Re: [Patch 1/2] MdeModulePkg/Network: Add 32bit subnet mask support for IP4 PXE boot.

["Wu, Jiaxin" <jiaxin.wu@intel.com>]

Hi Siyuan,

In Ip4SendFrameToDefaultRoute(), you tried to find the default gateway IP address by using the found RtCacheEntry->Tag, I'm confused why it's the default gateway? In my understanding, tag is the cache's corresponding route entry.  Besides, why we must send the frame to "DefaultRouter", should be the instance router first, then default router? If so, I suggest to rename the function to Ip4SendFrameToRoute(). Then, the logic in the function to retrieve the gateway should be: 
{
    if (IpInstance == NULL) {
      CacheEntry = Ip4Route (IpSb->DefaultRouteTable, Head->Dst, Head->Src, IpIf->SubnetMask);
    } else {
      CacheEntry = Ip4Route (IpInstance->RouteTable, Head->Dst, Head->Src, IpIf->SubnetMask);
      if (CacheEntry == NULL) {
        CacheEntry = Ip4Route (IpSb->DefaultRouteTable, Head->Dst, Head->Src, IpIf->SubnetMask);
      }
    }

    if (CacheEntry == NULL) {
      return EFI_NOT_FOUND;
    }
    GateWay = CacheEntry->NextHop;
    Ip4FreeRouteCacheEntry (CacheEntry);
}

What do you think?

Thanks,
Jiaxin








> -----Original Message-----
> From: Fu, Siyuan
> Sent: Tuesday, August 28, 2018 9:53 AM
> To: edk2-devel@lists.01.org
> Cc: Ye, Ting <ting.ye@intel.com>; Wu, Jiaxin <jiaxin.wu@intel.com>
> Subject: [Patch 1/2] MdeModulePkg/Network: Add 32bit subnet mask
> support for IP4 PXE boot.
> 
> This patch updates IP4 stack to support 32bit subnet mask in PXE boot
> process.
> When 32bit subnet mask is used, the IP4 driver couldn't use the subnet mask
> to determine
> whether destination IP address is on-link or not, so it will always try to send
> all the
> packets to the destination IP address directly first, if failed it will continue
> to try the default gateway.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Fu Siyuan <siyuan.fu@intel.com>
> Cc: Ye Ting <ting.ye@intel.com>
> Cc: Wu Jiaxin <jiaxin.wu@intel.com>
> ---
>  MdeModulePkg/Include/Library/NetLib.h         |   5 +-
>  MdeModulePkg/Library/DxeNetLib/DxeNetLib.c    |  13 +-
>  .../Universal/Network/Ip4Dxe/Ip4Common.h      |   2 +-
>  MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.c | 117
> ++++++++++++++++--
>  MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.h |   5 +-
>  .../Universal/Network/Ip4Dxe/Ip4Impl.c        |   2 +-
>  .../Universal/Network/Ip4Dxe/Ip4Output.c      |  11 +-
>  .../Universal/Network/Ip4Dxe/Ip4Route.c       |  21 +++-
>  .../Universal/Network/Ip4Dxe/Ip4Route.h       |   5 +-
>  .../Universal/Network/Mtftp4Dxe/Mtftp4Impl.c  |   6 +-
>  10 files changed, 154 insertions(+), 33 deletions(-)
> 
> diff --git a/MdeModulePkg/Include/Library/NetLib.h
> b/MdeModulePkg/Include/Library/NetLib.h
> index ef7bc429c1..b7ef99c7b5 100644
> --- a/MdeModulePkg/Include/Library/NetLib.h
> +++ b/MdeModulePkg/Include/Library/NetLib.h
> @@ -422,8 +422,9 @@ NetGetIpClass (
> 
>    If all bits of the host address of IP are 0 or 1, IP is also not a valid unicast
> address,
>    except when the originator is one of the endpoints of a point-to-point link
> with a 31-bit
> -  mask (RFC3021).
> -
> +  mask (RFC3021), or a 32bit NetMask (all 0xFF) is used for special network
> environment (e.g.
> +  PPP link).
> +
>    @param[in]  Ip                    The IP to check against.
>    @param[in]  NetMask               The mask of the IP.
