INTERNET-DRAFT Donald Eastlake
Intended status: Proposed Standard Weiguo Hao
Lili Wang
Yizhou Li
Shunwan Zhuang
Huawei
Expires: March 17, 2019 September 18, 2018
Centralized EVPN DF Election
draft-hao-bess-evpn-centralized-df-02.txt
Abstract
This document proposes a centralized DF Designated Forwarder election
mechanism to be used between an SDN (Software Defined Network)
controller and each PE (Provider Edge) device in an EVPN network.
Such a mechanism overcomes the issues of current standalone DF
election defined in RFC 7432. A new BGP capability and an additional
DF Election Result Route Type are specified to support this
centralized DF mechanism.
Status of this Memo
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D. Eastlake, et al [Page 1]
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Table of Contents
1. Introduction............................................3
2. Conventions used in this document.......................4
3. Solution Overview.......................................5
3.1 Centralized DF Election Capability.....................5
4. DF Election Result Route Type...........................7
4.1 DF Election Result Route Encoding......................7
4.2 Centralized DF Election procedures.....................9
5. Security Considerations................................10
6. IANA Considerations....................................11
Normative References......................................12
Informative References....................................12
Acknowledgments...........................................13
Authors' Addresses........................................13
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1. Introduction
[RFC7432] defines the Designated Forwarder (DF) election mechanism in
EVPN networks to appoint one PE as DF from a candidate list of PEs
and VLANs (or VLAN bundles) connecting to a multi-homed CE device or
access network. The DF PE is responsible for sending broadcast,
multicast and unknown unicast traffic (BUM) to the multi-homed CE
device or network and non-DF PEs must drop such traffic. This DF
based mechanism is used to prevent duplicated packet injection into
the multi-homed access network via multiple PEs.
In [RFC7432] the DF is selected according to the VLAN modulus
"service-carving" algorithm in order to perform load balancing for
multi-destination traffic destined to a given segment]. The algorithm
can ensure each participating PE independently and unambiguously
determines which one of the participating PEs is the DF; however, use
of this algorithm has some drawbacks as follows [EVPN-HRW-DF].
1. Uneven load balancing in some VLAN configuration cases when the
Ethernet tags have a non-uniform distribution, for instance when
the Ethernet tags are all even or all odd.
2. Unnecessary service disruption when PEs join or leave a redundancy
group. In Figure 1 below, say v1, v2 and v3 are VLANs configured
on ES2 with associated Ethernet tags of value 3, 4 and 5
respectively. So PE1, PE2 and PE3 are also the DFs for v1, v2 and
v3 respectively. Now when PE3 goes down, PE2 will become the DF
for v1 and v3 while PE1 will become the DF for v2, needless churn
of v1 and v2 occurs, and it will cause unnecessary service
disruption in v1 and v2.
3. Lack of user control over DF election. In some cases, the user may
want to flexibly control the load balancing based on VLAN number,
bandwidth consumption, and other factors. The user should be
allowed to use some specific DF re-election algorithm to avoid
service disruption. The user also should be allowed to specify
revertive and non-revertive mode for on-demand DF switchover in
order to carry out some maintenance tasks.
This document specifies a centralized DF election method to overcome
the issues aforementioned. A physically distributed but logically
centralized controller is deployed to perform the DF election
calculation for all multi-homed PEs. Each individual multi-homed PE
should disable its own DF election process and listen to the DF
election result from the SDN controller. [RFC7432] DF election
procedures are extended for the interaction between the SDN
Controller and each PE.
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2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The following terms and acronyms are used:
CE: Customer Edge device, e.g., a host, router, or switch.
DF: Designated Forwarder.
Ethernet Segment (ES): When a customer site (device or network) is
connected to one or more PEs via a set of Ethernet links,
then that set of links is referred to as an "Ethernet
segment".
ESI: Ethernet Segment Identifier: A unique non-zero identifier
that identifies an Ethernet segment.
EVI: An EVPN instance spanning the Provider Edge (PE) devices
participating in that EVPN.
EVPN: Ethernet Virtual Private Network.
PE: Provider Edge device.
NLRI: Network Layer Reachability Information.
SDN: Software Defined Networking.
VLAN: Virtual Local Area Network.
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3. Solution Overview
------------------
| SDN Controller |
------------------
|
-------------------------------------------
/ \
| MPLS EVPN Network |
\ /
-------------------------------------------
| | | | |
------- ------- ------- ------- -------
| PE1 | | PE2 | | PE3 | | PE4 | | PE5 |
------- ------- ------- ------- -------
\ | / \ /
\ | / \ /
\ | / \ /
------- -------
| CE1 | | CE2 |
------- -------
Figure 1. Centralized DF Election Scenario
In Figure 1, CE1 is multi-homed to PE1, PE2 and PE3, the ESI is 1.
