NAME

  tst_recv_hop_limit_udp - Receiving the Hop Limit when the IPV6_RECVHOPLIMIT socket option is enabled


PURPOSE

  To check whether the hop limit be set should be used when send data on
  tcp socket, and the received hop limit can be returned correctly when
  receive data.


SYNOPSIS

  ./tst_recv_hop_limit_udp [-tooloption ...]
    -tooloption : v6api tool option


TEST PROCEDURE

  1. Create an IPv6/UDP socket
  2. Set the value of hop limit to 64
  3. Enabled the IPV6_RECVHOPLIMIT option to receive hop limit
  4. Bind the socket to address
  5. Send one message to socket itself
  6. Receive one message used recvmsg() 
  7. Check A: The hop limit option is returned
  8. Check B: The received value and length of hop limit is correct


NOTE

  None


REFERENCE

  RFC 3542
  6.3.  Specifying/Receiving the Hop Limit
    The outgoing hop limit is normally specified with either the
    IPV6_UNICAST_HOPS socket option or the IPV6_MULTICAST_HOPS socket
    option, both of which are described in [RFC-3493].  Specifying the
    hop limit as ancillary data lets the application override either the
    kernel's default or a previously specified value, for either a
    unicast destination or a multicast destination, for a single output
    operation.  Returning the received hop limit is useful for IPv6
    applications that need to verify that the received hop limit is 255
    (e.g., that the packet has not been forwarded).
    The received hop limit is returned as ancillary data by recvmsg()
    only if the application has enabled the IPV6_RECVHOPLIMIT socket
    option:
      int  on = 1;
      setsockopt(fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &on, sizeof(on));
    In the cmsghdr structure containing this ancillary data, the
    cmsg_level member will be IPPROTO_IPV6, the cmsg_type member will be
    IPV6_HOPLIMIT, and the first byte of cmsg_data[] will be the first
    byte of the integer hop limit.
    Nothing special need be done to specify the outgoing hop limit: just
    specify the control information as ancillary data for sendmsg().  As
    specified in [RFC-3493], the interpretation of the integer hop limit
    value is
      x < -1:        return an error of EINVAL
      x == -1:       use kernel default
      0 <= x <= 255: use x
      x >= 256:      return an error of EINVAL
    This API defines IPV6_HOPLIMIT as an ancillary-only option, that is,
    the option name cannot be used as a socket option.  This is because
    [RFC-3493] has more fine-grained socket options; IPV6_UNICAST_HOPS
    and IPV6_MULTICAST_HOPS.