> 
> diff --git a/MdeModulePkg/Library/DxeNetLib/DxeNetLib.c
> b/MdeModulePkg/Library/DxeNetLib/DxeNetLib.c
> index bf8f5523e6..63f4724062 100644
> --- a/MdeModulePkg/Library/DxeNetLib/DxeNetLib.c
> +++ b/MdeModulePkg/Library/DxeNetLib/DxeNetLib.c
> @@ -654,8 +654,9 @@ NetGetIpClass (
> 
>    If all bits of the host address of IP are 0 or 1, IP is also not a valid unicast
> address,
>    except when the originator is one of the endpoints of a point-to-point link
> with a 31-bit
> -  mask (RFC3021).
> -
> +  mask (RFC3021), or a 32bit NetMask (all 0xFF) is used for special network
> environment (e.g.
> +  PPP link).
> +
>    @param[in]  Ip                    The IP to check against.
>    @param[in]  NetMask               The mask of the IP.
> 
> @@ -669,18 +670,20 @@ NetIp4IsUnicast (
>    IN IP4_ADDR               NetMask
>    )
>  {
> +  INTN   MaskLength;
> +
>    ASSERT (NetMask != 0);
> 
>    if (Ip == 0 || IP4_IS_LOCAL_BROADCAST (Ip)) {
>      return FALSE;
>    }
> 
> -  if (NetGetMaskLength (NetMask) != 31) {
> +  MaskLength = NetGetMaskLength (NetMask);
> +  ASSERT ((MaskLength >= 0) && (MaskLength <= IP4_MASK_NUM));
> +  if (MaskLength < 31) {
>      if (((Ip &~NetMask) == ~NetMask) || ((Ip &~NetMask) == 0)) {
>        return FALSE;
>      }
> -  } else {
> -    return TRUE;
>    }
> 
>    return TRUE;
> diff --git a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Common.h
> b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Common.h
> index e0fffc9d0d..994a81f4de 100644
> --- a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Common.h
> +++ b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Common.h
> @@ -55,7 +55,7 @@ typedef struct _IP4_SERVICE    IP4_SERVICE;
>  /// Compose the fragment field to be used in the IP4 header.
>  ///
>  #define IP4_HEAD_FRAGMENT_FIELD(Df, Mf, Offset) \
> -    ((UINT16)(((Df) ? 0x4000 : 0) | ((Mf) ? 0x2000 : 0) | (((Offset) >> 3) &
> 0x1fff)))
> +    ((UINT16)(((Df) ? IP4_HEAD_DF_MASK : 0) | ((Mf) ?
> IP4_HEAD_MF_MASK : 0) | (((Offset) >> 3) & IP4_HEAD_OFFSET_MASK)))
> 
>  #define IP4_LAST_FRAGMENT(FragmentField)  \
>            (((FragmentField) & IP4_HEAD_MF_MASK) == 0)
> diff --git a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.c
> b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.c
> index 6e0e3290c7..b0172283b7 100644
> --- a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.c
> +++ b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.c
> @@ -138,6 +138,7 @@ Ip4CancelFrameArp (
>    @param[in]  CallBack          Call back function to execute if transmission
>                                  finished.
>    @param[in]  Context           Opaque parameter to the call back.
> +  @param[in]  IpSb              The pointer to the IP4 service binding instance.
> 
>    @retval   Token               The wrapped token if succeed
>    @retval   NULL                The wrapped token if NULL
> @@ -149,7 +150,8 @@ Ip4WrapLinkTxToken (
>    IN IP4_PROTOCOL           *IpInstance     OPTIONAL,
>    IN NET_BUF                *Packet,
>    IN IP4_FRAME_CALLBACK     CallBack,
> -  IN VOID                   *Context
> +  IN VOID                   *Context,
> +  IN IP4_SERVICE            *IpSb
>    )
>  {
>    EFI_MANAGED_NETWORK_COMPLETION_TOKEN  *MnpToken;
> @@ -170,6 +172,7 @@ Ip4WrapLinkTxToken (
> 
>    Token->Interface  = Interface;
>    Token->IpInstance = IpInstance;
> +  Token->IpSb       = IpSb;
>    Token->CallBack   = CallBack;
>    Token->Packet     = Packet;
>    Token->Context    = Context;
> @@ -792,6 +795,86 @@ Ip4FreeInterface (
>    return EFI_SUCCESS;
>  }
> 
> +/**
> +  This function tries to send all the queued frames in ArpQue to the default
> gateway if
> +  the ARP resolve for direct destination address is failed when using /32
> subnet mask.
