Internet DRAFT - draft-wang-bess-center-rt5-for-common-prefix
draft-wang-bess-center-rt5-for-common-prefix
BESS WG Y. Wang
Internet-Draft ZTE Corporation
Intended status: Standards Track 21 March 2022
Expires: 22 September 2022
Centerlized EVPN Prefix Advertisement for Common Prefixes behind
Different CEs
draft-wang-bess-center-rt5-for-common-prefix-00
Abstract
In Section 5.8 of [I-D.wang-bess-evpn-arp-nd-synch-without-irb],
centerlized RT-5 advertisement are used for common prefixes behind
different CEs, This draft describes the requirements for such
scenarios. Then this draft reuse the procedures defined in
Section 6.2.2 of [I-D.wz-bess-evpn-vpws-as-vrf-ac] to support this
scenario.
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Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. ECMP for Centerlized RT-5 Advertisement . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Basic Control Plane Procedures . . . . . . . . . . . . . 5
3.1.1. Centerlized CE-BGP . . . . . . . . . . . . . . . . . 5
3.1.2. RT-2E Advertisement from PE1/PE2 to DGW1 . . . . . . 6
3.1.3. RT-5G Advertisement from DGW1 to PE1/PE2/PE3/DGW1' . 6
3.1.4. RT-2E Advertisement between PE1 and PE2 . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Normative References . . . . . . . . . . . . . . . . . . . . 7
7. Informative References . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
In Figure 1, Both R1 and R2 advertise their prefixes to DGW1
according to Section 5 of
[I-D.wang-bess-evpn-arp-nd-synch-without-irb]. Subnet SN1 can only
be reached through R1, so we say SN1 is R1's exlusive prefix. Then
subnet SN2 is R2's exlusive prefix, because SN2 can only be reached
throug R2. But subnet SN21 can be reached either through R1, or
through R2, thus we say SN21 is a common prefix of R1 and R2.
When there are both exlusive prefixes and common prefixes behind some
CEs, some special requirements should be considered, especially when
some of these CEs will not aware which prefixes are the common
prefixes. This draft describes the requirements and solutions
related to these scenarios .
1.1. ECMP for Centerlized RT-5 Advertisement
R1 and R2 both establish a single CE-BGP session with DGW1. These
CE-BGP session can be called the centerlized CE-BGP session.
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SN21 is a common prefix of R1 and R2, when R4 send traffic to a host
inside subnet SN21, DGW1' should load-balance that traffic between
PE1, PE2 and PE3.
+--------------------->----------------------+
| CE-BGP |
| PE3 |
| +----------+ |
| | +------+ | ------> | CE-BGP
R2 | | | | | RT-2R | SN21,SN2
+-------+ | | VPNx | | 20.2(MAC34) | NH=20.2
| | P3.1 | | | | MAC34 |
| ...................(20.9)| | |
| . | | +------+ | | DGW1'
SN2--| . | +----------+ +---|---------+
| . | ^ <---------- | V |
| . | | RT-2 RT-5 | +---------+ |
|(20.2) | | 20.2 SN21 | | VPNx | |
| . | | ESI34 GW-IP=20.2 | | |....R4
+---| . | | | |(z.z.z.z)| |
| | . | +----------+ ------> | | | |
| | . | | +------+ | RT-2R | +---------+ |
| | ...................(20.9)| | 20.2 | |
| | | P4.1 | | | | MAC34 +-------------+
| +-------+ | | | |
SN21 PE1 | | VPNx | | ------>
| R1 | | | | RT-2R
| +-------+ | | | | 10.2
| | | P1.1 | | | | MAC21
| | ...................(10.9)| | DGW1
| | . | | +------+ | +-------------+
| | . | +----------+ | |
+---| . | ^ <---------- | +---------+ |
| . | | RT-2 RT-5 | | | |
|(10.2) | | 10.2 SN21 | | VPNx | |
| . | | ESI21 GW-IP=10.2 | | |....R3
| . | | | |(z.z.z.z)| |
SN1--| . | +----------+ ------> | +---------+ |
| . | | +------+ | RT-2R | ^ |
| ...................(10.9)| | 10.2 | | |
| | P2.1 | | | | MAC21 +---|---------+
+-------+ | | VPNx | | |
| | | | | | CE-BGP
| | +------+ | | SN21,SN1
| +----------+ | NH=10.2
| PE2 |
| CE-BGP |
+--------------------->----------------------+
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Figure 1: Centerlized RT-5 for common CE-Prefixes
Note that we just use centerlized CE-BGP session to discover CE-
prefixes, but we still expect a distributed Layer 3 forwarding
framework.
