docs: def add_router_interface(self, context, router_info):
          """Adds an interface to a router created on Arista HW router.
  
          This deals with both IPv6 and IPv4 configurations.
          """
          if router_info:
              self._select_dicts(router_info['ip_version'])
              cidr = router_info['cidr']
              subnet_mask = cidr.split('/')[1]
              router_name = self._arista_router_name(router_info['id'],
                                                     router_info['name'])
              if self._mlag_configured:
                  # For MLAG, we send a specific IP address as opposed to cidr
                  # For now, we are using x.x.x.253 and x.x.x.254 as virtual IP
                  mlag_peer_failed = False
                  for i, server in enumerate(self._servers):
                      # Get appropriate virtual IP address for this router
                      router_ip = self._get_router_ip(cidr, i,
                                                      router_info['ip_version'])
                      try:
                          self.add_interface_to_router(router_info['seg_id'],
                                                       router_name,
                                                       router_info['gip'],
                                                       router_ip, subnet_mask,
                                                       server)
                          mlag_peer_failed = False
                      except Exception:
                          if not mlag_peer_failed:
                              mlag_peer_failed = True
                          else:
                              msg = (_('Failed to add interface to router '
                                       '%s on EOS') % router_name)
                              LOG.exception(msg)
                              raise arista_exc.AristaServicePluginRpcError(
                                  msg=msg)
  
              else:
                  for s in self._servers:
                      self.add_interface_to_router(router_info['seg_id'],
                                                   router_name,
                                                   router_info['gip'],
                                                   None, subnet_mask, s)