> +
> +  @param[in]   ArpQue           The ARP queue of a failed request.
> +
> +  @retval EFI_SUCCESS           All the queued frames have been send to the
> default route.
> +  @retval Others                Failed to send the queued frames.
> +
> +**/
> +EFI_STATUS
> +Ip4SendFrameToDefaultRoute (
> +  IN  IP4_ARP_QUE               *ArpQue
> +  )
> +{
> +  LIST_ENTRY                *Entry;
> +  LIST_ENTRY                *Next;
> +  IP4_ROUTE_CACHE_ENTRY     *RtCacheEntry;
> +  IP4_LINK_TX_TOKEN         *Token;
> +  IP4_ADDR                  Gateway;
> +  EFI_STATUS                Status;
> +  IP4_ROUTE_ENTRY           *DefaultRoute;
> +
> +  //
> +  // ARP resolve failed when using /32 subnet mask.
> +  //
> +  NET_LIST_FOR_EACH_SAFE (Entry, Next, &ArpQue->Frames) {
> +    RemoveEntryList (Entry);
> +    Token = NET_LIST_USER_STRUCT (Entry, IP4_LINK_TX_TOKEN, Link);
> +    ASSERT (Token->Interface->SubnetMask == IP4_ALLONE_ADDRESS);
> +    //
> +    // Find the default gateway IP address. The default route was saved to
> the RtCacheEntry->Tag in Ip4Route().
> +    //
> +    RtCacheEntry = NULL;
> +    if (Token->IpInstance != NULL) {
> +      RtCacheEntry = Ip4FindRouteCache (Token->IpInstance->RouteTable,
> NTOHL (ArpQue->Ip), Token->Interface->Ip);
> +    }
> +    if (RtCacheEntry == NULL) {
> +      RtCacheEntry = Ip4FindRouteCache (Token->IpSb->DefaultRouteTable,
> NTOHL (ArpQue->Ip), Token->Interface->Ip);
> +    }
> +    if (RtCacheEntry == NULL) {
> +      Status= EFI_NO_MAPPING;
> +      goto ON_ERROR;
> +    }
> +    DefaultRoute = (IP4_ROUTE_ENTRY*)RtCacheEntry->Tag;
> +    if (DefaultRoute == NULL) {
> +      Status= EFI_NO_MAPPING;
> +      goto ON_ERROR;
> +    }
> +    //
> +    // Try to send the frame to the default route.
> +    //
> +    Gateway = DefaultRoute->NextHop;
> +    if (ArpQue->Ip == Gateway) {
> +      //
> +      // ARP resolve for the default route is failed, return error to caller.
> +      //
> +      Status= EFI_NO_MAPPING;
> +      goto ON_ERROR;
> +    }
> +    RtCacheEntry->NextHop = Gateway;
> +    Status = Ip4SendFrame (Token->Interface,Token->IpInstance,Token-
> >Packet,Gateway,Token->CallBack,Token->Context,Token->IpSb);
> +    if (EFI_ERROR (Status)) {
> +      Status= EFI_NO_MAPPING;
> +      goto ON_ERROR;
> +    }
> +    Ip4FreeRouteCacheEntry (RtCacheEntry);
> +  }
> +
> +  return EFI_SUCCESS;
> +
> +ON_ERROR:
> +  if (RtCacheEntry != NULL) {
> +    Ip4FreeRouteCacheEntry (RtCacheEntry);
> +  }
> +  Token->CallBack (Token->IpInstance, Token->Packet, Status, 0, Token-
> >Context);
> +  Ip4FreeLinkTxToken (Token);
> +  return Status;
> +}
> +
> 
>  /**
>    Callback function when ARP request are finished. It will cancelled
> @@ -814,6 +897,7 @@ Ip4OnArpResolvedDpc (
>    IP4_INTERFACE             *Interface;
>    IP4_LINK_TX_TOKEN         *Token;
>    EFI_STATUS                Status;
> +  EFI_STATUS                IoStatus;
> 
>    ArpQue = (IP4_ARP_QUE *) Context;
>    NET_CHECK_SIGNATURE (ArpQue, IP4_FRAME_ARP_SIGNATURE);
> @@ -821,14 +905,23 @@ Ip4OnArpResolvedDpc (
>    RemoveEntryList (&ArpQue->Link);
> 
>    //
> -  // ARP resolve failed for some reason. Release all the frame
> -  // and ARP queue itself. Ip4FreeArpQue will call the frame's
> -  // owner back.
