L2VPN Workgroup J. Rabadan
Internet Draft W. Henderickx
S. Palislamovic
Intended status: Standards Track Alcatel-Lucent
J. Drake F. Balus
Juniper Nuage Networks
A. Sajassi A. Isaac
Cisco Bloomberg
Expires: August 1, 2015 January 28, 2015
IP Prefix Advertisement in EVPN
draft-ietf-bess-evpn-prefix-advertisement-00
Abstract
EVPN provides a flexible control plane that allows intra-subnet
connectivity in an IP/MPLS and/or an NVO-based network. In NVO
networks, there is also a need for a dynamic and efficient inter-
subnet connectivity across Tenant Systems and End Devices that can be
physical or virtual and may not support their own routing protocols.
This document defines a new EVPN route type for the advertisement of
IP Prefixes and explains some use-case examples where this new route-
type is used.
Status of this Memo
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This Internet-Draft will expire on August 1, 2015.
Copyright Notice
Copyright (c) 2015 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
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction and problem statement . . . . . . . . . . . . . . 3
2.1 Inter-subnet connectivity requirements in Data Centers . . . 4
2.2 The requirement for a new EVPN route type . . . . . . . . . 6
3. The BGP EVPN IP Prefix route . . . . . . . . . . . . . . . . . 7
3.1 IP Prefix Route encoding . . . . . . . . . . . . . . . . . . 8
4. Benefits of using the EVPN IP Prefix route . . . . . . . . . . 10
5. IP Prefix next-hop use-cases . . . . . . . . . . . . . . . . . 11
5.1 TS IP address next-hop use-case . . . . . . . . . . . . . . 11
5.2 Floating IP next-hop use-case . . . . . . . . . . . . . . . 14
5.3 ESI next-hop ("Bump in the wire") use-case . . . . . . . . . 16
5.4 IRB forwarding on NVEs for Subnets (IP-VRF-to-IP-VRF) . . . 18
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7. Conventions used in this document . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 22
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1 Normative References . . . . . . . . . . . . . . . . . . . 22
10.2 Informative References . . . . . . . . . . . . . . . . . . 22
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
12. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 22
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1. Terminology
GW IP: Gateway IP Address
IPL: IP address length
IRB: Integrated Routing and Bridging interface
ML: MAC address length
NVE: Network Virtualization Edge
TS: Tenant System
VA: Virtual Appliance
RT-2: EVPN route type 2, i.e. MAC/IP advertisement route
RT-5: EVPN route type 5, i.e. IP Prefix route
Overlay next-hop: object used in the IP Prefix route, as described in
this document. It can be an IP address in the tenant space or an ESI,
and identifies the next-hop yielded by the IP route lookup at the
routing context importing the route. An overlay next-hop always needs
a recursive route resolution on the NVE receiving the IP Prefix
route, so that the NVE knows to which egress NVE to forward the
packets.
Underlay next-hop: IP address sent by BGP along with any EVPN route,
i.e. BGP next-hop. It identifies the NVE sending the route and it is
used at the receiving NVE as the VXLAN destination VTEP or NVGRE
destination end-point.
2. Introduction and problem statement
Inter-subnet connectivity is required for certain tenants within the
Data Center. [EVPN-INTERSUBNET] defines some fairly common inter-
subnet forwarding scenarios where TSes can exchange packets with TSes
located in remote subnets. In order to meet this requirement,
[EVPN-INTERSUBNET] describes how MAC/IPs encoded in TS RT-2 routes
are not only used to populate MAC-VRF and overlay ARP tables, but
also IP-VRF tables with the encoded TS host routes (/32 or /128). In
some cases, EVPN may advertise IP Prefixes and therefore provide
aggregation in the IP-VRF tables, as opposed to program individual
host routes. This document complements the scenarios described in
[EVPN-INTERSUBNET] and defines how EVPN may be used to advertise IP
Prefixes.
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Section 2.1 describes the inter-subnet connectivity requirements in
Data Centers. Section 2.2 explains why a new EVPN route type is
required for IP Prefix advertisements. Once the need for a new EVPN
route type is justified, sections 3, 4 and 5 will describe this route
type and how it is used in some specific use cases.
2.1 Inter-subnet connectivity requirements in Data Centers
[EVPN] is used as the control plane for a Network Virtualization
Overlay (NVO3) solution in Data Centers (DC), where Network
Virtualization Edge (NVE) devices can be located in Hypervisors or
TORs, as described in [EVPN-OVERLAYS].
