ID: KB33638 KB Last Updated: 04 Jan 2019Version: 1.0
Summary:

Sinfo field in a flow entry is used to track the source of a packet. For a packet from fabric, the source of tunnel will be put into Sinfo field. For a packet sent from VM, vif index is used as Sinfo. 

Solution:

For instance, VM 111.111.111.3 is on compute node 172.18.102.106, and VM 111.111.111.4 is on compute node 172.18.101.105. While pinging 111.111.111.3 from 111.111.111.4, on compute node 172.18.101.105, we can see the following flow entry:

root@comp105:~# flow --match 111.111.111.4
Flow table(size 80609280, entries 629760)
Entries: Created 18774 Added 18774 Deleted 37506 Changed 37506 Processed 18774 Used Overflow entries 0
(Created Flows/CPU: 10 1249 10 868 4 926 6 619 10 613 9 441 10 7044 6 1540 4 2867 4 875 2 1100 14 543)(oflows 0)

Action:F=Forward, D=Drop N=NAT(S=SNAT, D=DNAT, Ps=SPAT, Pd=DPAT, L=Link Local Port)
 Other:K(nh)=Key_Nexthop, S(nh)=RPF_Nexthop
 Flags:E=Evicted, Ec=Evict Candidate, N=New Flow, M=Modified Dm=Delete Marked
TCP(r=reverse):S=SYN, F=FIN, R=RST, C=HalfClose, E=Established, D=Dead

Listing flows matching ([111.111.111.4]:*)

    Index                Source:Port/Destination:Port                      Proto(V)
-----------------------------------------------------------------------------------
    17000<=>484992       111.111.111.4:26626                                 1 (9)
                         111.111.111.3:0    
(Gen: 19, K(nh):61, Action:F, Flags:, QOS:-1, S(nh):61,  Stats:168798/16542204, 
 SPort 61046, TTL 0, Sinfo 3.0.0.0)

   484992<=>17000        111.111.111.3:26626                                 1 (9)
                         111.111.111.4:0    
(Gen: 1, K(nh):61, Action:F, Flags:, QOS:-1, S(nh):44,  Stats:168798/16542204, 
 SPort 59731, TTL 0, Sinfo 172.18.102.106)


Here, for the first entry, Sinfo 3.0.0.0 means the source of this flow is from VMI with vif index 3:

root@comp105:~# 
root@comp105:~# nh --get 61
Id:61         Type:Encap          Fmly: AF_INET  Rid:0  Ref_cnt:4          Vrf:9
              Flags:Valid, Policy, 
              EncapFmly:0806 Oif:3 Len:14
              Encap Data: 02 e2 c8 da df 5f 00 00 5e 00 01 00 08 00 

root@comp105:~# vif --get 3
Vrouter Interface Table

Flags: P=Policy, X=Cross Connect, S=Service Chain, Mr=Receive Mirror
       Mt=Transmit Mirror, Tc=Transmit Checksum Offload, L3=Layer 3, L2=Layer 2
       D=DHCP, Vp=Vhost Physical, Pr=Promiscuous, Vnt=Native Vlan Tagged
       Mnp=No MAC Proxy, Dpdk=DPDK PMD Interface, Rfl=Receive Filtering Offload, Mon=Interface is Monitored
       Uuf=Unknown Unicast Flood, Vof=VLAN insert/strip offload, Df=Drop New Flows, Proxy=MAC Requests Proxied Always
       Mn=Mirror without Vlan Tag

vif0/3      OS: tape2c8dadf-5f
            Type:Virtual HWaddr:00:00:5e:00:01:00 IPaddr:111.111.111.4
            Vrf:9 Flags:PL3L2D QOS:-1 Ref:5
            RX packets:190982  bytes:17480316 errors:0
            TX packets:190990  bytes:17480652 errors:0
            Drops:2


While for the other flow, Sinfo 172.18.102.106 is straight forward, pointing to the source of tunnel:

root@comp105:~# nh --get 44
Id:44         Type:Tunnel         Fmly: AF_INET  Rid:0  Ref_cnt:54         Vrf:0
              Flags:Valid, MPLSoUDP, 
              Oif:0 Len:14 Flags Valid, MPLSoUDP,  Data:f0 1c 2d 41 90 00 00 50 56 85 65 dd 08 00 
              Vrf:0  Sip:172.18.101.105  Dip:172.18.102.106 
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