IDR Working Group W. Wang
Internet-Draft A. Wang
Intended status: Standards Track China Telecom
Expires: February 25, 2021 H. Wang
Huawei Technologies
G. Mishra
Verizon Inc.
S. Zhuang
J. Dong
Huawei Technologies
August 24, 2020
Route Distinguisher Outbound Route Filter (RD-ORF) for BGP-4
draft-wang-idr-rd-orf-03
Abstract
This draft defines a new Outbound Route Filter (ORF) type, called the
Route Distinguisher ORF (RD-ORF). RD-ORF is applicable when the
routers do not exchange VPN routing information directly (e.g.
routers in single-domain connect via Route Reflector, or routers in
Option B/Option AB/Option C cross-domain scenario).
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on February 25, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. RD-ORF Encoding . . . . . . . . . . . . . . . . . . . . . . . 5
5. Application in single-domain scenario . . . . . . . . . . . . 7
5.1. Addition of RD-ORF entries . . . . . . . . . . . . . . . 7
5.1.1. Operation process of RD-ORF mechanism on source PE . 7
5.1.2. Operation process of RD-ORF mechanism on RR . . . . . 8
5.1.3. Operation process of RD-ORF mechanism on target PE . 8
5.2. Withdraw of RD-ORF entries . . . . . . . . . . . . . . . 9
6. Applications in cross-domain scenarios . . . . . . . . . . . 9
6.1. Application in Option B/Option AB cross-domain scenario . 9
6.2. Application in Option C cross-domain scenario . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 12
10. Normative References . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
With the rapid growth of network scale, Route Reflector is introduced
in order to reduce the network complexity. Routers in the same
Autonomous System only need to establish iBGP session with RR to
transmit routes.
In VPN scenario shown in Figure 1, PE1 - PE4 establish IBGP sessions
with RR to ensure the routes can be transmitted within AS100, where
PE1 and PE3 maintain VRFs of VPN1 and VPN2, PE2 maintains VPN1's VRF
and PE4 maintains VPN2's VRF. RR don not maintain any VRFs.
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+----------------------------------------------+
| |
| |
| +---------+ +---------+ |
| | PE1 | | PE4 | |
| +---------+ +---------+ |
| VPN1 \ / VPN2 |
| VPN2 \+---------+ / |
| | | |
| | RR | |
| | | |
| +---------+ \ |
| / \ |
| +---------+/ +---------+ |
| | PE2 | | PE3 | |
| +---------+ +---------+ |
| VPN1 VPN1 |
| AS 100 VPN2 |
+----------------------------------------------+
Figure 1: Single-domain scenario
When the VRF of VPN1 in PE1 overflows, due to PE1 and other PEs are
not iBGP neighbors, BGP Maximum Prefix Features cannot work, so the
problem on PE2 cannot be known.
Now, there are several solutions can be used to alleviate this
problem:
o Route Target Constraint (RTC) as defined in [RFC4684]
o Address Prefix ORF as defined in [RFC5292]
o PE-CE edge peer Maximum Prefix
o Configure the Maximum Prefix for each VRF on edge nodes
However, there are limitations to existing solutions:
1) Route Target Constraint
RTC can only filter the VPN routes from the uninterested VRFs, if the
"trashing routes" come from the interested VRF, filter on RTs will
erase all prefixes from this VRF.
2) Address Prefix ORF
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Using Address Prefix ORF to filter VPN routes need to pre-
configuration, but it is impossible to know which prefix may cause
overflow in advance.
3) PE-CE edge peer Maximum Prefix
This mechanism can only protect the edge between PE-CE, it can't be
deployed within PE that peered via RR. Depending solely on the edge
protection is dangerous, because if only one of the edge points being
comprised/error-configured/attacked, then all of PEs within domain
are under risk.
4) Configure the Maximum Prefix for each VRF on edge nodes
When a VRF overflows, PE will break down the BGP session with RR
according to the Maximum Prefix mechanism. However, there may have
several VRFs on PE rely on the PE-RR session, this mechanism will
influence other VRFs.
