[srslte-users] LTE SPGW /30 ip addressing woes

[Roderick Groesbeek]

Hi list,

I have a setup like
EPC&ENB <----> 4x Sierra Wireless 7455 modem

We retrieve the 4x IP's on UE side via "dhclient".


But I experience the following (I think) DHCLIENT behavior:

  *   /30 subnet rollouts
  *   /29 subnet rollouts

My guess is that dhclient configures a /30 and allocates 1 Gateway, and 1 Client IP address, where
the SPGW just allocates 1 ip to the UE, never minding the Gateway IP that dhclient also provisions.
(For connection #1 the Gateway IP, can be given out as a client IP on Connection #2)

Resume:
=======
So if you rollout multiple LTE connections on 1 host, you could get routing and subnetting problems.

  *   Ip conflicts
  *   Subnetting translation problems


What would be the best rollout/solution/fix for this?
Maybe rollout only static ip addressing and then modulo 2?





I see the code for generating a new IP is pretty straightforward, and do not expect a bug there..

in_addr_t spgw::gtpc::get_new_ue_ipv4(uint64_t imsi)
{
  struct in_addr ue_addr;

  std::map<uint64_t, struct in_addr>::const_iterator iter = m_imsi_to_ip.find(imsi);
  if (iter != m_imsi_to_ip.end()) {
    ue_addr = iter->second;
    m_gtpc_log->info("SPGW: get_new_ue_ipv4 static ip addr %s\n", inet_ntoa(ue_addr));
  } else {
    if (m_ue_ip_addr_pool.empty()) {
      m_gtpc_log->error("SPGW: ue address pool is empty\n");
      ue_addr.s_addr = 0;
    } else {
      ue_addr.s_addr = *m_ue_ip_addr_pool.begin();
      m_ue_ip_addr_pool.erase(ue_addr.s_addr);
      m_gtpc_log->info("SPGW: get_new_ue_ipv4 pool ip addr %s\n", inet_ntoa(ue_addr));
    }
  }
  return ue_addr.s_addr;
}

What would be the best setup to avoid this subnet/ip conflicting?
Is there a way to keep it dynamic but more controlling on the ENB side?


GR,
RG
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