Figure 1 – Sample network diagram.
All other traffic allowed between these hosts functioned normally; only RPC calls were failing.
2. Identifying the problem
The traffic across the networks was working without problems for most of the protocols (ICMP, SMB, DNS, HTTP, etc). Only RPC Calls were failing and the actual RPC error was exposed by using the repadmin /showreps command when run from one DC. We got the error message below:
The replication generated an error (1727): The remote procedure call failed and did not execute.
We used KB911799 (method 1) approach to understand where was failing and if ISA Server 2006 was really causing that. The tests showed that the RPC communication was failing only for communications between 64 bit platforms (Windows Server 2008 64 with Windows Server 2008 64, Windows Vista 64 with Windows Server 2008 64bit).
Looking to the network monitor trace that was taken from the DC (10.30.30.10) it was possible to see the moment of the failure when the DC from one side is trying to bind to the RPC in the other side:
TCP 3 Way Handshake for RPC:
10.30.30.10 10.40.40.16 TCP TCP:Flags=......S., SrcPort=36457, DstPort=DCE endpoint resolution(135), PayloadLen=0, Seq=102417964, Ack=0, Win=8192 (scale factor 8) = 2097152
10.40.40.16 10.30.30.10 TCP TCP:Flags=...A..S., SrcPort=DCE endpoint resolution(135), DstPort=36457, PayloadLen=0, Seq=2217804385, Ack=102417965, Win=16384 (scale factor 0) = 16384
10.30.30.10 10.40.40.16 TCP TCP:Flags=...A...., SrcPort=36457, DstPort=DCE endpoint resolution(135), PayloadLen=0, Seq=102417965, Ack=2217804386, Win=257 (scale factor 8) = 65792
RPC Bind Request for the End Point Mapper (End Point Mapper's UUID is E1AF8308-5D1F-11C9-91A4-08002B14A0FA):
10.30.30.10 10.40.40.16 MSRPC MSRPC:c/o Bind: UUID{E1AF8308-5D1F-11C9-91A4-08002B14A0FA} EPT Call=0x1 Assoc Grp=0x0 Xmit=0x16D0 Recv=0x16D0
- RPC: c/o Bind: UUID{E1AF8308-5D1F-11C9-91A4-08002B14A0FA} EPT Call=0x1 Assoc Grp=0x0 Xmit=0x16D0 Recv=0x16D0
- Bind: {E1AF8308-5D1F-11C9-91A4-08002B14A0FA} EPT
RpcVers: 5 (0x5)
RpcVersMinor: 0 (0x0)
PType: 0x0B - Bind
+ PfcFlags: 3 (0x3)
+ PackedDrep: 0x10
FragLength: 160 (0xA0)
AuthLength: 0 (0x0)
CallId: 1 (0x1)
MaxXmitFrag: 5840 (0x16D0)
MaxRecvFrag: 5840 (0x16D0)
AssocGroupId: 0 (0x0)
- PContextElem:
NContextElem: 3 (0x3)
Reserved: 0 (0x0)
Reserved2: 0 (0x0)
+ PContElem: 0x1
- PContElem: 0x1
PContId: 1 (0x1)
NTransferSyn: 1 (0x1)
Reserved: 0 (0x0)
+ AbstractSyntax: {E1AF8308-5D1F-11C9-91A4-08002B14A0FA} EPT
+ TransferSyntaxes: {71710533-BEBA-4937-8319-B5DBEF9CCC36} NDR64
+ PContElem: 0x1
RPC Bind Response:
10.40.40.16 10.30.30.10 MSRPC MSRPC:c/o Bind Ack: Call=0x1 Assoc Grp=0x87F3
- RPC: c/o Bind Ack: Call=0x1 Assoc Grp=0x87F3 Xmit=0x16D0 Recv=0x16D0
- BindAck:
RpcVers: 5 (0x5)
RpcVersMinor: 0 (0x0)
PType: 0x0C - Bind Ack
+ PfcFlags: 3 (0x3)
+ PackedDrep: 0x10
FragLength: 108 (0x6C)
AuthLength: 0 (0x0)
CallId: 1 (0x1)
MaxXmitFrag: 5840 (0x16D0)
MaxRecvFrag: 5840 (0x16D0)
AssocGroupId: 34803 (0x87F3)
+ SecAddr: 135
+ Pad2: 0x1
- PResultList:
NResults: 3 (0x3)
Reserved: 0 (0x0)
Reserved2: 0 (0x0)
- PResults: Provider rejection, Reason=Proposed transfer syntaxes not supported
Result: Provider rejection
Reason: Proposed transfer syntaxes not supported
+ TransferSyntax: {00000000-0000-0000-0000-000000000000} unknown
+ PResults: Acceptance, Reason=n/a
+ PResults: Negotiate Ack, Security Context Multiplexing Supported
The DC (10.30.30.10) sends an endpoint request for NTFRS Service UUID: f5cc59b4-4264-101a-8c59-08002b2f8426…
10.30.30.10 10.40.40.16 EPM EPM:Request: ept_map: NDR, FrsRpc {F5CC59B4-4264-101A-8C59-08002B2F8426} v1.1, RPC v5, 0.0.0.0:135 (0x87) [DCE endpoint resolution(135)]
..but the DC 10.40.40.16 closes the connection
10.40.40.16 10.30.30.10 TCP TCP:Flags=...A...F, SrcPort=DCE endpoint resolution(135), DstPort=36457, PayloadLen=0, Seq=2217804494, Ack=102418293, Win=65207 (scale factor 0) = 65207
10.30.30.10 10.40.40.16 TCP TCP:Flags=...A...., SrcPort=36457, DstPort=DCE endpoint resolution(135), PayloadLen=0, Seq=102418293, Ack=2217804495, Win=257 (scale factor 8) = 65792
10.30.30.10 10.40.40.16 TCP TCP:Flags=...A...F, SrcPort=36457, DstPort=DCE endpoint resolution(135), PayloadLen=0, Seq=102418293, Ack=2217804495, Win=257 (scale factor 8) = 65792
The key element in the above trace is the Provider Results, that appears as Provider rejection, Reason=Proposed transfer syntaxes not supported. Briefly this means that the DC 10.40.40.16 appeared to reject the bind request from DC 10.30.30.10 because the proposed transfer syntax is no supported. But this was not actually the DC 10.40.40.16 that sent that, that was ISA Server, let's understand why.
Note1: for a complete list of the meaning of each rejection reasons review Section 2 of the ISO 8823 standard.
3. RPC Filter
If you review the RPC Architecture you will notice that there is a component that belongs to the rpcrt4.dll called Marshalling Engine. This component is responsible for providing a common RPC interface between RPC clients and servers through NDR (Network Data Representation). There are two transfer syntaxes variations for the NDR:
· NDR20 – Used in 32-bit Architecture.
· NDR64 – Used in 64-bit Architecture.
When two 64bit Windows Operating System are communicating using RPC they will negotiate the marshalling engine to use. Since they both prefer NDR64, this is likely to be the format used. Natively, ISA Server 2006 RPC Filter doesn’t support NDR64; therefore the RPC Filter will reject any RPC communication which uses NDR64.
4. Resolution
To fix the problem you should install ISA Server 2006 SP1.
Author
Yuri Diogenes
Security Support Engineer – Microsoft CSS Forefront (ISA/TMG) Team
Technical Reviewers
Jim Harrison
Microsoft Forefront (ISA/TMG) Sustained Engineering Team
Doron Juster
Microsoft Forefront (ISA/TMG) Sustained Engineering Team