If we use the term Tenant System (TS) to designate a physical or
virtual system identified by MAC and IP addresses, and connected to
an EVPN instance, the following considerations apply:
o The Tenant Systems may be Virtual Machines (VMs) that generate
traffic from their own MAC and IP.
o The Tenant Systems may be Virtual Appliance entities (VAs) that
forward traffic to/from IP addresses of different End Devices
seating behind them.
o These VAs can be firewalls, load balancers, NAT devices, other
appliances or virtual gateways with virtual routing instances.
o These VAs do not have their own routing protocols and hence
rely on the EVPN NVEs to advertise the routes on their behalf.
o In all these cases, the VA will forward traffic to the Data
Center using its own source MAC but the source IP will be the
one associated to the End Device seating behind or a
translated IP address (part of a public NAT pool) if the VA is
performing NAT.
o Note that the same IP address could exist behind two of these
TS. One example of this would be certain appliance resiliency
mechanisms, where a virtual IP or floating IP can be owned by
one of the two VAs running the resiliency protocol (the master
VA). VRRP is one particular example of this. Another example
is multi-homed subnets, i.e. the same subnet is connected to
two VAs.
o Although these VAs provide IP connectivity to VMs and subnets
behind them, they do not always have their own IP interface
connected to the EVPN NVE, e.g. layer-2 firewalls are examples
of VAs not supporting IP interfaces.
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The following figure illustrates some of the examples described
above.
NVE1
+-----------+
TS1(VM)--|(MAC-VRF10)|-----+
IP1/M1 +-----------+ | DGW1
+---------+ +-------------+
| |----|(MAC-VRF10) |
SN1---+ NVE2 | | | IRB1\ |
| +-----------+ | | | (IP-VRF)|---+
SN2---TS2(VA)--|(MAC-VRF10)|-| | +-------------+ _|_
| IP2/M2 +-----------+ | VXLAN/ | ( )
IP4---+ <-+ | nvGRE | DGW2 ( WAN )
| | | +-------------+ (___)
vIP23 (floating) | |----|(MAC-VRF10) | |
| +---------+ | IRB2\ | |
SN1---+ <-+ NVE3 | | | | (IP-VRF)|---+
| IP3/M3 +-----------+ | | | +-------------+
SN3---TS3(VA)--|(MAC-VRF10)|---+ | |
| +-----------+ | |
IP5---+ | |
| |
NVE4 | | NVE5 +--SN5
+---------------------+ | | +-----------+ |
IP6------|(MAC-VRF1) | | +-|(MAC-VRF10)|--TS4(VA)--SN6
| \ | | +-----------+ |
| (IP-VRF) |--+ ESI4 +--SN7
| / \IRB3 |
|---|(MAC-VRF2)(MAC-VRF10)|
SN4| +---------------------+
Figure 1 DC inter-subnet use-cases
Where:
NVE1, NVE2, NVE3, NVE4, NVE5, DGW1 and DGW2 share the same EVI for a
particular tenant. EVI-10 is comprised of the collection of MAC-VRF10
instances defined in all the NVEs. All the hosts connected to EVI-10
belong to the same IP subnet. The hosts connected to EVI-10 are
listed below:
o TS1 is a VM that generates/receives traffic from/to IP1, where
IP1 belongs to the EVI-10 subnet.
o TS2 and TS3 are Virtual Appliances (VA) that generate/receive
traffic from/to the subnets and hosts seating behind them
(SN1, SN2, SN3, IP4 and IP5). Their IP addresses (IP2 and IP3)
belong to the EVI-10 subnet and they can also generate/receive
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traffic. When these VAs receive packets destined to their own
MAC addresses (M2 and M3) they will route the packets to the
proper subnet or host. These VAs do not support routing
protocols to advertise the subnets connected to them and can
move to a different server and NVE when the Cloud Management
System decides to do so. These VAs may also support redundancy
mechanisms for some subnets, similar to VRRP, where a floating
IP is owned by the master VA and only the master VA forwards
traffic to a given subnet. E.g.: vIP23 in figure 1 is a
floating IP that can be owned by TS2 or TS3 depending on who
the master is. Only the master will forward traffic to SN1.
o Integrated Routing and Bridging interfaces IRB1, IRB2 and IRB3
have their own IP addresses that belong to the EVI-10 subnet
too. These IRB interfaces connect the EVI-10 subnet to Virtual
Routing and Forwarding (VRF) instances that can route the
traffic to other connected subnets for the same tenant (within
the DC or at the other end of the WAN).
o TS4 is a layer-2 VA that provides connectivity to subnets SN5,
SN6 and SN7, but does not have an IP address itself in the
EVI-10. TS4 is connected to a physical port on NVE5 assigned
to Ethernet Segment Identifier 4.
All the above DC use cases require inter-subnet forwarding and
therefore the individual host routes and subnets:
a) MUST be advertised from the NVEs (since VAs and VMs do not run
routing protocols) and
b) MAY be associated to an overlay next-hop that can be a VA IP
address, a floating IP address or an ESI.
2.2 The requirement for a new EVPN route type
[EVPN] defines a MAC/IP route (also referred as RT-2) where a MAC
address can be advertised together with an IP address length (IPL)
and IP address (IP). While a variable IPL might have been used to
indicate the presence of an IP prefix in a route type 2, there are
several specific use cases in which using this route type to deliver
IP Prefixes is not suitable.
