[ovs-discuss] [ovn] TCP/UDP traffic dropped between IP addresses defined in allowed address pairs when remote security group is used

[Krzysztof Klimonda]

Hi,

After upgrading to OVN 20.12.0 snapshot d8bc0377c I've noticed a problem in communication between VMs that use allowed address pairs and remote group id in security groups. I believe it has worked properly with OVN 20.06.2 release (although I have no way of verifying it right now).

Given the following scenario:

- 2 VMs with IP addresses: vm-a with IP addresses 10.0.0.10 and 172.16.0.10 and vm-b with IP addresses 10.0.0.11 and 172.16.0.11 where 10.0.0.0/8 addresses are set on ports, and 172.16.0.0/16 addresses are set in allowed-address for on ports
- There is single security group attached to both ports allowing for ingress tcp traffic coming from the same security group (remote-group)
- There is a TCP service listening on 10.0.0.10 on port 8000

When I try accessing service from vm-b using 10.0.0.10 address, ovn forwards traffic properly. However, when I try accessing same service via 172.16.0.10 traffic is dropped.

When I trace packets between VMs using ovn-trace, for first scenario the last step is:

----8<----8<----
ct_next(ct_state=est|trk /* default (use --ct to customize) */)
---------------------------------------------------------------
 4. ls_out_acl_hint (ovn-northd.c:5292): !ct.new && ct.est && !ct.rpl && ct_label.blocked == 0, priority 4, uuid ab5a233e
    reg0[8] = 1;
    reg0[10] = 1;
    next;
 5. ls_out_acl (ovn-northd.c:5498): reg0[8] == 1 && (outport == @pg_ed081ef3_754a_492f_80b2_fb73cd2dceed && ip4 && ip4.src == $pg_ed081ef3_754a_492f_80b2_fb73cd2dceed_ip4 && tcp), priority 2002, uuid d92706d4
    next;
 9. ls_out_port_sec_ip (ovn-northd.c:4525): outport == "864929" && eth.dst == fa:16:3e:bc:20:10 && ip4.dst == {255.255.255.255, 224.0.0.0/4, 10.0.0.10, 172.16.0.0/16}, priority 90, uuid ff3390b1
    next;
10. ls_out_port_sec_l2 (ovn-northd.c:4929): outport == "864929" && eth.dst == {fa:16:3e:bc:20:10}, priority 50, uuid af91c05c
    output;
    /* output to "864929", type "" */
----8<----8<----

However, when I use 172.16.0.0/24 addresses, the last step changes to:

----8<----8<----
ct_next(ct_state=est|trk /* default (use --ct to customize) */)
---------------------------------------------------------------
 4. ls_out_acl_hint (ovn-northd.c:5292): !ct.new && ct.est && !ct.rpl && ct_label.blocked == 0, priority 4, uuid ab5a233e
    reg0[8] = 1;
    reg0[10] = 1;
    next;
 5. ls_out_acl (ovn-northd.c:5553): reg0[10] == 1 && (outport == @neutron_pg_drop && ip), priority 2001, uuid e36c0840
    ct_commit { ct_label.blocked = 1; };
----8<----8<----

Further notes:

- ICMP traffic between 172.16.0.0/24 addresses is forwarded correctly, with last step of ovn-trace being:

----8<----8<----
ct_next(ct_state=est|trk /* default (use --ct to customize) */)
---------------------------------------------------------------
 4. ls_out_acl_hint (ovn-northd.c:5292): !ct.new && ct.est && !ct.rpl && ct_label.blocked == 0, priority 4, uuid ab5a233e
    reg0[8] = 1;
    reg0[10] = 1;
    next;
 5. ls_out_acl (ovn-northd.c:5498): reg0[8] == 1 && (outport == @pg_ed081ef3_754a_492f_80b2_fb73cd2dceed && ip4 && ip4.src == 0.0.0.0/0 && icmp4), priority 2002, uuid cd1705d8
    next;
 9. ls_out_port_sec_ip (ovn-northd.c:4525): outport == "864929" && eth.dst == fa:16:3e:bc:20:10 && ip4.dst == {255.255.255.255, 224.0.0.0/4, 10.0.0.10, 172.16.0.0/16}, priority 90, uuid ff3390b1
    next;
10. ls_out_port_sec_l2 (ovn-northd.c:4929): outport == "864929" && eth.dst == {fa:16:3e:bc:20:10}, priority 50, uuid af91c05c
    output;
    /* output to "864929", type "" */
----8<----8<----

- If I replace security group rule, changing remote group to remote ip, traffic is forwarded correctly and last step in ovn-trace is:

----8<----8<----
ct_next(ct_state=est|trk /* default (use --ct to customize) */)
---------------------------------------------------------------
 4. ls_out_acl_hint (ovn-northd.c:5292): !ct.new && ct.est && !ct.rpl && ct_label.blocked == 0, priority 4, uuid ab5a233e
    reg0[8] = 1;
    reg0[10] = 1;
    next;
 5. ls_out_acl (ovn-northd.c:5498): reg0[8] == 1 && (outport == @pg_ed081ef3_754a_492f_80b2_fb73cd2dceed && ip4 && ip4.src == 172.16.0.0/24 && tcp), priority 2002, uuid a0871ca2
    next;
 9. ls_out_port_sec_ip (ovn-northd.c:4525): outport == "864929" && eth.dst == fa:16:3e:bc:20:10 && ip4.dst == {255.255.255.255, 224.0.0.0/4, 10.0.0.10, 172.16.0.0/16}, priority 90, uuid ff3390b1
    next;
10. ls_out_port_sec_l2 (ovn-northd.c:4929): outport == "864929" && eth.dst == {fa:16:3e:bc:20:10}, priority 50, uuid af91c05c
    output;
    /* output to "864929", type "" */
----8<----8<----

-- 
  Krzysztof Klimonda
  kklimonda at syntaxhighlighted.com