Internet DRAFT - draft-snr-bess-evpn-proxy-arp-nd
draft-snr-bess-evpn-proxy-arp-nd
BESS Workgroup J. Rabadan, Ed.
Internet Draft S. Sathappan
K. Nagaraj
Intended status: Informational W. Henderickx
G. Hankins
Alcatel-Lucent
T. King
D. Melzer
DE-CIX
E. Nordmark
Arista Networks
Expires: April 8, 2016 October 6, 2015
Operational Aspects of Proxy-ARP/ND in EVPN Networks
draft-snr-bess-evpn-proxy-arp-nd-02
Abstract
The MAC/IP Advertisement route specified in [RFC7432] can optionally
carry IPv4 and IPv6 addresses associated with a MAC address. Remote
PEs can use this information to reply locally (act as proxy) to IPv4
ARP requests and IPv6 Neighbor Solicitation messages (or 'unicast-
forward' them to the owner of the MAC) and reduce/suppress the
flooding produced by the Address Resolution procedure. This EVPN
capability is extremely useful in Internet Exchange Points (IXPs) and
Data Centers (DCs) with large broadcast domains, where the amount of
ARP/ND flooded traffic causes issues on routers and CEs, as explained
in [RFC6820]. This document describes how the [RFC7432] EVPN proxy-
ARP/ND function may be implemented to help IXPs and other operators
deal with the issues derived from Address Resolution in large
broadcast domains.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. The DC Use-Case . . . . . . . . . . . . . . . . . . . . . . 4
2.2. The IXP Use-Case . . . . . . . . . . . . . . . . . . . . . 4
3. Solution Requirements . . . . . . . . . . . . . . . . . . . . . 5
4. Solution Description . . . . . . . . . . . . . . . . . . . . . 6
4.1. Learning Sub-Function . . . . . . . . . . . . . . . . . . . 8
4.1.1. Proxy-ND and the NA Flags . . . . . . . . . . . . . . . 10
4.2. Reply Sub-Function . . . . . . . . . . . . . . . . . . . . 11
4.3. Unicast-forward Sub-Function . . . . . . . . . . . . . . . 12
4.4. Maintenance Sub-Function . . . . . . . . . . . . . . . . . 12
4.5. Flooding (to Remote PEs) Reduction/Suppression . . . . . . 13
4.6. Duplicate IP Detection . . . . . . . . . . . . . . . . . . 14
5. Solution Benefits . . . . . . . . . . . . . . . . . . . . . . . 16
6. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 16
6.1. All Dynamic Learning . . . . . . . . . . . . . . . . . . . 17
6.2. Dynamic Learning with Proxy-ARP/ND . . . . . . . . . . . . 17
6.3. Hybrid Dynamic Learning and Static Provisioning with
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Proxy-ARP/ND . . . . . . . . . . . . . . . . . . . . . . . 17
6.4 All Static Provisioning with Proxy-ARP/ND . . . . . . . . . 17
6.5 Deployment Scenarios in IXPs . . . . . . . . . . . . . . . . 18
6.6 Deployment Scenarios in DCs . . . . . . . . . . . . . . . . 19
7. Conventions Used in this Document . . . . . . . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . . 21
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
1. Terminology
BUM: Broadcast, Unknown unicast and Multicast layer-2 traffic.
ARP: Address Resolution Protocol.
GARP: Gratuitous ARP message.
ND: Neighbor Discovery Protocol.
NS: Neighbor Solicitation message.
NA: Neighbor Advertisement.
IXP: Internet eXchange Point.
IXP-LAN: it refers to the IXP's large Broadcast Domain to where
Internet routers are connected.
DC: Data Center.
IP->MAC: it refers to an IP address associated to a MAC address. The
entries may be of three different types: dynamic, static or EVPN-
learned.
SN-multicast address: Refers to the Solicited-Node IPv6 multicast
address used by NS messages.
NUD: Neighbor Unreachability Detection, as per [RFC4861].
DAD: Duplicate Address Detection, as per [RFC4861].
SLLA: Source Link Layer Address, as per [RFC4861].
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TLLA: Target Link Layer Address, as per [RFC4861].
R-bit: Router Flag in NA messages, as per [RFC4861].
O-bit: Override Flag in NA messages, as per [RFC4861].