This draft defines a new ORF-type, called the Route Distinguisher ORF
(RD-ORF). Using RD-ORF mechanism, VPN routes of a VPN can be
controlled based on source RD and originator. This mechanism is
event-driven and does not need to be pre-configured. When a VRF of a
router overflows, the router will find out the main source address
and RD of VPN routes in this VRF, and send a RD-ORF to its BGP peer
that carrys the RD and the source address. If a BGP speaker receives
a RD-ORF from its BGP peer, it will filter the VPN routes it tends to
send according to the RD-ORF entry.
RD-ORF is applicable when the routers do not exchange VPN routing
information directly (e.g. routers in single-domain connect via Route
Reflector, or routers in Option B/Option AB/Option C cross-domain
scenario).
2. Conventions used in this document
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 [RFC2119] .
3. Terminology
The following terms are defined in this draft:
o RD: Route Distinguisher, defined in [RFC4364]
o ORF: Outbound Route Filter, defined in [RFC5291]
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o AFI: Address Family Identifier, defined in [RFC4760]
o SAFI: Subsequent Address Family Identifier, defined in [RFC4760]
o EVPN: BGP/MPLS Ethernet VPN, defined in [RFC7432]
o RR: Router Reflector, provides a simple solution to the problem of
IBGP full mesh connection in large-scale IBGP implementation.
o VRF: Virtual Routing Forwarding, a virtual routing table based on
VPN instance.
4. RD-ORF Encoding
In this draft, we defined a new ORF type called Route Distinguisher
Outbound Route Filter (RD-ORF). The ORF entries are carried in the
BGP ROUTE-REFRESH message as defined in [RFC5291]. A BGP ROUTE-
REFRESH message can carry one or more ORF entries, and MUST be
regenerated when it is tended to be sent to other BGP peers. The
ROUTE-REFRESH message which carries ORF entries contains the
following fields:
o AFI (2 octets)
o SAFI (1 octet)
o When-to-refresh (1 octet): the value is IMMEDIATE or DEFER
o ORF Type (1 octet)
o Length of ORF entries (2 octets)
A RD-ORF entry contains a common part and type-specific part. The
common part is encoded as follows:
o Action (2 bits): the value is ADD, REMOVE or REMOVE-ALL
o Match (1 bit): the value is PERMIT or DENY
o Reserved (5 bits)
RD-ORF also contains type-specific part. The encoding of the type-
specific part is shown in Figure 2.
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+-----------------------------------------+
| |
| Sequence (4 octets) |
| |
+-----------------------------------------+
| |
| Route Distinguisher (8 octets) |
| |
+-----------------------------------------+
| |
|Source Address sub-TLV (4,6 or 16 octets)|
| |
+-----------------------------------------+
Figure 2: RD-ORF type-specific encoding
o Sequence: identifying the order in which RD-ORF is generated
o Route Distinguisher: distinguish the different user routes. The
RD-ORF filters the VPN routes it tends to send based on Route
Distinguisher.
o Source Address sub-TLV: the source address is TLV format, which
contains the following sub-TLVs:
* In single-domain or Option C cross-domain scenario, NEXT_HOP
attribute is fixed during routing transmission, so it can be
used as source address.
Type = 1, Length = 4 or 16 octets, value = NEXT_HOP.
* In Option B or Option AB cross-domain scenario, NEXT_HOP
attribute may be changed by ASBRs and cannot be used as the
source address. The originator can be traced by the Route
Origin Community in BGP (as defined in Section 5 of [RFC4360]).
Type = 2, Length = 6 octets, value = the value field of
Route Origin Community.
Note that if the Action component of an ORF entry specifies REMOVE-
ALL, the ORF entry does not include the type-specific part.
