INTERNET DRAFT V. Kashyap
<draft-kashyap-ipoib-connected-mode-01.txt> IBM
Expiration Date: March 2004 September 2003
IP over InfiniBand: Connected Mode
Status of this memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC 2026.
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Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
The InfiniBand Architecture(IBA) defines a high speed, channel
based interconnect between systems and devices. IBA provides
multiple modes of transport services with differing
characteristics. This document describes IP over IBA's Connected
transport modes.
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Table of Contents
1.0 Introduction
2.0 IPoIB-connected mode
2.1 Outline of Address Resolution
2.2 Outline of Connection Setup
3.0 Address Resolution
4.0 Connection setup
4.1 Service ID
4.2 MTU
5.0 IP Encapsulation
6.0 Security Considerations
7.0 References
1.0 Introduction
IBA defines two connected modes:
1. Reliable Connected(RC)
2. Unreliable Connected(UC)
The two modes differ mainly, as is evident from the nomenclature,
in providing reliability of data delivery across the connection.
This document applies equally to both the connected modes - IPoIB
over these two modes is referred to as IPoIB-CM (connected mode)
in this document. IPoIB over reliable connected mode is referred
to as IPoIB-RC whereas IPoIB over unreliable connected mode is
referred to as IPoIB-UC where applicable. For clarity IPoIB over
the unreliable datagram mode, as described in [IPoIB_ENCAP] and
[IPoIB_MCAST], is referred to as IPoIB-UD.
The connected modes offer link MTUs of up to 2^31 bytes in length.
Thus the use of connected modes can offer significant benefits by
supporting reasonably large MTUs. The datagram modes of IBA are
limited to 4096 bytes. Reliability is also enhanced by the
underlying feature of 'automatic path migration' supported by the
connected modes is utilised [IB_ARCH].
This document presents a method of address resolution and
transmission of IP packets over connected modes of IBA.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
in this document are to be interpreted as described in RFC 2119.
2.0 IPoIB-connected mode
The connected modes of IBA define a non-broadcast, multiple access
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network - the connected modes of IBA do not support multicasting
though every node can communicate with every other node if
desired.
This implies that intrinsically one cannot rely on native
broadcast or multicast to send out the address resolution query.
But an ARP server is not an efficient solution. Fortunately in the
case of IPoIB-CM there is a way out as explained below.
2.1 Outline of Address Resolution
IBA requires that all Host Channel Adapters(HCAs) support the
reliable and unreliable connected modes[IB_ARCH]. It is optional
for Target Channel Adapters (TCAs) to support the connected modes.
At the same time IBA requires all HCAs and TCAs to support
unreliable datagram mode. The unreliable datagram mode does
support multicasting. IPoIB over unreliable datagram(IPoIB-UD) as
presented in [IPoIB_MCAST]/[IPoIB_ENCAP] requires the IB subnet to
support IB level multicast.
Therefore it is possible to use a multicast query over IB-UD
for IPoIB-CM address resolution.
[IPoIB_ENCAP] proposes that the address resolution query is
multicast over an IB multicast address that is joined by every
member of the IPoIB subnet. This IB multicast address is referred
to as the 'broadcast-GID' [IPoIB_ENCAP]. This document extends the
requirement of joining the 'broadcast-GID' to IPoIB-CM too by
associating an unreliable datagram queue-pair with every IPoIB-CM
interface.
A broadcast-GID is formed with the knowledge of the scope bits, IP
version, the partition key(P_Key) associated with the subnet. Thus
these three parameters must be known to the node before an IPoIB
interface can be brought up. The exact format and rules to setup
the broadcast-GID are defined in [IPoIB_MCAST].
2.2 Outline of Connection setup
Address resolution is but the first step. Once the link address of
the remote node is known an IB connection must be setup between the
nodes before any IP communication may occur.
To make a connection, the sender must know the service-ID to use
in the request to make a connection [IB_ARCH]. It must also supply
the queue pair to the remote node. The peer replies with its queue
pair. Note that each IB connection is peer to peer and uses one
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connected mode QP at each end.
Though the address resolution occurs at an individual IP address
level the connection between the nodes is at the IB layer.
Therefore every individual address resolution does not imply a new
connection between the peers.
3.0 Address Resolution
Every IPoIB-CM node MUST join the broadcast-GID associated with the
subnet [IPoIB_MCAST]. This join is over an UD QP. The address
resolution query is always sent out on the broadcast-GID.
An IPoIB-CM implementation MAY use the same unreliable
datagram(UD) queue pair(QP) as used by the IPoIB-UD implementation
if the latter mode is supported in the same partition and scope.
Therefore the address resolution query is sent to the
broadcast-GID on the associated UD QP. A unicast
reply is received on the UD QP associated with IPoIB-CM.
Note:
The IPoIB-CM link need not be the same as the link defined by
IPoIB-UD. In other words the broadcast-GID used for an
IPoIB-CM is independent of other broadcast-GIDs supported over
the same IB subnet. It MAY be the same but is not required to
be the same.
IPoIB encapsulation [IPoIB_ENCAP] describes the link-layer address
as follows:
<1 octet reserved>:QP: GID
This document extends the link-layer address as follows:
<flags>:QP:GID
Flags:
This is a single octet field. If bit 0 is set then it
implies that in the sender's view,the subnet is built over
IB's 'reliable connected' i.e. RC mode. If bit 1 is set
then it implies that the subnet is built over IB's
'unreliable connected' i.e. UC mode. All other bits in the
octet are reserved and MUST be set to 0.