S-bit: Solicited Flag in NA messages, as per [RFC4861].
RT2: EVPN Route type 2 or MAC/IP Advertisement route, as per
[RFC7432].
MAC or IP DA: MAC or IP Destination Address.
MAC or IP SA: MAC or IP Source Address.
AS-MAC: Anti-spoofing MAC.
2. Introduction
As specified in [RFC7432] the IP Address field in the MAC/IP
Advertisement route may optionally carry one of the IP addresses
associated with the MAC address. A PE may learn local IP->MAC pairs
and advertise them in EVPN MAC/IP routes. The remote PEs may add
those IP->MAC pairs to their Proxy-ARP/ND tables and reply to local
ARP requests or Neighbor Solicitations (or 'unicast-forward' those
packets to the owner MAC), reducing and even suppressing in some
cases the flooding in the EVPN network.
EVPN and its associated Proxy-ARP/ND function are extremely useful in
Data Centers (DCs) or Internet Exchange Points (IXPs) with large
broadcast domains, where the amount of ARP/ND flooded traffic causes
issues on routers and CEs. [RFC6820] describes the Address Resolution
problems in Large Data Center networks.
This document describes how the [RFC7432] proxy-ARP/ND function may
be implemented to help IXPs, DCs and other operators deal with the
issues derived from Address Resolution in large broadcast domains.
2.1. The DC Use-Case
As described in [RFC6820] the IPv4 and IPv6 Address Resolution can
create a lot of issues in large DCs. The amount of flooding that
Address Resolution creates, as well as other associated issues can be
mitigated with the use of EVPN and its proxy-ARP/ND function.
2.2. The IXP Use-Case
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The implementation described in this document is especially useful in
IXP networks.
A typical IXP provides access to a large layer-2 peering network,
where (hundreds of) Internet routers are connected. Because of the
requirement to connect all routers to a single layer-2 network the
peering networks use IPv4 layer-3 addresses in length ranges from /21
to /24, which can create very large broadcast domains. This peering
network is transparent to the Customer Edge (CE) devices and
therefore floods any ARP request or NS messages to all the CEs in the
network. Unsolicited GARP and NA messages are flooded to all the CEs
too.
In these IXP networks, most of the CEs are typically peering routers
and roughly all the BUM traffic is originated by the ARP and ND
address resolution procedures. This ARP/ND BUM traffic causes
significant data volumes that reach every single router in the
peering network. Since the ARP/ND messages are processed in software
processors and they take high priority in the routers, heavy loads of
ARP/ND traffic can cause some routers to run out of resources. CEs
disappearing from the network may cause Address Resolution explosions
that can make a router with limited processing power fail to keep BGP
sessions running.
The issue may be better in IPv6 routers, since ND uses SN-multicast
address in NS messages, however ARP uses broadcast and has to be
processed by all the routers in the network. Some routers may also be
configured to broadcast periodic GARPs [RFC5227]. The amount of
ARP/ND flooded traffic grows exponentially with the number of IXP
participants, therefore the issue can only go worse as new CEs are
added.
In order to deal with this issue, IXPs have developed certain
solutions over the past years. One example is the ARP-Sponge daemon
[ARP-Sponge]. While these solutions may mitigate the issues of
Address Resolution in large broadcasts domains, EVPN provides new
more efficient possibilities to IXPs. EVPN and its proxy-ARP/ND
function may help solve the issue in a distributed and scalable way,
fully integrated with the PE network.
3. Solution Requirements
The distributed EVPN proxy-ARP/ND function described in this document
SHOULD meet the following requirements:
o The solution SHOULD support the learning of the CE IP->MAC entries
on the EVPN PEs via the management, control or data planes. An
implementation SHOULD allow to intentionally enable or disable
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those possible learning mechanisms.
o The solution MAY suppress completely the flooding of the ARP/ND
messages in the EVPN network, assuming that all the CE IP->MAC
addresses local to the PEs are known or provisioned on the PEs from
a management system. Note that in this case, the unknown unicast
traffic can also be suppressed, since all the expected unicast
traffic will be destined to known MAC addresses in the PE MAC-VRFs.
o The solution MAY reduce significantly the flooding of the ARP/ND
messages in the EVPN network, assuming that some or all the CE
IP->MAC addresses are learned on the data plane by snooping ARP/ND
messages issued by the CEs.