1.2. Terminology
Most of the terminology used in this documents comes from [RFC7432]
and [RFC9136] except for the following:
* L3 EVI: An EVPN instance spanning the Provider Edge (PE) devices
participating in that EVPN which contains VRF ACs and maybe
contains IRB interfaces or IRC interfaces.
* CE-BGP: The BGP session between PE and CE. Note that CE-BGP route
doesn't have a RD or Route-Target.
* RMAC: Router's MAC, which is signaled in the Router's MAC extended
community.
* RT-2R: When a MAC/IP Advertisement Route is used in the context of
an IP-VRF, it is called as a RT-2R in this draft.
* RT-5E: An EVPN Prefix Advertisement Route with a non-reserved ESI.
* RT-5G: An EVPN Prefix Advertisement Route with a zero ESI and a
non-zero GW-IP.
* RT-5L: An EVPN Prefix Advertisement Route with both zero ESI and
zero GW-IP, but a valid MPLS label.
* Internal Remote PE: When PEx is called as an EVPN route ERy's
internal remote PE, that is saying that, PEx is on the ES which is
identified by ERy's ESI field. When ERy's SOI is not zero, that is
aslo saying that PEx has been attached to the ethernet tag which is
identified by the <ESI, SOI>.
* External Remote PE: When PEx is called as an EVPN route ERy's
external remote PE, that is saying that, PEx is not on the ES which
is identified by ERy's ESI field. When ERy's SOI is not zero, PEx
may aslo be a PE which has not been attached to the ethernet tag
which is identified by the <ESI, SOI>.
* CE-Prefix: When an IP prefix can be reached through CEx from PEy,
that IP prefix is called as PEy's CE-prefix behind CEx in this
draft. PEy's CE-prefix behind CEx is also called as PEy's CE-
prefix for short in this draft.
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* Common CE-Prefix: When an CE-Prefix can be reached through either
CEy or CEz from PEy, in this draft, it is called as a common CE-
Prefix of CEy and CEz,from the viewpoint of PEy.
* Exclusive CE-Prefix: When an CE-Prefix of PEy can be reached
through CEy, and it can't be reached through other CEs of PEy, it
is called as an exlusive CE-Prefix of CEy, from the viewpoint of
PEy.
* SNGW: Sub-Net-specific Gate Way IP address, the SNGW of a subnet
is an IP address which is used by the hosts of that subnet to be
the nexthop of the default route of these host.
* Overlay nexthop : The CE-Prefix's nexthop IP address which is in
the address-space of the L3 EVI.
* Original Overlay nexthop : The overlay nexthop which is advertised
by the CE through a PE-CE route protocol.
2. Requirements
Before advertise SN1/SN2/SN21 to DGWs, R1 and R2 don't have to know
which prefix is their common prefix, and which prefix is their
exclusive prefix.
3. Solution
3.1. Basic Control Plane Procedures
3.1.1. Centerlized CE-BGP
The CE-BGP session between R1 and DGW1 is established between 10.2
and z.z.z.z. The IP address 10.2 is called the uplink interface
address of R1 in this document. The IP address z.z.z.z is called the
centerlized loopback address of VPNx in this document. The IP
address 10.9 is called the downlink VRF-interface address of PE1/PE2
in this document.
R1 advertises a BGP route for a prefix (say "SN21") behind it to DGW1
via that CE-BGP session. The nexthop for SN21 is R1's uplink
interface address (say 10.2).
R2 advertises a BGP route for a prefix (say "SN21") behind it to
DGW1' via that CE-BGP session. The nexthop for SN21 is R2's uplink
interface address (say 20.2).
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Note that the data packets from R1(R2) to the centerlized loopback
address may be routed following the default route on R1(R2). Thus
DGW1 doesn't need to use the CE-BGP session to advertise prefixes of
VPNx to R1(R2).