> +  // ARP resolve failed for some reason.
>    //
>    if (NET_MAC_EQUAL (&ArpQue->Mac, &mZeroMacAddress, ArpQue-
> >Interface->HwaddrLen)) {
> -    Ip4FreeArpQue (ArpQue, EFI_NO_MAPPING);
> -
> -    return ;
> +    if (ArpQue->Interface->SubnetMask != IP4_ALLONE_ADDRESS) {
> +      //
> +      // Release all the frame and ARP queue itself. Ip4FreeArpQue will call the
> frame's
> +      // owner back.
> +      //
> +      IoStatus = EFI_NO_MAPPING;
> +    } else {
> +      //
> +      // ARP resolve failed when using 32bit subnet mask, try to send the
> packets to the
> +      // default route.
> +      //
> +      IoStatus = Ip4SendFrameToDefaultRoute (ArpQue);
> +    }
> +    goto ON_EXIT;
>    }
> 
>    //
> @@ -836,6 +929,7 @@ Ip4OnArpResolvedDpc (
>    // queue. It isn't necessary for us to cache the ARP binding because
>    // we always check the ARP cache first before transmit.
>    //
> +  IoStatus = EFI_SUCCESS;
>    Interface = ArpQue->Interface;
> 
>    NET_LIST_FOR_EACH_SAFE (Entry, Next, &ArpQue->Frames) {
> @@ -863,7 +957,8 @@ Ip4OnArpResolvedDpc (
>      }
>    }
> 
> -  Ip4FreeArpQue (ArpQue, EFI_SUCCESS);
> +ON_EXIT:
> +  Ip4FreeArpQue (ArpQue, IoStatus);
>  }
> 
>  /**
> @@ -957,6 +1052,7 @@ Ip4OnFrameSent (
>                                  to.
>    @param[in]  CallBack          Function to call back when transmit finished.
>    @param[in]  Context           Opaque parameter to the call back.
> +  @param[in]  IpSb              The pointer to the IP4 service binding instance.
> 
>    @retval EFI_OUT_OF_RESOURCES  Failed to allocate resource to send the
> frame
>    @retval EFI_NO_MAPPING        Can't resolve the MAC for the nexthop
> @@ -971,7 +1067,8 @@ Ip4SendFrame (
>    IN  NET_BUF               *Packet,
>    IN  IP4_ADDR              NextHop,
>    IN  IP4_FRAME_CALLBACK    CallBack,
> -  IN  VOID                  *Context
> +  IN  VOID                  *Context,
> +  IN IP4_SERVICE            *IpSb
>    )
>  {
>    IP4_LINK_TX_TOKEN         *Token;
> @@ -982,7 +1079,7 @@ Ip4SendFrame (
> 
>    ASSERT (Interface->Configured);
> 
> -  Token = Ip4WrapLinkTxToken (Interface, IpInstance, Packet, CallBack,
> Context);
> +  Token = Ip4WrapLinkTxToken (Interface, IpInstance, Packet, CallBack,
> Context, IpSb);
> 
>    if (Token == NULL) {
>      return EFI_OUT_OF_RESOURCES;
> diff --git a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.h
> b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.h
> index 909837131e..36e4ab3f7a 100644
> --- a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.h
> +++ b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4If.h
> @@ -79,6 +79,7 @@ typedef struct {
>    LIST_ENTRY                            Link;
> 
>    IP4_INTERFACE                         *Interface;
> +  IP4_SERVICE                           *IpSb;
> 
>    IP4_PROTOCOL                          *IpInstance;
>    IP4_FRAME_CALLBACK                    CallBack;
> @@ -262,6 +263,7 @@ Ip4FreeInterface (
>                                  to.
>    @param[in]  CallBack          Function to call back when transmit finished.
>    @param[in]  Context           Opaque parameter to the call back.
> +  @param[in]  IpSb              The pointer to the IP4 service binding instance.