When the BGP ROUTE-REFRESH message carries RD-ORF entries, it must be
set as follows:
o The ORF-Type MUST be set to RD-ORF.
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o The AFI MUST be set to IPv4, IPv6, or Layer 2 VPN (L2VPN).
o If the AFI is set to IPv4 or IPv6, the SAFI MUST be set to MPLS-
labeled VPN address.
o If the AFI is set to L2VPN, the SAFI MUST be set to BGP EVPN.
o The Match field MUST be equal to DENY.
5. Application in single-domain scenario
5.1. Addition of RD-ORF entries
The operation of RD-ORF mechanism on each device is independent, each
of them makes a local judgement to determine whether it needs to send
RD-ORF to its peers.
In general, every VRF on PE is configured a Maximum Prefix, the
trigger of RD-ORF mechanism can be set as the number of VPN routes in
VRF reach 80% of the Maximum Prefix. For RR, it doesn't have VRF and
the machanism can be triggered by other conditions, such as the RR's
memory/CPU utilization reaches 80%.
When the RD-ORF mechanism is triggered, the device must send an alarm
information to network operators.
5.1.1. Operation process of RD-ORF mechanism on source PE
In scenario shown in Figure 1, when the VRF of VPN1 in PE1 overflows,
PE1 will do analysis and calculation locally to find out the main
source of VPN routes in this VRF, assuming it is PE3. Then, PE1 will
resolve the host address and corresponding RD of VPN routes from BGP
UPDATE message, and generate a BGP ROUTE-REFRESH message contains a
RD-ORF entry, and send it to RR. The message contains the following
fields:
o AFI is set to IPv4 , IPv6 or L2 VPN
o SAFI is set to "MPLS-labeled VPN address" or "BGP EVPN"
o When-to-refresh is set to IMMEDIATE
o ORF Type is set to RD-ORF
o Length of ORF entries depends on the type of Source Address sub-
TLV (21, 23 or 33 octets)
o Action is set to ADD
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o Match is set to DENY
o Sequence is set to 1
o Route Distinguisher is set to RD1
o Source Address sub-TLV is set to PE3's host address
It noted that the Sequence can uniquely identifies an RD-ORF entry.
All VRFs share the sequence field, and the corresponding sequence of
RD-ORF sent by each VRF will be recorded on the device.
5.1.2. Operation process of RD-ORF mechanism on RR
When RR receives the ROUTE-REFRESH message, it checks <AFI/SAFI, ORF-
Type, Sequence, Route Distinguisher, Source Address sub-TLV> to find
whether it received the latest entry or not. If not, RR will discard
the entry; otherwise, RR will add the RD-ORF entry into its Adj-RIB-
out.
Before sending a VPN route toward PE1, RR will check its Adj-RIB-out
and find there is a filter associated with <RD1, PE3's host address>.
Then, RR will stop sending that VPN route to PE1.
If the processing capacity of RR reaches the limit (e.g. RR's
memory/CPU utilization reaches 80%), RR will find out the peer that
sends the most routing entries to it, assuming it is PE3. Then, RR
will generate a BGP ROUTE-REFRESH message contains a RD-ORF entry
based on the result of calculation, and send it to PE3.
5.1.3. Operation process of RD-ORF mechanism on target PE
After receiving the ROUTE-REFRESH message that carries a RD-ORF
entry, PE3 will check if it receives the latest entry. If not, PE3
will discard it; otherwise, PE3 will add the RD-ORF entry into its
Adj-RIB-out.
Before sending a VPN route toward RR, PE3 will check its Adj-RIB-out
and find the RD-ORF entry prevent it from sending VPN route which
carries RD1 to RR. Then, PE3 will stop sending that VPN route.
The BGP Maximum Prefix Features can be configured to protect PE-CE
peering at the edge. Therefore, in general, CEs will not cause the
overflow of PEs. If the boundary protection measures fail and cause
the overflow, the PE can calculate and find the CEs in corresponding
VRF, and break down the associated BGP sessions.