CE2 is multi-homed to PE4 and PE5, the ESI is 2. The SDN controller
will be pre-provisioned with the entire network's ESI related
configuration. This includes EVI, the Ethernet Tags on each ESI,
redundancy mode of active-active or active-standby for each ESI,
<ESI, Ethernet Tag> and EVI correspondence.
Before each PE and the SDN controller exchange BGP route information
for DF election, the SDN controller and each PE MUST negotiate a new
BGP centralized DF election capability and role when OPEN messages
are first exchanged; each PE participating in multi-homing is the
client for the DF election information while the SDN controller is
the server. For these PEs the regular DF election process as per
[RFC7432] will be disabled and each PE listens to the DF/Non-DF
result from the SDN controller at the granularity of <ES,VLAN> or
<ES, VLAN bundle>. For the DF election server, after it receives
Ethernet Segment route from each PE, it will perform DF election
calculation based on a local algorithm and will notify each EVPN PE
of the election result through a new EVPN route type.
3.1 Centralized DF Election Capability
The centralized DF election capability is a new BGP capability
[RFC5492] that can be used by a BGP speaker to indicate its ability
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to support for the new DF election process.
This capability is defined as follows:
Capability code: TBD1
Capability length: 2 octets
Capability value: Consists of the "Election Flags" field and
"Holding Time" field as follows:
| 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| Election | Holding Time in seconds |
| Flags | |
| (4 bits) | (12 bits) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The use and meaning of these fields are as follows:
Election Flags: This field contains bit flags related to
restart as follows:
| 0 1 2 3|
+---+---+---+---+
| C | S | Resv |
+---+---+---+---+
C: The most significant bit is the election Client bit. When
set to 1 it indicates the BGP speaker is a Client which
will await the DF election result from the Controller
(Server).
S: When set to 1, this bit indicates that the BGP speaker is
the Server (Controller) that has the DF election
calculation capability for all multi-homed PEs in the
entire EVPN network.
Resv: Reserved bits that MUST be sent as zero and ignored on
receipt.
Holding Time: This is the estimated maximum time in seconds it
will take for the client to get DF election result from the
controller after the BGP session is established. When no
result for the DF election is received after the holding
time, PEs will revert to the traditional EVPN DF election
process as per [RFC7432].
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4. DF Election Result Route Type
The current BGP EVPN NLRI as defined in [RFC7432] is shown below:
+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
This document defines an additional Route Type used for the server
(SDN Controller) to send DF election results to each client (PE).
The Route Type is "DF Election Result Route Type".
The detailed encoding of this route and associated procedures are
described in the following sections.
4.1 DF Election Result Route Encoding
The route type specific information for a DF Election Result Route
NLRI consists of the following fields:
Route Type specific information:
+--------------------------------------+
| RD (8 octets) |
+--------------------------------------+-------+
| Ethernet Segment Identifier (10 octets) |
+----------------------------------------------+
| TLVs ...
+-------------------------------------
Figure 2: DF Election Result Router Type specific information
RD: The Route Distinguisher (RD) MUST be a Type 1 RD [RFC4364].
The value field comprises an IP address of the Controller
(typically, the loopback address) followed by a number unique
to the Controller.
ESI: Ethernet Segment Identifier: Is a non-zero 10-octet
identifier for an Ethernet Segment.
TLVs: Information in the TLVs field is encoded in
Type/Length/Value triplets. Multiple TLVs can be included. This
document specifies type 1, the VLAN Bitmap type, whose
structure is as follows:
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+-----------------------------------------+
| DF Election Result Type = 1 | (2 octets)
+-----------------------------------------+
| Length | (2 octets)
+------------------------+----------------+
|IP Address Prefix Length| (1 octet)
+------------------------...----------------------+
| Client PE IP Address (4 or 16 octets) |
+------------------------...----------------------+
| RESV | Start VLAN ID | (2 octets)
+-----------------------------------------+
| VLAN bit-map.... ...
+------------------------------
Figure 3. DF Election Result TLV Format
o DF Election Result Type (2 octets): Identifies the type
of DF Election result. This document defines type 1 as
the "VLAN Bitmap" Type. TLVs withe unknown types are
ignored and skipped upon receipt.
o Length (2 octets): The total number of octets of the
value part of the TLV.
The type and length are followed by the variable length value.
This value, for the VLAN Bitmap type, consists of the following
fields:
o The IP Prefix Length can be set to a value between 0 and
32 (bits) for ipv4 and between 0 and 128 for ipv6.
o The Client PE IP Address will be a 32 or 128-bit field
(ipv4 or ipv6) as PE's identification.
o RESV is a 4-bit reserved field that MUST be sent as zero
and ignored on receipt.
o Start VLAN ID: The 12-bit VLAN ID that is represented by
the high order bit of the first byte of the VLAN bit-map.
o VLAN bit-map: The highest order bit indicates the VLAN
equal to the start VLAN ID, the next highest bit
indicates the VLAN equal to start VLAN ID + 1, continuing
to the end of the VLAN bit-map field. A bit value of 1
indicates DF and a bit value of 0 indicates non-DF.
