Internet DRAFT - draft-zzhang-lsr-anycast-affiliation
draft-zzhang-lsr-anycast-affiliation
lsr Z. Zhang
Internet-Draft Juniper Networks
Intended status: Standards Track 7 March 2022
Expires: 8 September 2022
Anycast Affiliation Advertisement
draft-zzhang-lsr-anycast-affiliation-00
Abstract
This document specifies the advertisement of addresses affiliated
with an anycast address in ISIS/OSPF/BGP, and describes one example
use of such advertisement in VxLAN interconnect with EVPN.
Status of This Memo
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This Internet-Draft will expire on 8 September 2022.
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Table of Contents
1. Background . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specifications . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. ISIS Encoding . . . . . . . . . . . . . . . . . . . . . . 4
2.2. OSPF Encoding . . . . . . . . . . . . . . . . . . . . . . 4
2.3. BGP Encoding . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Background
[I-D.boutros-bess-vxlan-evpn] describes how Ethernet VPN (EVPN)
[RFC7432] can be used to interconnect VXLAN/NVGRE networks over an
MPLS/IP network. In the following diagram copied from that draft, a
pair of gateways PE1/PE2, which are both VXLAN/NVGRE VTEPs and EVPN
PEs, connect a VXLAN/NVGRE site to the EVPN Data Center Interconnect
(DCI).
+--------------+
| |
+---------+ +----+ MPLS +----+ +---------+
+-----+ | |---|PE1 | |PE3 |--| | +-----+
|VTEP1|--| | +----+ +----+ | |--|VTEP3|
+-----+ | VXLAN | +----+ +----+ | VXLAN | +-----+
+-----+ | |---|PE2 | |PE4 |--| | +-----+
|VTEP2|--| | +----+Backbone+----+ | |--|VTEP4|
+-----+ +---------+ +--------------+ +---------+ +-----+
|<--- Underlay IGP ---->|<-Overlay BGP->|<--- Underlay IGP --->| CP
|<----- VXLAN --------->|<EVPN/PBB-EVPN>|<------ VXLAN ------->| DP
|<----MPLS----->|
Legend: CP = Control Plane View DP = Data Plane View
PE1/PE2 use a common anycast address as the source address of VXLAN/
NVGRE packets towards other VXLAN/NVGRE VTEPs. This serves two
purposes as stated in [I-D.boutros-bess-vxlan-evpn]:
* It prevents any flip/flopping in the forwarding tables for the
MAC-to-VTEP associations
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* It enables load-balancing via ECMP for DCI traffic among the
multi-homed PEs
Notice that load-balancing is only possible with ECMP - a VTEP uses
the anycast address as the destination address in its VXLAN/NVGRE
packets towards the DCI, and ECMP-based load-balancing can happen on
any router from the source VTEP towards PE1/PE2.
However, if the source VTEP knows that PE1/PE2's specific non-anycast
address that are associated with the anycast address, it can load-
balance traffic using those specific addresses, even when there is no
ECMP to PE1/PE2.
There are two ways for a VTEP to learn the affiliation of an address
to an anycast address:
* Provisioning on the VTEPs - statically or from a controller
* Dynamic advertisement via IGP/BGP from the anycast address
"owners" (PE1/PE2)
This document specifies the dynamic advertisement of anycast address
affiliation via IGP/BGP, which can actually serve other general
purposes as well.
Even though if a node advertises anycast and non-anycast local
addresses using existing methods (e.g. with ISIS's N-bit) then others
can derive that those addresses are owned by the same advertiser, it
is desired to explicitly announce the non-anycast addresses
affiliated with an anycast address for the following reasons:
* Just because a node advertises two addresses A and B it does not
mean A and B are exchangeable when another node needs to send
traffic to it. Explicit association should be known for the
source node to choose an "alias" address to send traffic.
* The affiliation may have to be one-way - if a node needs to send
traffic to an anycast address it can use the affiliated non-
anycast addresses (or even a transit node may choose to change the
destination address from anycast to an affiliated address) but the
other way may not be desired (or allowed at all in the case of
transit node changing destination address - otherwise loops could
happen).
* A node may have different anycast addresses and it may be
necessary to associate different non-anycast addresses to
different non-anycast addresses.
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* A node may also withdraw the affiliation advertisement even when
all the relevant addresses are still reachable. In that case,
only the affiliation is withdrawn, not the reachability.
For example, in the above VXLAN-EVPN interconnect scenario, if PE2
looses all its EVPN peers, it may withdraw anycast address
affiliation advertisement and then the VTEPs can stop sending traffic
to it.
2. Specifications
2.1. ISIS Encoding
A new "Anycast Affiliation sub-TLV" is defined for ISIS extended
Reachability TLVs [RFC7794]. It MAY be advertised with an anycast
host prefix. Its value part includes a list of affiliated local
addresses. The number of affiliated addresses is determined from the
length of the sub-TLV.
2.2. OSPF Encoding
A new "Anycast Affiliation sub-TLV" is defined for OSPFv2 Extended
Prefix TLVs [RFC7684]. It MAY be advertised with an anycast host
prefix. Its value part includes a list of affiliated local
addresses. The number of affiliated addresses is determined from the
length of the sub-TLV.
A new "Anycast Affiliation sub-TLV" is defined for OSPFv3 Intra-Area-
Prefix TLV and Inter-Area-Prefix TLV [RFC8362]. It MAY be advertised
with an anycast host prefix. Its value part includes a list of
affiliated local addresses. The number of affiliated addresses is
determined from the length of the sub-TLV.
2.3. BGP Encoding
IPv4 (or IPv6) Address Specific Extended Communities with an "Anycast
Affiliation" sub-type (or type in case of IPv6) MAY be attached to
the NLRI of an anycast host prefix, one such extended community for
each affiliated address. The Global Administrator field of the
extended community is set to the affiliated address, and the Local
Administrator field is set to 0.
3. Security Considerations
To be provided.
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4. IANA Considerations
IANA is requested to allocate the following:
* A new sub-TLV type for "Anycast Affiliation" from the ISIS "Sub-
TLVs for TLVs 135, 235, 236, and 237" registry [RFC7794]
* A new sub-TLV type for "Anycast Affiliation" from the OSPFv2
Extended Prefix TLV Sub-TLVs" registry [RFC7684]
* A new sub-TLV type for "Anycast Affiliation" from the OSPFv3
Extended-LSA sub-TLV registry [RFC8362]
* A new sub-type for "Anycast Affiliation" from the Transitive IPv4-
Address-Specific Extended Community Sub-Types registry and Non-
Transitive IPv4-Address-Specific Extended Community Sub-Types
registry
* A new type for "Anycast Affiliation" from the Transitive IPv6-
Address-Specific Extended Community Types registry and Non-
Transitive IPv6-Address-Specific Extended Community Types registry
5. Acknowledgements
The author thanks Shraddha Hegde for her inputs and comments.
6. References
6.1. Normative References
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
6.2. Informative References
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[I-D.boutros-bess-vxlan-evpn]
Boutros, S., Sajassi, A., Salam, S., Cai, D., Thoria, S.,
Singh, T., Drake, J., and J. Tantsura, "VXLAN DCI Using
EVPN", Work in Progress, Internet-Draft, draft-boutros-
bess-vxlan-evpn-02, 21 October 2016,
<https://www.ietf.org/archive/id/draft-boutros-bess-vxlan-
evpn-02.txt>.
[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>.
Author's Address
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
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