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5.2. Withdraw of RD-ORF entries
When the RD-ORF mechanism is triggered, the alarm information will be
generated and sent to the network operators. Operators should
manually configure the network to resume normal operation. Due to
devices can record the RD-ORF entries sent by each VRF, operators can
find the entries needs to be withdrawn, and trigger the withdraw
process as described in [RFC5291] manually to delete them on RR/ASBR/
target PE after network recovery.
6. Applications in cross-domain scenarios
6.1. Application in Option B/Option AB cross-domain scenario
The Option B/Option AB cross-domain scenario is shown in Figure 3:
+--------------------------+ +--------------------------+
| | | |
| | | |
| +---------+ | | +---------+ |
| | PE1 | | | | PE3 | |
| +---------+ | | +---------+ |
| VPN1 \ | | / VPN1 |
| VPN2 \+---------+ EBGP +---------+/ VPN2 |
| | | | | |
| | ASBR1 |-----------| ASBR2 | |
| | | | | |
| +---------+ +---------+ |
| / | | \ |
| +---------+/ | | \+---------+ |
| | PE2 | | | | PE4 | |
| +---------+ | | +---------+ |
| VPN1 | | VPN2 |
| AS1 | | AS2 |
+--------------------------+ +--------------------------+
Figure 3: The Option B/Option AB cross-domain scenario
In Option B cross-domain scenario, PE1 - PE4 are responsible for
maintaining VPN routing information in AS1 and AS2. There is a
direct link between ASBR1 and ASBR2 via EBGP. In AS1, PE1 and PE2
establish IBGP sessions with ASBR1 to ensure the routes can be
transmitted in AS1. In AS2, PE3 and PE4 establish IBGP session with
ASBR2.
Due to the maintenance of VPN routes is only done by PEs. ASBRs
cannot know whether the PEs' ability to handle VPN routes has reached
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the upper limit or not, so it needs the RD-ORF to control the number
of routes.
Assume that PE1 - PE4 can transmit VPN routes through the network
architecture shown in Figure 3. When the VRF of VPN1 in PE1
overflows, the RD-ORF mechanism will be implemented as follows:
1) PE1 will check and find out the main source of VPN routes in this
VRF is PE3. Then, PE1 will resolve the host address and
corresponding RD from BGP UPDATE message, and generate a BGP ROUTE-
REFRESH message contains an RD-ORF entry, and send it to ASBR1.
2) When ASBR1 receives the ROUTE-REFRESH message, it checks whether
it receives the latest RD-ORF entry. If not, ASBR1 will discard the
entry; Otherwise, ASBR1 will add the RD-ORF entry into its Adj-RIB-
out.
Before sending a VPN route toward PE1, RR will check its Adj-RIB-out
and find there is a filter associated with <RD1, PE3's host address>.
Then, ASBR1 will stop sending that VPN route.
Besides, ASBR1 will locally determine if it needs to send an RD-ORF
entry to ASBR2. The judgment criteria refers to Section 5.1.2.
3) If ASBR2/PE3 receives the RD-ORF entry, it will repeat the above
process.
When the RD-ORF mechanism is triggered, network operators need to
manually configure the network to return to resume normal operation.
The withdraw of RD-ORF entries refers to Section 5.2.
In Option AB cross-domain scenario, ASBRs maintain VRFs. However,
due to VPN routes in all VRFs use the same BGP session, ASBRs cannot
prevent the overflow of a certain VRF by breaking down a BGP session.
The operation process of RD-ORF is similar to that in Option B
scenario.
