Add script for testing BGP allow list

[wangxin]

Description of PR

Summary:
Fixes # (issue)

Add script for testing BGP allow list.

This change is dependent on the changes to tests/common/devices.py in PR #2538:

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Approach

What is the motivation for this PR?

The BGP allow list feature was introduced in SONiC. This PR is to add a script for testing the BGP allow list feature.

How did you do it?

Add a new script for testing BGP allow list. Covered scenarios:

• Ensure that constants.bgp.allow_list.default_action is "permit". No BGP allow list is configured.

  • Announce routes with and without test community '1010:1010' to the first T0 VM by exabgp.
  • Check routes on the first T0 VM. All the routes should be successfully injected.
  • Check routes on DUT. All the routes should be accepted by DUT.
  • Check routes on other T0 and T2 VMs. All the routes should be advertised by DUT. The drop_community defined in /etc/sonic/constants.yml should be added to all routes. The original community of routes should be kept.

• Ensure that constants.bgp.allow_list.default_action is "permit". BGP allow list is configured.

  • Announce routes with and without test community '1010:1010' to the first T0 VM by exabgp.
  • Check routes on the first T0 VM. All the routes should be successfully injected.
  • Check routes on DUT. All the routes should be accepted by DUT.
  • Check routes on other T0 and T2 VMs. All the routes should be advertised by DUT. The drop_community should only be added to routes not on allow list. The original community of routes should be kept.

• Ensure that constants.bgp.allow_list.default_action is "deny". No BGP allow list is configured.

  • Announce routes with and without test community '1010:1010' to the first T0 VM by exabgp.
  • Check routes on the first T0 VM. All the routes should be successfully injected.
  • Check routes on DUT. All the routes should be accepted by DUT.
  • Check routes on other T0 and T2 VMs. No routes should be advertised by DUT.

• Ensure that constants.bgp.allow_list.default_action is "deny". BGP allow list is configured.

  • Announce routes with and without test community '1010:1010' to the first T0 VM by exabgp.
  • Check routes on the first T0 VM. All the routes should be successfully injected.
  • Check routes on DUT. All the routes should be accepted by DUT.
  • Check routes on other T0 and T2 VMs. Only the routes on allow list should be advertised by DUT. No drop_community should be added to advertised routes. The original community of routes should be kept.

Relevant change: sonic-net/sonic-buildimage#5309

How did you verify/test it?

Run the test script using latest master image.

Currently some test cases can't pass because of issue: sonic-net/sonic-buildimage#6001

If add on-match next to /usr/share/sonic/templates/bgpd/templates/general/policies.conf.j2 and restart bgp service, then all the cases can pass:

route-map FROM_BGP_PEER_V6 permit 1
 on-match next
 set ipv6 next-hop prefer-global

Any platform specific information?

No

Supported testbed topology if it's a new test case?

This test only supports topology type t1.

Documentation

[pavel-shirshov]

LGTM