Both the RC and UC flags MUST not be set at the same time.
They are mutually exclusive.
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The format of the flags is:
+--+--+--+--+--+--+--+--+
|RC|UC| 0| 0| 0| 0| 0| 0|
+--+--+--+--+--+--+--+--+
Note:
The above implies that a given IP subnet can only be
supported on one InfiniBand mode. If the link layer
includes no flags then it is part of an IPoIB-UD
subnet, if the link layer includes the RC flag then
it is part of an IPoIB-RC subnet, if the link layer
includes the UC flag then it is part of an IPoIB-UC
subnet.
QPN:
The queue-pair number(QPN) on which the unicast address
resolution reply will be received. This allows the
IPoIB-UD address resolution code and method can be used
for IPoIB-CM address resolution.
The QPN also serves another purpose. It is used to form
the Service-ID that is used to setup the IB connection.
On receiving the multicast/broadcast address resolution request
the receiver replies with its own link-address, including the
associated UD QPN and the appropriate flag. If the flags do not
match then there is a misconfiguration since the underlying IB
modes do not match. In such a case a suitable error indication
SHOULD be provided to the administrator.
The receiver's reply is unicast back to the sender after the
receiver has, as in the case of IPoIB over unreliable
datagram(IPoIB_UD), resolved the GID to the LID and determined
other required parameters[IPoIB_ENCAP].
Once the address resolution is completed the underlying IB
connection can be setup.
4.0 IB Connection Setup
The IB reliable/unreliable mode connection may be setup by any of
the peers though it is more likely that the one that initiated the
address resolution phase, probably as a result of the need to send
IP data, will initiate the connection setup. IBA allows
passive-active and active-active connection setup.
To setup a connection IB Management Datagrams (MADs) are directed
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to the peer's communication manager(CM). The connection request
always contains a Service-ID for the peer to associate the request
with the appropriate entity. If the request is accepted the peer
returns the relevant connected mode QPN in the response MAD. This
content of the CM connection messages and the IB connection setup
is described in[IB_ARCH].
The CM messages include, among other parameters, the Service-ID,
Local QPN, and the payload size to use over the connection.
Note: The IB connection is setup using the Service-ID as defined
above. The node MUST keep a record of IB connections it is
participating in. The node SHOULD NOT attempt another
connection to the remote peer using the same Service-ID as
used for an existing IB connection.
4.1 Service-ID
The InfiniBand specification defines a block of service IDs for
IETF use. The InfiniBand specification has left the definition and
management of this block to the IETF[IB_ARCH]. The 64-bit block
is:
+--------+--------+--------+--------+--------+--------+--------+--------+
|00000001|<-------------------IETF use--------------------------------->|
+--------+--------+--------+--------+--------+--------+--------+--------+
The Service-IDs used by IPoIB will be in the format:
+--------+--------+--------+--------+--------+--------+--------+--------+
|00000001| Type |Reserved| QPN | Reserved |
+--------+--------+--------+--------+--------+--------+--------+--------+
The Reserved fields MUST be transmitted as zeroes. They are
ignored on reception.
The QPN MUST be the value exchanged during address
resolution.
The Type MUST be set to 0.
Note:
The service-ID formed using the UD QPN used for address
resolution MUST be supported by the associated interface.
4.2 MTU
The IB connection setup might be used for both IPv4 and IPv6 or it
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could be used for only one of them while a different connection is
used for the other. The link MTU MUST be able to support the
minimum MTU required by the protocols.
Every connection setup message includes a 'private data'
field[IB_ARCH]. The private data field MUST carry the following
information:
0 15
+----------------+
| Desired MTU |
+----------------+
| Minimum MTU |
+----------------+
The connection setup message (CM REQ) MUST insert the requested
MTU in the 'Desired MTU' field and the minimum acceptable MTU in
the 'Minimum MTU' field. If it is not acceptable to the peer then
it MUST indicate the preferred value in the 'desired MTU' when
rejecting (CM REJ) the request. If the 'desired MTU' is lower than
the minimum MTU that can be supported, the connection MUST be
rejected (CM REJ message) with the minimum acceptable MTU set in
both the desired and minimum MTU fields.
5.0 IP encapsulation
The IP encapsulation will be done as defined in the IPoIB
encapsulation standard[IPoIB_ENCAP].
IP multicast cannot be done over the IPoIB-CM modes. Multicast
traffic MUST be transmitted over the UD QP associated with the
IPoIB-CM interface.
6.0 Security Considerations
A node may be returned a false set of flags by an impostor. This
may cause unnecessary attempts and some delay/disruption in IPoIB
communication. The same is the case if wrong/spurious QPN
values are provided during address resolution broadcast/multicast.
The same precautions MUST be taken as described in the 'security
considerations' section of [IPoIB_MCAST] and [IPoIB_ENCAP] .
7.0 References
[IB_ARCH] InfiniBand Architecture Specification, version 1.1
www.infinibandta.org
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[IPoIB_ARCH] draft-ietf-ipoib-architecture-02.txt, V. Kashyap
[IPoIB_ENCAP] draft-ietf-ipoib-ip-over-infiniband-04.txt,
V. Kashyap, H.K. Jerry Chu
[IPoIB_MCAST] draft-ietf-ipoib-link-multicast-04.txt,
H.K. Jerry Chu, V. Kashyap
7.0 Author's Address
Vivek Kashyap
15450, SW Koll Parkway
Beaverton, OR 97006
Phone: +1 503 578 3422
Email: vivk@us.ibm.com
Full Copyright Statement
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