> 
>    @retval EFI_OUT_OF_RESOURCES  Failed to allocate resource to send the
> frame
>    @retval EFI_NO_MAPPING        Can't resolve the MAC for the nexthop
> @@ -276,7 +278,8 @@ Ip4SendFrame (
>    IN  NET_BUF               *Packet,
>    IN  IP4_ADDR              NextHop,
>    IN  IP4_FRAME_CALLBACK    CallBack,
> -  IN  VOID                  *Context
> +  IN  VOID                  *Context,
> +  IN IP4_SERVICE            *IpSb
>    );
> 
>  /**
> diff --git a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Impl.c
> b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Impl.c
> index 6a26143e30..7c27db6753 100644
> --- a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Impl.c
> +++ b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Impl.c
> @@ -1259,7 +1259,7 @@ EfiIp4Routes (
>    // the gateway address must be a unicast on the connected network if not
> zero.
>    //
>    if ((Nexthop != IP4_ALLZERO_ADDRESS) &&
> -      (!IP4_NET_EQUAL (Nexthop, IpIf->Ip, IpIf->SubnetMask) ||
> +      ((IpIf->SubnetMask != IP4_ALLONE_ADDRESS && !IP4_NET_EQUAL
> (Nexthop, IpIf->Ip, IpIf->SubnetMask)) ||
>          IP4_IS_BROADCAST (Ip4GetNetCast (Nexthop, IpIf)))) {
> 
>      Status = EFI_INVALID_PARAMETER;
> diff --git a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Output.c
> b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Output.c
> index 1716f43576..bbbcf36eff 100644
> --- a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Output.c
> +++ b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Output.c
> @@ -309,15 +309,15 @@ Ip4Output (
>      // Route the packet unless overrided, that is, GateWay isn't zero.
>      //
>      if (IpInstance == NULL) {
> -      CacheEntry = Ip4Route (IpSb->DefaultRouteTable, Head->Dst, Head-
> >Src);
> +      CacheEntry = Ip4Route (IpSb->DefaultRouteTable, Head->Dst, Head->Src,
> IpIf->SubnetMask);
>      } else {
> -      CacheEntry = Ip4Route (IpInstance->RouteTable, Head->Dst, Head->Src);
> +      CacheEntry = Ip4Route (IpInstance->RouteTable, Head->Dst, Head->Src,
> IpIf->SubnetMask);
>        //
>        // If failed to route the packet by using the instance's route table,
>        // try to use the default route table.
>        //
>        if (CacheEntry == NULL) {
> -        CacheEntry = Ip4Route (IpSb->DefaultRouteTable, Head->Dst, Head-
> >Src);
> +        CacheEntry = Ip4Route (IpSb->DefaultRouteTable, Head->Dst, Head-
> >Src, IpIf->SubnetMask);
>        }
>      }
> 
> @@ -386,7 +386,8 @@ Ip4Output (
>                   Fragment,
>                   GateWay,
>                   Ip4SysPacketSent,
> -                 Packet
> +                 Packet,
> +                 IpSb
>                   );
> 
>        if (EFI_ERROR (Status)) {
> @@ -429,7 +430,7 @@ Ip4Output (
>    //    upper layer's packets.
>    //
>    Ip4PrependHead (Packet, Head, Option, OptLen);
> -  Status = Ip4SendFrame (IpIf, IpInstance, Packet, GateWay, Callback,
> Context);
> +  Status = Ip4SendFrame (IpIf, IpInstance, Packet, GateWay, Callback,
> Context, IpSb);
> 
>    if (EFI_ERROR (Status)) {
>      goto ON_ERROR;
> diff --git a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Route.c
> b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Route.c
> index d240d5343a..e648dee908 100644
> --- a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Route.c
> +++ b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Route.c
> @@ -494,6 +494,8 @@ Ip4FindRouteEntry (
>    @param[in]  RtTable               The route table to search from
>    @param[in]  Dest                  The destination address to search for
>    @param[in]  Src                   The source address to search for
> +  @param[in]  SubnetMask            The subnet mask of the Src address, this
> field is
> +                                    used to check if the station is using /32 subnet.
> 
>    @return NULL if failed to route packet, otherwise a route cache
>            entry that can be used to route packet.