o The solution MAY provide a way to refresh periodically the CE
IP->MAC entries learned through the data plane, so that the IP->MAC
entries are not withdrawn by EVPN when they age out unless the CE
is not active anymore. This option helps reducing the EVPN control
plane overhead in a network with active CEs that do not send
packets frequently.
o The solution SHOULD provide a mechanism to detect duplicate IP
addresses. In case of duplication, the detecting PE should not
reply to requests for the duplicate IP. Instead, the PE should
alert the operator and may optionally prevent any other CE from
sending traffic to the duplicate IP.
o The solution MUST NOT change any existing behavior in the CEs
connected to the EVPN PEs.
4. Solution Description
Figure 1 illustrates an example EVPN network where the Proxy-ARP/ND
function is enabled.
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MAC-VRF1
Proxy-ARP/ND
+------------+
IP1/M1 +----------------------------+ |IP1->M1 EVPN|
GARP --->Proxy-ARP/ND | |IP2->M2 EVPN|
+---+ +----+---+ RT2(IP1/M1) | |IP3->M3 sta |
|CE1+------+MAC-VRF1| ------> +------+---|IP4->M4 dyn |
+---+ +--------+ | +------------+
PE1 | +--------+ Who has IP1?
| EVPN | |MAC-VRF1| <----- +---+
| EVI1 | | | | |CE3|
IP2/M2 | | | | -----> +---+
GARP --->Proxy-ARP/ND | +--------+ | IP1->M1
+---+ +--------+ RT2(IP2/M2) | |
|CE2+----+MAC-VRF1| ------> +--------------+
+---+ +--------+ PE3| +---+
PE2 | +----+CE4|
+----------------------------+ +---+
<---IP4/M4 GARP
Figure 1 Proxy-ARP/ND network example
When the Proxy-ARP/ND function is enabled in the MAC-VRFs of the EVPN
PEs, each PE creates a Proxy table specific to that MAC-VRF that can
contain three types of Proxy-ARP/ND entries:
a) Dynamic entries: learned by snooping CE's ARP and ND messages. For
instance, IP4->M4 in Figure 1.
b) Static entries: provisioned on the PE by the management system.
For instance, IP3->M3 in Figure 1.
c) EVPN-learned entries: learned from the IP/MAC information encoded
in the received RT2's coming from remote PEs. For instance, IP1-
>M1 and IP2->M2 in Figure 1.
As a high level example, the operation of the EVPN Proxy-ARP/ND
function in the network of Figure 1 is described below. In this
example we assume IP1, IP2 and IP3 are IPv4 addresses:
1. Proxy-ARP/ND is enabled in MAC-VRF1 of PE1, PE2 and PE3.
2. The PEs start adding dynamic, static and EVPN-learned entries to
their Proxy tables:
a. PE3 adds IP1->M1 and IP2->M2 based on the EVPN routes received
from PE1 and PE2. Those entries were previously learned as
dynamic entries in PE1 and PE2 respectively, and advertised in
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BGP EVPN.
b. PE3 adds IP4->M4 as dynamic. This entry is learned by snooping
the corresponding ARP messages sent by CE4.
c. An operator also provisions the static entry IP3->M3.
3. When CE3 sends an ARP Request asking for IP1, PE3 will:
a. Intercept the ARP Request and perform a Proxy-ARP lookup for
IP1.
b. If the lookup is successful (as in Figure 1), PE3 will send an
ARP Reply with IP1->M1. The ARP Request will not be flooded to
the EVPN network or any other local CEs.
c. If the lookup is not successful, PE3 will flood the ARP Request
in the EVPN network and the other local CEs.
As PE3 learns more and more host entries in the Proxy-ARP/ND table,
the flooding of ARP Request messages is reduced and in some cases it
can even be suppressed. In a network where most of the participant
CEs are not moving between PEs and they advertise their presence with
GARPs or unsolicited NA messages, the ARP/ND flooding as well as the
unknown unicast flooding can practically be suppressed. In an EVPN-
based IXP network, where all the entries are Static, the ARP/ND
flooding is in fact totally suppressed.
The Proxy-ARP/ND function can be structured in six sub-functions or
procedures:
1. Learning sub-function
2. Reply sub-function
3. Unicast-forward sub-function
4. Maintenance sub-function
5. Flooding reduction/suppression sub-function
6. Duplicate IP detection sub-function
A Proxy-ARP/ND implementation MAY support all those sub-functions or
only a subset of them. The following sections describe each
individual sub-function.