6.2. Application in Option C cross-domain scenario
The Option C cross-domain scenario is shown in Figure 4:
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MP-EBGP
+----------------------------------------+
| |
+------------+------------+ +------------+------------+
| +----+----+ | | +----+----+ |
| | | | | | | |
| +----+ RR1 +----+ | | +----+ RR2 +----+ |
| | | | | | | | | | | |
| | +---------+ | | | | +---------+ | |
| | | | | | | |
| |IBGP IBGP| | | |IBGP IBGP| |
| | | | | | | |
+-+--+----+ +----+--+-+ +-+--+----+ +----+--+-+
| | | | | | | |
| PE1 | | ASBR1 |----------| ASBR2 | | PE2 |
| | | | | | | |
+-+-------+ AS1 +-------+-+ +-+-------+ AS2 +-------+-+
+-------------------------+ +-------------------------+
Figure 4: The Option C cross-domain scenario
In this scenario, PE1 and PE2 are responsible for maintaining VPN
routing information in AS1 and AS2. In order to reduce the
complexity that full-mesh brings to the network, RR1 and RR2
establish MP-EBGP session to transmit labeled routes. In AS1, PE1
and ASBR1 establish IBGP session with RR1 to ensure the routes can be
transmitted in AS1. In AS2, PE2 and ASBR2 establish IBGP session
with RR2.
Due to the maintenance of VPN routes is only done by PEs. RRs cannot
know whether the PEs' ability to handle VPN routes has reached the
upper limit or not, so it needs the RD-ORF to control the number of
routes.
The operating mechanism of RD-ORF is similar to the description in
Section 6.1.
7. Security Considerations
A BGP speaker will maintain the RD-ORF entries in Adj-RIB-out, this
behavior consumes its memory and compute resources. To avoid the
excessive consumption of resources, [RFC5291] specifies that a BGP
speaker can only accept ORF entries transmitted by its interested
peers.
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8. IANA Considerations
This document defines a new Outbound Route Filter type - Route
Distinguisher Outbound Route Filter (RD-ORF). The code point is from
the "BGP Outbound Route Filtering (ORF) Types". It is recommended to
set the code point of RD-ORF to 66.
IANA is requested to allocate one code point for Source Address sub-
TLV for RD-ORF.
This document defines the following new RD-ORF sub-TLV types, which
should be reflected in the Source Address sub-TLV for RD-ORF Code
Point registry:
+----+-------------------------------------------------------------------+
|Type| Description |
+----+-------------------------------------------------------------------+
| 1 | Next hop Source Address sub-TLV |
+----+-------------------------------------------------------------------+
| 2 | Route Origin Community Source Address sub-TLV |
+----+-------------------------------------------------------------------+
9. Acknowledgement
Thanks Robert Raszuk, Jim Uttaro, Jakob Heitz, Jeff Tantsura, Rajiv
Asati, John E Drake and Gert Doering for their valuable comments on
this draft.
10. Normative References
[I-D.ietf-bess-evpn-inter-subnet-forwarding]
Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
Rabadan, "Integrated Routing and Bridging in EVPN", draft-
ietf-bess-evpn-inter-subnet-forwarding-09 (work in
progress), June 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[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>.
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[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5291] Chen, E. and Y. Rekhter, "Outbound Route Filtering
Capability for BGP-4", RFC 5291, DOI 10.17487/RFC5291,
August 2008, <https://www.rfc-editor.org/info/rfc5291>.
[RFC5292] Chen, E. and S. Sangli, "Address-Prefix-Based Outbound
Route Filter for BGP-4", RFC 5292, DOI 10.17487/RFC5292,
August 2008, <https://www.rfc-editor.org/info/rfc5292>.
[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, <https://www.rfc-editor.org/info/rfc7432>.
Authors' Addresses
Wei Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: wangw36@chinatelecom.cn
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: wangaj3@chinatelecom.cn
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Haibo Wang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing, Beijing 100095
China
Email: rainsword.wang@huawei.com
Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring MD 20904
United States of America
Phone: 301 502-1347
Email: gyan.s.mishra@verizon.com
Shunwan Zhuang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing, Beijing 100095
China
Email: zhuangshunwan@huawei.com
Jie Dong
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing, Beijing 100095
China
Email: jie.dong@huawei.com
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