One example of such use cases is the "floating IP" example described
in section 2.1. In this example we need to decouple the advertisement
of the prefixes from the advertisement of the floating IP (vIP23 in
figure 1) and MAC associated to it, otherwise the solution gets
highly inefficient and does not scale.
E.g.: if we are advertising 1k prefixes from M2 (using RT-2) and the
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floating IP owner changes from M2 to M3, we would need to withdraw 1k
routes from M2 and re-advertise 1k routes from M3. However if we use
a separate route type, we can advertise the 1k routes associated to
the floating IP address (vIP23) and only one RT-2 for advertising the
ownership of the floating IP, i.e. vIP23 and M2 in the route type 2.
When the floating IP owner changes from M2 to M3, a single RT-2
withdraw/update is required to indicate the change. The remote DGW
will not change any of the 1k prefixes associated to vIP23, but will
only update the ARP resolution entry for vIP23 (now pointing at M3).
Other reasons to decouple the IP Prefix advertisement from the MAC/IP
route are listed below:
o Clean identification, operation of troubleshooting of IP
Prefixes, not subject to interpretation and independent of the
IPL and the IP value. E.g.: a default IP route 0.0.0.0/0 must
always be easily and clearly distinguished from the absence of
IP information.
o MAC address information must not be compared by BGP when
selecting two IP Prefix routes. If IP Prefixes were to be
advertised using MAC/IP routes, the MAC information would
always be present and part of the route key.
o IP Prefix routes must not be subject to MAC/IP route
procedures such as MAC mobility or aliasing. Prefixes
advertised from two different ESIs do not mean mobility; MACs
advertised from two different ESIs do mean mobility. Similarly
load balancing for IP prefixes is achieved through IP
mechanisms such as ECMP, and not through MAC route mechanisms
such as aliasing.
o NVEs that do not require processing IP Prefixes must have an
easy way to identify an update with an IP Prefix and ignore
it, rather than processing the MAC/IP route to find out only
later that it carries a Prefix that must be ignored.
The following sections describe how EVPN is extended with a new route
type for the advertisement of IP prefixes and how this route is used
to address the current and future inter-subnet connectivity
requirements existing in the Data Center.
3. The BGP EVPN IP Prefix route
The current BGP EVPN NLRI as defined in [EVPN] is shown below:
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+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
Where the route type field can contain one of the following specific
values:
+ 1 - Ethernet Auto-Discovery (A-D) route
+ 2 - MAC/IP advertisement route
+ 3 - Inclusive Multicast Route
+ 4 - Ethernet Segment Route
This document defines an additional route type that will be used for
the advertisement of IP Prefixes:
+ 5 - IP Prefix Route
The support for this new route type is OPTIONAL.
Since this new route type is OPTIONAL, an implementation not
supporting it MUST ignore the route, based on the unknown route type
value.
The detailed encoding of this route and associated procedures are
described in the following sections.
3.1 IP Prefix Route encoding
An IP Prefix advertisement route NLRI consists of the following
fields:
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+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
|Ethernet Segment Identifier (10 octets)|
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| IP Prefix Length (1 octet) |
+---------------------------------------+
| IP Prefix (4 or 16 octets) |
+---------------------------------------+
| GW IP Address (4 or 16 octets) |
+---------------------------------------+
| MPLS Label (3 octets) |
+---------------------------------------+
Where:
o RD, Ethernet Tag ID and MPLS Label fields will be used as
defined in [EVPN] and [EVPN-OVERLAYS].
o The Ethernet Segment Identifier will be a non-zero 10-byte
identifier if the ESI is used as an overlay next-hop. It will
be zero otherwise.
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 IP Prefix will be a 32 or 128-bit field (ipv4 or ipv6).
o The GW IP (Gateway IP Address) will be a 32 or 128-bit field
(ipv4 or ipv6), and will encode the overlay IP next-hop for
the IP Prefixes. The GW IP field can be zero if it is not used
as an overlay next-hop.
o The total route length will indicate the type of prefix (ipv4
or ipv6) and the type of GW IP address (ipv4 or ipv6). Note
that the IP Prefix + the GW IP should have a length of either
64 or 256 bits, but never 160 bits (ipv4 and ipv6 mixed values
are not allowed).
The Eth-Tag ID, IP Prefix Length and IP Prefix will be part of the
route key used by BGP to compare routes. The rest of the fields will
not be part of the route key.
The route will contain a single overlay next-hop at most, i.e. if the
ESI field is different from zero, the GW IP field will be zero, and
vice versa. The following table shows the different inter-subnet use-
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cases described in this document and the corresponding coding of the
overlay next-hop in the route type 5 (RT-5). The IP-VRF-to-IP-VRF or
IRB forwarding on NVEs case is a special use-case, where there is no
need for overlay next-hop, since the actual next-hop is given by the
BGP next-hop. When an overlay next-hop is present in the RT-5, the
receiving NVE will need to perform a recursive route resolution to
find out to which egress NVE to forward the packets.
