def get_arp_table(self, vrf="<STR_LIT>"):
raise NotImplementedError<EOL>
Returns a list of dictionaries having the following set of keys:
    * interface (string)
    * mac (string)
    * ip (string)
    * age (float)

'vrf' of null-string will default to all VRFs. Specific 'vrf' will return the ARP table
entries for that VRFs (including potentially 'default' or 'global').

In all cases the same data structure is returned and no reference to the VRF that was used
is included in the output.

Example::

    [
        {
            'interface' : 'MgmtEth0/RSP0/CPU0/0',
            'mac'       : '5C:5E:AB:DA:3C:F0',
            'ip'        : '172.17.17.1',
            'age'       : 1454496274.84
        },
        {
            'interface' : 'MgmtEth0/RSP0/CPU0/0',
            'mac'       : '5C:5E:AB:DA:3C:FF',
            'ip'        : '172.17.17.2',
            'age'       : 1435641582.49
        }
    ]