4.1. Learning Sub-Function
A Proxy-ARP/ND implementation SHOULD support static, dynamic and
EVPN-learned entries.
Static entries are provisioned from the management plane. The
provisioned static IP->MAC entry SHOULD be advertised in EVPN with a
MAC Mobility extended community where the static flag is set to 1, as
per [RFC7432]. A static entry MAY associate and IP to a list of
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potential MACs, i.e. IP1->(MAC1,MAC2..MACN). When there is more than
one MAC in the list of allowed MACs, the PE will not advertise any
IP->MAC in EVPN until a local ARP/NA message or any other frame is
received from the CE. Upon receiving traffic from the CE, the PE will
check that the source MAC is included in the list of allowed MACs.
Only in that case, the PE will activate the IP->MAC and advertise it
in EVPN.
EVPN-learned entries MUST be learned from received valid EVPN MAC/IP
Advertisement routes containing a MAC and IP address.
Dynamic entries are learned in different ways depending on whether
the entry contains an IPv4 or IPv6 address:
a) Proxy-ARP dynamic entries:
They SHOULD be learned by snooping any ARP packet (Ethertype
0x0806) received from the CEs attached to the MAC-VRF. The
Learning function will add the Sender MAC and Sender IP of the
snooped ARP packet to the Proxy-ARP table. Note that MAC and IPs
with value 0 SHOULD NOT be learned.
b) Proxy-ND dynamic entries:
They SHOULD be learned out of the Target Address and TLLA
information in NA messages (Ethertype 0x86DD, ICMPv6 type 136)
received from the CEs attached to the MAC-VRF. A Proxy-ND
implementation SHOULD NOT learn IP->MAC entries from NS messages,
since they don't contain the R-bit Flag required by the Proxy-ND
reply function. See section 4.1.1 for more information about the
R-bit flag.
Note that if the O-bit is zero in the received NA message, the
IP->MAC SHOULD only be learned in case IPv6 'anycast' is enabled
in the EVI.
The following procedure associated to the Learning sub-function is
recommended:
o When a new Proxy-ARP/ND EVPN or static active entry is learned (or
provisioned), the PE SHOULD send an unsolicited GARP or NA message
to the access CEs. The PE SHOULD send an unsolicited GARP/NA
message for dynamic entries only if the ARP/NA message creating the
entry was NOT flooded before. This unsolicited GARP/NA message
makes sure the CE ARP/ND caches are updated even if the ARP/NS/NA
messages from remote CEs are not flooded in the EVPN network.
Note that if a Static entry is provisioned with the same IP as an
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existing EVPN-learned or Dynamic entry, the Static entry takes
precedence.
4.1.1. Proxy-ND and the NA Flags
[RFC4861] describes the use of the R-bit flag in IPv6 Address
Resolution:
o Nodes capable of routing IPv6 packets must reply to NS messages
with NA messages where the R-bit flag is set (R-bit=1).
o Hosts that are not able to route IPv6 packets must indicate that
inability by replying with NA messages that contain R-bit=0.
The use of the R-bit flag in NA messages has an impact on how hosts
select their default gateways when sending packets off-link:
o Hosts build a Default Router List based on the received RAs and NAs
with R-bit=1. Each cache entry has an IsRouter flag, which must be
set based on the R-bit flag in the received NAs. A host can choose
one or more Default Routers when sending packets off-link.
o In those cases where the IsRouter flag changes from TRUE to FALSE
as a result of a NA update, the node MUST remove that router from
the Default Router List and update the Destination Cache entries
for all destinations using that neighbor as a router, as specified
in [RFC4861] section 7.3.3. This is needed to detect when a node
that is used as a router stops forwarding packets due to being
configured as a host.
The R-bit and O-bit will be learned in the following ways:
o Static entries SHOULD have the R-bit information added by the
management interface. The O-bit information MAY also be added by
the management interface.
o Dynamic entries SHOULD learn the R-bit and MAY learn the O-bit from
the snooped NA messages used to learn the IP->MAC itself.
o EVPN-learned entries SHOULD learn the R-bit and MAY learn the O-bit
from the ND Extended Community received from EVPN along with the
RT2 used to learn the IP->MAC itself. Please refer to [EVPN-NA-
FLAGS]. If no ND extended community is received, the PE will add
the default R-bit/O-bit to the entry. The default R-bit SHOULD be
an administrative choice. The default O-bit SHOULD be 1.