+----------------------------+----------------------------------+
| Use-case | Next-hop in the RT-5 BGP update |
+----------------------------+----------------------------------+
| TS IP address | GW IP Address |
| Floating IP address | GW IP Address |
| "Bump in the wire" | ESI |
| IP-VRF-to-IP-VRF | BGP next-hop |
+----------------------------+----------------------------------+
4. Benefits of using the EVPN IP Prefix route
This section clarifies the different functions accomplished by the
EVPN RT-2 and RT-5 routes, and provides a list of benefits derived
from using a separate route type for the advertisement of IP Prefixes
in EVPN.
[EVPN] describes the content of the BGP EVPN RT-2 specific NLRI, i.e.
MAC/IP Advertisement Route, where the IP address length (IPL) and IP
address (IP) of a specific advertised MAC are encoded. The subject of
the MAC advertisement route is the MAC address (M) and MAC address
length (ML) encoded in the route. The MAC mobility and other complex
procedures are defined around that MAC address. The IP address
information carries the host IP address required for the ARP
resolution of the MAC according to [EVPN] and the host route to be
programmed in the IP-VRF [EVPN-INTERSUBNET].
The BGP EVPN route type 5 defined in this document, i.e. IP Prefix
Advertisement route, decouples the advertisement of IP prefixes from
the advertisement of any MAC address related to it. This brings some
major benefits to NVO-based networks where certain inter-subnet
forwarding scenarios are required. Some of those benefits are:
a) Upon receiving a route type 2 or type 5, an egress NVE can easily
distinguish MACs and IPs from IP Prefixes. E.g. an IP prefix with
IPL=32 being advertised from two different ingress NVEs (as RT-5)
can be identified as such and be imported in the designated
routing context as two ECMP routes, as opposed to two MACs
competing for the same IP.
b) Similarly, upon receiving a route, an ingress NVE not supporting
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processing of IP Prefixes can easily ignore the update, based on
the route type.
c) A MAC route includes the ML, M, IPL and IP in the route key that
is used by BGP to compare routes, whereas for IP Prefix routes,
only IPL and IP (as well as Ethernet Tag ID) are part of the route
key. Advertised IP Prefixes are imported into the designated
routing context, where there is no MAC information associated to
IP routes. In the example illustrated in figure 1, subnet SN1
should be advertised by NVE2 and NVE3 and interpreted by DGW1 as
the same route coming from two different next-hops, regardless of
the MAC address associated to TS2 or TS3. This is easily
accomplished in the RT-5 by including only the IP information in
the route key.
d) By decoupling the MAC from the IP Prefix advertisement procedures,
we can leave the IP Prefix advertisements out of the MAC mobility
procedures defined in [EVPN] for MACs. In addition, this allows us
to have an indirection mechanism for IP Prefixes advertised from a
MAC/IP that can move between hypervisors. E.g. if there are 1,000
prefixes seating behind TS2 (figure 1), NVE2 will advertise all
those prefixes in RT-5 routes associated to the next-hop IP2.
Should TS2 move to a different NVE, a single MAC advertisement
route withdraw for the M2/IP2 route from NVE2 will invalidate the
1,000 prefixes, as opposed to have to wait for each individual
prefix to be withdrawn. This may be easily accomplished by using
IP Prefix routes that are not tied to a MAC address, and use a
different MAC/IP route to advertise the location and resolution of
the overlay next-hop to a MAC address.
5. IP Prefix next-hop use-cases
The IP Prefix route can use a GW IP or an ESI as an overlay next-hop
as well as no overlay next-hop whatsoever. This section describes
some use-cases for these next-hop types.
5.1 TS IP address next-hop use-case
The following figure illustrates an example of inter-subnet
forwarding for subnets seating behind Virtual Appliances (on TS2 and
TS3).
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SN1---+ NVE2 DGW1
| +-----------+ +---------+ +-------------+
SN2---TS2(VA)--|(MAC-VRF10)|-| |----|(MAC-VRF10) |
| IP2/M2 +-----------+ | | | IRB1\ |
IP4---+ | | | (IP-VRF)|---+
| | +-------------+ _|_
| VXLAN/ | ( )
| nvGRE | DGW2 ( WAN )
SN1---+ NVE3 | | +-------------+ (___)
| IP3/M3 +-----------+ | |----|(MAC-VRF10) | |
SN3---TS3(VA)--|(MAC-VRF10)|-| | | IRB2\ | |
| +-----------+ +---------+ | (IP-VRF)|---+
IP5---+ +-------------+
Figure 2 TS IP address use-case
An example of inter-subnet forwarding between subnet SN1/24 and a
subnet seating in the WAN is described below. NVE2, NVE3, DGW1 and
DGW2 are running BGP EVPN. TS2 and TS3 do not support routing
protocols, only a static route to forward the traffic to the WAN.
