[201811] [interfaces-config.sh] Flush the loopback interface addresses

[zhenggen-xu]

Flush the loopback interface before configure it

Without this, you may end up with more and more ip addresses
on loopback interface after you change the loopback ip and do config reload

Signed-off-by: Zhenggen Xu zxu@linkedin.com

- What I did
Flush the loopback interface before configure it

- How I did it
Flush the loopback interface before configure it

- How to verify it

config_db-1.json:

    "LOOPBACK_INTERFACE": {
        "Loopback0|2000::1/128": {
            "family": "IPv6",
            "scope": "global"
        },

        "Loopback0|10.10.10.1/32": {
            "family": "IPv4",
            "scope": "global"
        }
    },

config_db-2.json

    "LOOPBACK_INTERFACE": {
        "Loopback0|2000::2/128": {
            "family": "IPv6",
            "scope": "global"
        },
        "Loopback0|10.10.10.2/32": {
            "family": "IPv4",
            "scope": "global"
        }
    },

After sudo config reload config_db-1.json:

admin@sonic:~$ ip addr show lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet 10.10.10.1/32 brd 10.10.10.1 scope global lo
       valid_lft forever preferred_lft forever
    inet6 2000::1/128 scope global 
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever

Before the fix:

config reload config_db-2.json after config_db-1.json:

admin@sonic:~$ ip addr show lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet 10.10.10.1/32 brd 10.10.10.1 scope global lo
       valid_lft forever preferred_lft forever
    inet 10.10.10.2/32 brd 10.10.10.2 scope global lo
       valid_lft forever preferred_lft forever
    inet6 2000::2/128 scope global 
       valid_lft forever preferred_lft forever
    inet6 2000::1/128 scope global 
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever

After fix:

config reload config_db-2.json after config_db-1.json:

admin@sonic:~$ ip addr show lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet 10.10.10.2/32 brd 10.10.10.2 scope global lo
       valid_lft forever preferred_lft forever
    inet6 2000::2/128 scope global 
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever

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