> @@ -503,7 +505,8 @@ IP4_ROUTE_CACHE_ENTRY *
>  Ip4Route (
>    IN IP4_ROUTE_TABLE        *RtTable,
>    IN IP4_ADDR               Dest,
> -  IN IP4_ADDR               Src
> +  IN IP4_ADDR               Src,
> +  IN IP4_ADDR               SubnetMask
>    )
>  {
>    LIST_ENTRY                *Head;
> @@ -534,7 +537,10 @@ Ip4Route (
>    //
>    RtEntry = Ip4FindRouteEntry (RtTable, Dest);
> 
> -  if (RtEntry == NULL) {
> +  //
> +  // We will always try to use the direct destination address when /32 subnet
> mask is used.
> +  //
> +  if (RtEntry == NULL && SubnetMask != IP4_ALLONE_ADDRESS) {
>      return NULL;
>    }
> 
> @@ -544,16 +550,23 @@ Ip4Route (
>    // network. Otherwise, it is an indirect route, the packet will be
>    // sent to the next hop router.
>    //
> -  if ((RtEntry->Flag & IP4_DIRECT_ROUTE) != 0) {
> +  // When using /32 subnet mask, the packet will always be sent to the
> direct
> +  // destination first, if we can't find a matching route cache.
> +  //
> +  if (SubnetMask == IP4_ALLONE_ADDRESS || ((RtEntry->Flag &
> IP4_DIRECT_ROUTE) != 0)) {
>      NextHop = Dest;
>    } else {
>      NextHop = RtEntry->NextHop;
>    }
> 
> -  Ip4FreeRouteEntry (RtEntry);
> +  if (RtEntry != NULL) {
> +    Ip4FreeRouteEntry (RtEntry);
> +  }
> 
>    //
>    // Create a route cache entry, and tag it as spawned from this route entry
> +  // For /32 subnet mask, the default route in RtEntry will be used if failed
> +  // to send the packet to driect destination address.
>    //
>    RtCacheEntry = Ip4CreateRouteCacheEntry (Dest, Src, NextHop, (UINTN)
> RtEntry);
> 
> diff --git a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Route.h
> b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Route.h
> index 6269f4ceda..99b9cfbbac 100644
> --- a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Route.h
> +++ b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Route.h
> @@ -194,6 +194,8 @@ Ip4FreeRouteCacheEntry (
>    @param[in]  RtTable               The route table to search from
>    @param[in]  Dest                  The destination address to search for
>    @param[in]  Src                   The source address to search for
> +  @param[in]  SubnetMask            The subnet mask of the Src address, this
> field is
> +                                    used to check if the station is using /32 subnet.
> 
>    @return NULL if failed to route packet, otherwise a route cache
>            entry that can be used to route packet.
> @@ -203,7 +205,8 @@ IP4_ROUTE_CACHE_ENTRY *
>  Ip4Route (
>    IN IP4_ROUTE_TABLE        *RtTable,
>    IN IP4_ADDR               Dest,
> -  IN IP4_ADDR               Src
> +  IN IP4_ADDR               Src,
> +  IN IP4_ADDR               SubnetMask
>    );
> 
>  /**
> diff --git a/MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c
> b/MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c
> index d5a1a8c303..03903640b8 100644
> --- a/MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c
> +++ b/MdeModulePkg/Universal/Network/Mtftp4Dxe/Mtftp4Impl.c
> @@ -509,8 +509,9 @@ Mtftp4Start (
>      goto ON_ERROR;
>    }
> 
> +  gBS->RestoreTPL(OldTpl);
> +
>    if (Token->Event != NULL) {
> -    gBS->RestoreTPL (OldTpl);
>      return EFI_SUCCESS;
>    }
> 
> @@ -522,7 +523,6 @@ Mtftp4Start (
>      This->Poll (This);
>    }
> 
> -  gBS->RestoreTPL (OldTpl);
>    return Token->Status;
> 
>  ON_ERROR:
> @@ -682,7 +682,7 @@ EfiMtftp4Configure (
>      }
> 
>      if ((Gateway != 0) &&
> -        (!IP4_NET_EQUAL (Gateway, Ip, Netmask) || (Netmask != 0
> && !NetIp4IsUnicast (Gateway, Netmask)))) {
> +        ((Netmask != 0xFFFFFFFF && !IP4_NET_EQUAL (Gateway, Ip, Netmask))
> || (Netmask != 0 && !NetIp4IsUnicast (Gateway, Netmask)))) {
> 
>        return EFI_INVALID_PARAMETER;
>      }
> --
> 2.18.0.windows.1