(1) NVE2 advertises the following BGP routes on behalf of TS2:
o Route type 2 (MAC/IP route) containing: ML=48, M=M2, IPL=32,
IP=IP2 and [RFC5512] BGP Encapsulation Extended Community with
Tunnel-type= VXLAN or NVGRE.
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=0, GW IP address=IP2 (and BGP Encapsulation Extended
Community).
(2) NVE3 advertises the following BGP routes on behalf of TS3:
o Route type 2 (MAC/IP route) containing: ML=48, M=M3, IPL=32,
IP=IP3 (and BGP Encapsulation Extended Community).
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=0, GW IP address=IP3 (and BGP Encapsulation Extended
Community).
(3) DGW1 and DGW2 import both received routes based on the
route-targets:
o Based on the MAC-VRF10 route-target in DGW1 and DGW2, the
MAC/IP route is imported and M2 is added to the MAC-VRF10
along with its corresponding tunnel information. For instance,
if VXLAN is used, the VTEP will be derived from the MAC/IP
route BGP next-hop (underlay next-hop) and VNI from the
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Ethernet Tag or MPLS fields. IP2 - M2 is added to the ARP
table.
o Based on the MAC-VRF10 route-target in DGW1 and DGW2, the IP
Prefix route is also imported and SN1/24 is added to the
designated routing context with next-hop IP2 pointing at the
local MAC-VRF10. Should ECMP be enabled in the routing
context, SN1/24 would also be added to the routing table with
next-hop IP3.
(4) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table and next-hop=IP2 is found. Since IP2 is an
overlay next-hop a recursive route resolution is required for
IP2.
o IP2 is resolved to M2 in the ARP table, and M2 is resolved to
the tunnel information given by the MAC FIB (remote VTEP and
VNI for the VXLAN case).
o The IP packet destined to IPx is encapsulated with:
. Source inner MAC = IRB1 MAC
. Destination inner MAC = M2
. Tunnel information provided by the MAC-VRF (VNI, VTEP IPs
and MACs for the VXLAN case)
(5) When the packet arrives at NVE2:
o Based on the tunnel information (VNI for the VXLAN case), the
MAC-VRF10 context is identified for a MAC lookup.
o Encapsulation is stripped-off and based on a MAC lookup
(assuming MAC forwarding on the egress NVE), the packet is
forwarded to TS2, where it will be properly routed.
(6) Should TS2 move from NVE2 to NVE3, MAC Mobility procedures will
be applied to the MAC route IP2/M2, as defined in [EVPN]. Route type
5 prefixes are not subject to MAC mobility procedures, hence no
changes in the DGW VRF routing table will occur for TS2 mobility,
i.e. all the prefixes will still be pointing at IP2 as next-hop.
There is an indirection for e.g. SN1/24, which still points at
next-hop IP2 in the routing table, but IP2 will be simply resolved to
a different tunnel, based on the outcome of the MAC mobility
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procedures for the MAC/IP route IP2/M2.
Note that in the opposite direction, TS2 will send traffic based on
its static-route next-hop information (IRB1 and/or IRB2), and regular
EVPN procedures will be applied.
5.2 Floating IP next-hop use-case
Sometimes Tenant Systems (TS) work in active/standby mode where an
upstream floating IP - owned by the active TS - is used as the
next-hop to get to some subnets behind. This redundancy mode, already
introduced in section 2.1 and 2.2, is illustrated in Figure 3.
NVE2 DGW1
+-----------+ +---------+ +-------------+
+---TS2(VA)--|(MAC-VRF10)|-| |----|(MAC-VRF10) |
| IP2/M2 +-----------+ | | | IRB1\ |
| <-+ | | | (IP-VRF)|---+
| | | | +-------------+ _|_
SN1 vIP23 (floating) | VXLAN/ | ( )
| | | nvGRE | DGW2 ( WAN )
| <-+ NVE3 | | +-------------+ (___)
| IP3/M3 +-----------+ | |----|(MAC-VRF10) | |
+---TS3(VA)--|(MAC-VRF10)|-| | | IRB2\ | |
+-----------+ +---------+ | (IP-VRF)|---+
+-------------+
Figure 3 Floating IP next-hop for redundant TS
In this example, assuming TS2 is the active TS and owns IP23:
(1) NVE2 advertises the following BGP routes for TS2:
o Route type 2 (MAC/IP route) containing: ML=48, M=M2, IPL=32,
IP=IP23 (and BGP Encapsulation Extended Community).
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=0, GW IP address=IP23 (and BGP Encapsulation Extended
Community).
(2) NVE3 advertises the following BGP routes for TS3:
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=0, GW IP address=IP23 (and BGP Encapsulation Extended
Community).
(3) DGW1 and DGW2 import both received routes based on the route-
target:
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o M2 is added to the MAC-VRF10 MAC FIB along with its
corresponding tunnel information. For the VXLAN use case, the
VTEP will be derived from the MAC/IP route BGP next-hop and
VNI from the Ethernet Tag or MPLS fields. IP23 - M2 is added
to the ARP table.
o SN1/24 is added to the designated routing context in DGW1 and
DGW2 with next-hop IP23 pointing at the local MAC-VRF10.