3.1.2. RT-2E Advertisement from PE1/PE2 to DGW1
When PE1 and PE2 learns the ARP entry of 10.2, it advertises a RT-2R
route to DGW1 (and DGW1').
When PE1 and PE3 learns the ARP entry of 20.2, it advertises a RT-2R
route to DGW1 (and DGW1').
3.1.3. RT-5G Advertisement from DGW1 to PE1/PE2/PE3/DGW1'
When DGW1 receives the SN21 from the CE-BGP session. The nexthop for
SN21 is 10.2. So DGW1 advertises a RT-5G route to PE1/PE2/PE3 for
SN21. The GW-IP value of the RT-5G route for SN21 is 10.2.
When DGW1' receives the SN21 from the CE-BGP session. The nexthop
for SN21 is 20.2. So DGW1 advertises a RT-5G route to PE1/PE2/PE3
for SN21. The GW-IP value of the RT-5G route for SN21 is 20.2.
DGW1 and DGW1' may be the same device, in such case DGW1 should use
the ADD-PATH of [RFC7911] to advertise two GW-IPs for the same
prefixe SN21.
Note that when other PEs receive these RT-5 route for SN21, the ECMP
behavior is already defined in Section 4.1 of [RFC9136] as the
following:
* Based on the BD-10 Route Target in DGW1 and DGW2, the IP
Prefix route is also imported, and SN1/24 is added to the IP-
VRF with Overlay Index IP2 pointing at the local BD-10. In
this example, it is assumed that the RT-5 from NVE2 is
preferred over the RT-5 from NVE3. If both routes were
equally preferable and ECMP enabled, SN1/24 would also be
added to the routing table with Overlay Index IP3.
Figure 2: ECMP for GW-IP based RT-5
3.1.4. RT-2E Advertisement between PE1 and PE2
The RT-2R routes advertisement between PE1 and PE2 is used to sync
subnet 10.0's ARP entries to each other in order to avoid ARP
missing. The ESI Value of these two RT-2R routes is ESI21.
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The RT-2R routes advertisement between PE1 and PE3 is used to sync
subnet 20.0's ARP entries to each other in order to avoid ARP
missing. The ESI Value of these two RT-2R routes is ESI34.
4. Security Considerations
TBD.
5. IANA Considerations
There is no IANA consideration needed.
6. Normative References
[I-D.wang-bess-evpn-arp-nd-synch-without-irb]
Wang, Y. and Z. Zhang, "ARP/ND Synching And IP Aliasing
without IRB", Work in Progress, Internet-Draft, draft-
wang-bess-evpn-arp-nd-synch-without-irb-08, 1 September
2021, <https://datatracker.ietf.org/doc/html/draft-wang-
bess-evpn-arp-nd-synch-without-irb-08>.
[I-D.wz-bess-evpn-vpws-as-vrf-ac]
Wang, Y. and Z. Zhang, "EVPN VPWS as VRF Attachment
Circuit", Work in Progress, Internet-Draft, draft-wz-bess-
evpn-vpws-as-vrf-ac-02, 28 August 2021,
<https://datatracker.ietf.org/doc/html/draft-wz-bess-evpn-
vpws-as-vrf-ac-02>.
[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>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
Rabadan, "Virtual Private Wire Service Support in Ethernet
VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
<https://www.rfc-editor.org/info/rfc8214>.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
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[RFC9135] Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
Rabadan, "Integrated Routing and Bridging in Ethernet VPN
(EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
<https://www.rfc-editor.org/info/rfc9135>.
[RFC9136] Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
(EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
<https://www.rfc-editor.org/info/rfc9136>.
7. Informative References
[I-D.sajassi-bess-evpn-ip-aliasing]
Sajassi, A., Badoni, G., Warade, P., Pasupula, S.,
Krattiger, L., Drake, J., and J. Rabadan, "EVPN Support
for L3 Fast Convergence and Aliasing/Backup Path", Work in
Progress, Internet-Draft, draft-sajassi-bess-evpn-ip-
aliasing-04, 7 March 2022,
<https://datatracker.ietf.org/doc/html/draft-sajassi-bess-
evpn-ip-aliasing-04>.
Author's Address
Yubao Wang
ZTE Corporation
No. 68 of Zijinghua Road, Yuhuatai Distinct
Nanjing
China
Email: wang.yubao2@zte.com.cn
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