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4.2 Centralized DF Election procedures
The controller has all ES related configuration information for the
entire EVPN network. After the controller boots up, it can start a
boot-timer to allow the establishment of BGP EVPN sessions with all
multi-homed EVPN PEs. The controller also needs to receive all ES
routes from those PEs before the boot-timer timeout. The controller
will preserve all EVPN PE's ES routes.
Based on a local algorithm for each ES, it can start to perform the
DF election calculation. The default algorithm is the VLAN modulus
method defined in section 8.5 [RFC7432] relying on local VLAN
configuration on each ES. A user defined algorithm should be allowed.
After the DF election calculation is finished on the controller, it
will notify each multi-homed PE using the newly defined DF Election
Result Route. The DF Election Result Route is per ES, i.e., the DF
election results for all PEs connecting to the same ES are carried in
one route. The controller that advertises the Ethernet Segment route
must carry an ES-Import Route Target. The DF Election Result
filtering procedure is the same as the Ethernet Segment route
filtering defined in [RFC7432], i.e., the DF Election Result Route
filtering MUST be imported only by the PEs that are Multi-homed to
the same Ethernet segment. Each Multi-homed PE compares the Client PE
IP Address with its local IP Address, if the two IP addresses are
same, then it gets the corresponding start VLAN and VLAN Bitmap as
the DF election results.
When the failure of a multi-homed PE is detected by the controller,
the controller will initiate the DF re-election process. Because
it's the controller making decisions as to which PE is DF or non-DF,
the controller should ensure that the DF re-election won't cause
unnecessary service disruption. In the example above, the controller
should only redistribute the DF VLAN on PE3 to PE1 and PE2, the
existing DF VLAN on PE1 and PE2 should remain unchanged to avoid
service disruption.
When the access link fails on one multi-homed PE, the PE will
advertise an Ethernet Segment Withdraw message to the controller,
which will trigger the DF re-election on the controller, the re-
election principle is same as in the node failure case to minimize
service disruption.
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5. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the BGP security model. The communications between the SDN
Controller and EVPN PEs should be protected to ensure security. BGP
peerings are not automatic and require configuration, thus it is the
responsibility of the network operator to ensure that they are
trusted entities.
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6. IANA Considerations
Three IANA actions are requested as below.
IANA is requested to assign a new BGP Capability Code in the
Capability Code registry as follows:
Value Description Reference
------ ----------------------- ---------------
TBD1 Centralized DF Election [this document]
This document requested the assignment of value TBD2 in the "EVPN
Route Types" registry created by [RFC7432] and modification of the
registry to add the following:
Value Description Reference
------ ------------------ ---------------
TBD2 DF Election Result [this document]
IANA is requested to create a registry for "DF Election Result Types"
as follows:
Name: DF Election Result Types
Registration Procedure: First Come First Served
Reference: [this document]
Type Description Reference
-------- ------------- ---------
0 (Reserved)
1 VLAN Bitmap [this document]
2-65534 unassigned
65535 (reserved)
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Normative References
[RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119,
March 1997, <http://www.rfc-editor.org/info/rfc2119>.
[RFC4364] - Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC5492] - Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 2009,
<https://www.rfc-editor.org/info/rfc5492>.
[RFC7432] - Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015,
<http://www.rfc-editor.org/info/rfc7432>.
[RFC8174] - Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May
2017, <https://www.rfc-editor.org/info/rfc8174>.
Informative References
[EVPN-HRW-DF] - Mohanty S. et al. "A new Designated Forwarder
Election for the EVPN", draft-mohanty-bess-evpn-df-election-02,
work-in-progress, October 19, 2015.
D. Eastlake, et al [Page 12]
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Acknowledgments
The authors wish to acknowledge the important contributions of
Qiandeng Liang.
Authors' Addresses
Donald Eastlake, 3rd
Huawei Technologies
1424 Pro Shop Court
Davenport, FL 33896 USA
Email: d3e3e3@gmail.com
Weiguo Hao
Huawei Technologies
101 Software Avenue,
Nanjing 210012, China
Email: haoweiguo@huawei.com
Lili Wang
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095, China
Email: lily.wong@huawei.com
Yizhou Li
Huawei Technologies
101 Software Avenue,
Nanjing 210012, China
Email: liyizhou@huawei.com
Shunwan Zhuang
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing, 100095 China
Email: zhuangshunwan@huawei.com
D. Eastlake, et al [Page 13]
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D. Eastlake, et al [Page 14]