(4) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table and next-hop=IP23 is found. Since IP23 is an
overlay next-hop, a recursive route resolution for IP23 is
required.
o IP23 is resolved to M2 in the ARP table, and M2 is resolved to
the tunnel information given by the MAC-VRF (remote VTEP and
VNI for the VXLAN case).
o The IP packet destined to IPx is encapsulated with:
. Source inner MAC = IRB1 MAC
. Destination inner MAC = M2
. Tunnel information provided by the MAC FIB (VNI, VTEP IPs
and MACs for the VXLAN case)
(5) When the packet arrives at NVE2:
o Based on the tunnel information (VNI for the VXLAN case), the
MAC-VRF10 context is identified for a MAC lookup.
o Encapsulation is stripped-off and based on a MAC lookup
(assuming MAC forwarding on the egress NVE), the packet is
forwarded to TS2, where it will be properly routed.
(6) When the redundancy protocol running between TS2 and TS3 appoints
TS3 as the new active TS for SN1, TS3 will now own the floating
IP23 and will signal this new ownership (GARP message or
similar). Upon receiving the new owner's notification, NVE3 will
issue a route type 2 for M3-IP23. DGW1 and DGW2 will update their
ARP tables with the new MAC resolving the floating IP. No changes
are carried out in the VRF routing table.
In the DGW1/2 BGP RIB, there will be two route type 5 routes for SN1
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(from NVE2 and NVE3) but only the one with the same BGP next-hop as
the IP23 RT-2 BGP next-hop will be valid.
5.3 ESI next-hop ("Bump in the wire") use-case
The following figure illustrates and example of inter-subnet
forwarding for a subnet route that uses an ESI as an overlay next-
hop. In this use-case, TS2 and TS3 are layer-2 VA devices without any
IP address that can be included as an overlay next-hop in the GW IP
field of the IP Prefix route.
NVE2 DGW1
+-----------+ +---------+ +-------------+
+---TS2(VA)--|(MAC-VRF10)|-| |----|(MAC-VRF10) |
| ESI23 +-----------+ | | | IRB1\ |
| + | | | (IP-VRF)|---+
| | | | +-------------+ _|_
SN1 | | VXLAN/ | ( )
| | | nvGRE | DGW2 ( WAN )
| + NVE3 | | +-------------+ (___)
| ESI23 +-----------+ | |----|(MAC-VRF10) | |
+---TS3(VA)--|(MAC-VRF10)|-| | | IRB2\ | |
+-----------+ +---------+ | (IP-VRF)|---+
+-------------+
Figure 5 ESI next-hop use-case
Since neither TS2 nor TS3 can run any routing protocol and have no IP
address assigned, an ESI, i.e. ESI23, will be provisioned on the
attachment ports of NVE2 and NVE3. This model supports VA redundancy
in a similar way as the one described in section 5.2 for the floating
IP next-hop use-case, only using the EVPN Ethernet A-D route instead
of the MAC advertisement route to advertise the location of the
overlay next-hop. The procedure is explained below:
(1) NVE2 advertises the following BGP routes for TS2:
o Route type 1 (Ethernet A-D route for EVI-10) containing:
ESI=ESI23 and the corresponding tunnel information (Ethernet
Tag and/or MPLS label), as well as the BGP Encapsulation
Extended Community. Assuming the ESI is active on NVE2, NVE2
will advertise this route.
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=ESI23, GW IP address=0 (and BGP Encapsulation Extended
Community).
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(2) NVE3 advertises the following BGP routes for TS3:
o Route type 1 (Ethernet A-D route for EVI-10) containing:
ESI=ESI23 and the corresponding tunnel information (Ethernet
Tag and/or MPLS label), as well as the BGP Encapsulation
Extended Community. NVE3 will advertise this route assuming
the ESI is active on NVE2. Note that if the resiliency
mechanism for TS2 and TS3 is in active-active mode, both NVE2
and NVE3 will send the A-D route. Otherwise, that is, the
resiliency is active-standby, only the NVE owning the active
ESI will advertise the Ethernet A-D route for ESI23.
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=23, GW IP address=0 (and BGP Encapsulation Extended
Community).
(3) DGW1 and DGW2 import the received routes based on the route-
target:
o The tunnel information to get to ESI23 is installed in DGW1
and DGW2. For the VXLAN use case, the VTEP will be derived
from the Ethernet A-D route BGP next-hop and VNI from the
Ethernet Tag or MPLS fields (see [EVPN-OVERLAYS]).
o SN1/24 is added to the designated routing context in DGW1 and
DGW2 with next-hop ESI23 pointing at the local MAC-VRF10.
(4) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table and next-hop=ESI23 is found. Since ESI23 is an
overlay next-hop, a recursive route resolution is required to
find the egress NVE where ESI23 resides.
o The IP packet destined to IPx is encapsulated with:
. Source inner MAC = IRB1 MAC
. Destination inner MAC = M2 (this MAC will be obtained
after a lookup in the IP-VRF ARP table or in the MAC-
VRF10 FDB table associated to ESI23).