Note that the O-bit SHOULD only be learned if 'anycast' is enabled in
the EVI. If so, Duplicate IP Detection must be disabled so that the
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PE is able to learn the same IP mapped to different MACs in the same
Proxy-ND table. If 'anycast' is disabled, NA messages with O-bit = 0
will not create a proxy-ND entry, hence no EVPN advertisement with ND
extended community will be generated.
4.2. Reply Sub-Function
This sub-function will reply to Address Resolution
requests/solicitations upon successful lookup in the Proxy-ARP/ND
table for a given IP address. The following considerations should be
taken into account:
a) When replying to ARP Request or NS messages, the PE SHOULD use the
Proxy-ARP/ND entry MAC address as MAC SA. This is recommended so
that the resolved MAC can be learned in the MAC FIB of potential
Layer-2 switches seating between the PE and the CE requesting the
Address Resolution.
b) A PE SHOULD NOT reply to a request/solicitation received on the
same attachment circuit over which the IP->MAC is learned. In this
case the requester and the requested IP are assumed to be
connected to the same layer-2 switch/access network linked to the
PE's attachment circuit, and therefore the requested IP owner will
receive the request directly.
c) A PE SHOULD reply to broadcast/multicast Address Resolution
messages, that is, ARP-Request, NS messages as well as DAD NS
messages. A PE SHOULD NOT reply to unicast Address Resolution
requests (for instance, NUD NS messages).
d) A PE SHOULD include the R-bit learned for the IP->MAC entry in the
NA messages (see section 4.1.1). The S-bit will be set/unset as
per [RFC4861]. The O-bit will be included if IPv6 'anycast' is
enabled in the EVI and it is learned for the IP->MAC entry. If
'anycast' is enabled and there are more than one MAC for a given
IP, the PE will reply to NS messages with as many NA responses as
'anycast' entries are in the proxy-ND table.
e) A PE SHOULD NOT reply to ARP probes received from the CEs. An ARP
probe is an ARP request constructed with an all-zero sender IP
address that may be used by hosts for IPv4 Address Conflict
Detection [RFC5227].
f) A PE SHOULD only reply to ARP-Request and NS messages with the
format specified in [RFC0826] and [RFC4861] respectively. Received
ARP-Requests and NS messages with unknown options SHOULD be either
forwarded (as unicast packets) to the owner of the requested IP
(assuming the MAC is known in the proxy-ARP/ND table and MAC-VRF)
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or discarded. An administrative option to control this behavior
('unicast-forward' or 'discard') SHOULD be supported. The
'unicast-forward' option is described in section 4.3.
4.3. Unicast-forward Sub-Function
As discussed in section 4.2. in some cases the operator may want to
'unicast-forward' certain ARP-Request and NS messages as opposed to
reply to them. The operator SHOULD be able to activate this option
with one of the following parameters:
a) unicast-forward always
b) unicast-forward unknown-options
If 'unicast-forward always' is enabled, the PE will perform a proxy-
ARP/ND table lookup and in case of a hit, the PE will forward the
packet to the owner of the MAC found in the proxy-ARP/ND table. This
is irrespective of the options carried in the ARP/ND packet. This
option provides total transparency in the EVI and yet reduces the
amount of flooding significantly.
If 'unicast-forward unknown-options' is enabled, upon a successful
proxy-ARP/ND lookup, the PE will perform a 'unicast-forward' action
only if the ARP-Request or NS messages carry unknown options, as
explained in section 4.2. As an example, this would allow to enable
proxy-ND and Secure ND [RFC3971] in the same EVI. The 'unicast-
forward unknown-options' configuration allows the support of new
applications using ARP/ND in the EVI while still reducing the
flooding at the same time.