. Tunnel information provided by the Ethernet A-D route for
ESI23 (VNI, VTEP IP and MACs for the VXLAN case).
(5) When the packet arrives at NVE2:
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o Based on the tunnel information (VNI for the VXLAN case), the
MAC-VRF10 context is identified for a MAC lookup (assuming MAC
disposition model).
o Encapsulation is stripped-off and based on a MAC lookup
(assuming MAC forwarding on the egress NVE), the packet is
forwarded to TS2, where it will be properly forwarded.
(6) If the redundancy protocol running between TS2 and TS3 follows an
active/standby model and there is a failure, appointing TS3 as
the new active TS for SN1, TS3 will now own the connectivity to
SN1 and will signal this new ownership. Upon receiving the new
owner's notification, NVE3 will issue a route type 1 for ESI23,
whereas NVE2 will withdraw its Ethernet A-D route for ESI23. DGW1
and DGW2 will update their tunnel information to resolve ESI23.
No changes are carried out in the IP-VRF routing table.
In the DGW1/2 BGP RIB, there will be two route type 5 routes for SN1
(from NVE2 and NVE3) but only the one with the same BGP next-hop as
the ESI23 route type 1 BGP next-hop will be valid.
5.4 IRB forwarding on NVEs for Subnets (IP-VRF-to-IP-VRF)
This use-case is similar to the scenario described in "IRB forwarding
on NVEs for Tenant Systems" in [EVPN-INTERSUBNET], however the new
requirement here is the advertisement of IP Prefixes as opposed to
only host routes. In the previous examples, the MAC-VRF instance can
connect IRB interfaces and any other Tenant Systems connected to it.
EVPN provides connectivity for:
a) Traffic destined to the IRB IP interfaces as well as
b) Traffic destined to IP subnets seating behind the TS, e.g. SN1 or
SN2.
In order to provide connectivity for (a) we need MAC/IP routes (RT-2)
distributing IRB MACs and IPs. Connectivity type (b) is accomplished
by the exchange of IP Prefix routes (RT-5) for IPs and subnets
seating behind certain overlay next-hops.
In some cases, subnets may be advertised in IP Prefix routes without
any overlay next-hop since the RT-5 itself provides all the
forwarding information required to send the packets to the egress NVE
and no recursive route resolution is needed. This use case is
depicted in the diagram below and we refer to it as the "IRB
forwarding on NVEs for Subnets" or "IP-VRF-to-IP-VRF" use-case:
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NVE1
+------------+
IP1-----|(MAC-VRF1) | DGW1
| \ | +---------+ +--------+
| (IP-VRF)|----| |-|(IP-VRF)|----+
| / | | | +--------+ |
|---|(MAC-VRF2) | | | _|_
| +------------+ | | ( )
SN1| | VXLAN/ | ( WAN )
| NVE2 | nvGRE | (___)
| +------------+ | | |
|---|(MAC-VRF2) | | | DGW2 |
| \ | | | +--------+ |
| (IP-VRF)|----| |-|(IP-VRF)|----+
| / | +---------+ +--------+
SN2-----|(MAC-VRF3) |
+------------+
Figure 6 Inter-subnet forwarding on NVEs for Subnets
In this case, we need to provide connectivity from/to IP hosts in
SN1, SN2, IP1 and hosts seating at the other end of the WAN. There is
no need to define IRB interfaces to interconnect the IP-VRF instances
among the NVEs for the same tenant. This is the reason why we refer
to this solution as "IP-VRF-to-IP-VRF" solution.
In this case, the EVPN route type 5 will be used to advertise the IP
Prefixes, along with the Router's MAC Extended Community as defined
in [EVPN-INTERSUBNET]. Each NVE/DGW will advertise an RT-5 for each
of its subnet prefixes with the following fields:
o RD as per [EVPN].
o Eth-Tag ID = 0 assuming VLAN-based service.
o IP address length and IP address, as explained in the previous
sections.
o GW IP address=0 and ESI=0, that is, no overlay next-hop is
required in this use-case, since the BGP next-hop is enough to
find the egress NVE to forward the packets to.
o MPLS label or VNID corresponding to the IP-VRF.
Each RT-5 will be sent with a route-target identifying the tenant
(IP-VRF) and two BGP extended communities:
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o The first one is the BGP Encapsulation Extended Community, as
per [RFC5512], identifying the tunnel type.
o The second one is the Router's MAC Extended Community as per
[EVPN-INTERSUBNET] containing the MAC address associated to
the NVE advertising the route. This MAC address identifies the
NVE/DGW and MAY be re-used for all the IP-VRFs in the node.
The ingress NVE will use this MAC address as the inner MAC
destination address in the packets forwarded to the owner of
the RT-5.
Example of prefix advertisement for the ipv4 prefix SN1/24 advertised
from NVE1:
(1) NVE1 advertises the following BGP route for SN1:
o Route type 5 (IP Prefix route) containing: Eth-Tag=0, IPL=24,
IP=SN1, MPLS Label=10. An [RFC5512] BGP Encapsulation Extended
Community will be sent, where Tunnel-type= VXLAN or NVGRE. A
Router's MAC Extended Community will also be sent along with
the RT-5, where the Router's MAC address value will contain
the NVE1 MAC.
(2) DGW1 imports the received route from NVE1 and SN1/24 is added to
the designated IP-VRF. The next-hop for SN1/24 will be given by
the route type 5 BGP next-hop (NVE1), which is resolved to a
tunnel. For instance: if the tunnel is VXLAN based, the BGP next-
hop will be resolved to a VXLAN tunnel where: destination-VTEP=
NVE1 IP, VNI=10, inner destination MAC = NVE1 MAC (derived from
the Router's MAC Extended Community value).
(3) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table and next-hop= "NVE1 IP" is found. The tunnel
information to encapsulate the packet will be derived from the
route type 5 received for SN1.
o The IP packet destined to IPx is encapsulated with: Source
inner MAC = DGW1 MAC, Destination inner MAC = NVE1 MAC, Source
outer IP (source VTEP) = DGW1 IP, Destination outer IP
(destination VTEP) = NVE1 IP.
(4) When the packet arrives at NVE1:
o Based on the tunnel information (VNI for the VXLAN case), the
routing context is identified for an IP lookup.
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o An IP lookup is performed in the routing context, where SN1
turns out to be a local subnet associated to MAC-VRF2. A
subsequent lookup in the ARP table and the MAC-VRF FIB will
return the forwarding information for the packet in EVI-2.
6. Conclusions
A new EVPN route type 5 for the advertisement of IP Prefixes is
described in this document. This new route type has a differentiated
role from the RT-2 route and addresses all the Data Center (or NVO-
based networks in general) inter-subnet connectivity scenarios in
which an IP Prefix advertisement is required. Using this new RT-5, an
IP Prefix may be advertised along with an overlay next-hop that can
be a GW IP address or an ESI, or without an overlay next-hop, in
which case the BGP next-hop will point at the egress NVE and the MAC
in the Router's MAC Extended Community will provide the inner MAC
destination address to be used. As discussed throughout the document,
the existing EVPN RT-2 does not meet the requirements for all the DC
use cases, therefore a new EVPN route type is required.
This new EVPN route type 5 decouples the IP Prefix advertisements
from the MAC route advertisements in EVPN, hence:
a) Allows the clean and clear advertisements of ipv4 or ipv6 prefixes
in an NLRI with no MAC addresses in the route key, so that only IP
information is used in BGP route comparisons.
b) Since the route type is different from the MAC/IP advertisement
route, the advertisement of prefixes will be excluded from all the
procedures defined for the advertisement of VM MACs, e.g. MAC
Mobility or aliasing. As a result of that, the current EVPN
procedures do not need to be modified.
c) Allows a flexible implementation where the prefix can be linked to
different types of next-hops: overlay IP address, overlay ESI,
underlay IP next-hops, etc.
d) An EVPN implementation not requiring IP Prefixes can simply
discard them by looking at the route type value. An unknown route
type MUST be ignored by the receiving NVE/PE.
7. 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 RFC-2119
[RFC2119].
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8. Security Considerations
9. IANA Considerations
10. References
10.1 Normative References
[RFC4364]Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006, <http://www.rfc-
editor.org/info/rfc4364>.
10.2 Informative References
[EVPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-11.txt, work in progress, October, 2014
[EVPN-OVERLAYS] Sajassi-Drake et al., "A Network Virtualization
Overlay Solution using EVPN", draft-ietf-bess-evpn-overlay-00.txt,
work in progress, November, 2014
[EVPN-INTERSUBNET] Sajassi et al., "IP Inter-Subnet Forwarding in
EVPN", draft-ietf-bess-evpn-inter-subnet-forwarding-00.txt, work
in progress, November, 2014
11. Acknowledgments
The authors would like to thank Mukul Katiyar and Senthil
Sathappan for their valuable feedback and contributions. The
following people also helped improving this document with their
feedback: Antoni Przygienda and Thomas Morin.
12. Authors' Addresses
Jorge Rabadan
Alcatel-Lucent
777 E. Middlefield Road
Mountain View, CA 94043 USA
Email: jorge.rabadan@alcatel-lucent.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Florin Balus
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Nuage Networks
Email: florin@nuagenetworks.net
Aldrin Isaac
Bloomberg
Email: aisaac71@bloomberg.net
Senad Palislamovic
Alcatel-Lucent
Email: senad.palislamovic@alcatel-lucent.com
John E. Drake
Juniper Networks
Email: jdrake@juniper.net
Ali Sajassi
Cisco
Email: sajassi@cisco.com
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