4.4. Maintenance Sub-Function
The Proxy-ARP/ND tables SHOULD follow a number of maintenance
procedures so that the dynamic IP->MAC entries are kept if the owner
is active and flushed if the owner is no longer in the network. The
following procedures are recommended:
a) Age-time
A dynamic Proxy-ARP/ND entry SHOULD be flushed out of the table if
the IP->MAC has not been refreshed within a given age-time. The
entry is refreshed if an ARP or NA message is received for the
same IP->MAC entry. The age-time is an administrative option and
its value should be carefully chosen depending on the specific
use-case: in IXP networks (where the CE routers are fairly static)
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the age-time may normally be longer than in DC networks (where
mobility is required).
b) Send-refresh option
The PE MAY send periodic refresh messages (ARP/ND "probes") to the
owners of the dynamic Proxy-ARP/ND entries, so that the entries
can be refreshed before they age out. The owner of the IP->MAC
entry would reply to the ARP/ND probe and the corresponding entry
age-time reset. The periodic send-refresh timer is an
administrative option and is recommended to be a third of the age-
time or a half of the age-time in scaled networks.
An ARP refresh issued by the PE will be an ARP-Request message
with the Sender's IP = 0 sent from the PE's MAC SA. If the PE has
an IP address in the subnet, for instance on an IRB interface,
then it MAY use it as a source for the ARP request (instead of
Sender's IP = 0). An ND refresh will be a NS message issued from
the PE's MAC SA and a Link Local Address associated to the PE's
MAC.
The refresh request messages should be sent only for dynamic
entries and not for static or EVPN-learned entries. Even though
the refresh request messages are broadcast or multicast, the PE
SHOULD only send the message to the attachment circuit associated
to the MAC in the IP->MAC entry.
The age-time and send-refresh options are used in EVPN networks to
avoid unnecessary EVPN RT2 withdrawals: if refresh messages are sent
before the corresponding MAC-VRF FIB and Proxy-ARP/ND age-time for a
given entry expires, inactive but existing hosts will reply,
refreshing the entry and therefore avoiding unnecessary MAC and MAC-
IP withdrawals in EVPN. Both entries (MAC in the MAC-VRF and IP->MAC
in Proxy-ARP/ND) are reset when the owner replies to the ARP/ND
probe. If there is no response to the ARP/ND probe, the MAC and
IP->MAC entries will be legitimately flushed and the RT2s withdrawn.
4.5. Flooding (to Remote PEs) Reduction/Suppression
The Proxy-ARP/ND function implicitly helps reducing the flooding of
ARP Request and NS messages to remote PEs in an EVPN network.
However, in certain use-cases, the flooding of ARP/NS/NA messages
(and even the unknown unicast flooding) to remote PEs can be
suppressed completely in an EVPN network.
For instance, in an IXP network, since all the participant CEs are
well known and will not move to a different PE, the IP->MAC entries
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may be all provisioned by a management system. Assuming the entries
for the CEs are all provisioned on the local PE, a given Proxy-ARP/ND
table will only contain static and EVPN-learned entries. In this
case, the operator may choose to suppress the flooding of ARP/NS/NA
to remote PEs completely.
The flooding may also be suppressed completely in IXP networks with
dynamic Proxy-ARP/ND entries assuming that all the CEs are directly
connected to the PEs and they all advertise their presence with a
GARP/unsolicited-NA when they connect to the network.
In networks where fast mobility is expected (DC use-case), it is not
recommended to suppress the flooding of unknown ARP-Requests/NS or
GARPs/unsolicited-NAs. Unknown ARP-Requests/NS refer to those
ARP-Request/NS messages for which the Proxy-ARP/ND lookups for the
requested IPs do not succeed.
In order to give the operator the choice to suppress/allow the
flooding to remote PEs, a PE MAY support administrative options to
individually suppress/allow the flooding of:
o Unknown ARP-Request and NS messages.
o GARP and unsolicited-NA messages.
The operator will use these options based on the expected behavior in
the CEs.
4.6. Duplicate IP Detection
The Proxy-ARP/ND function SHOULD support duplicate IP detection so
that ARP/ND-spoofing attacks or duplicate IPs due to human errors can
be detected.
ARP/ND spoofing is a technique whereby an attacker sends "fake"
ARP/ND messages onto a broadcast domain. Generally the aim is to
associate the attacker's MAC address with the IP address of another
host causing any traffic meant for that IP address to be sent to the
attacker instead.
The distributed nature of EVPN and proxy-ARP/ND allows the easy
detection of duplicated IPs in the network, in a similar way to the
MAC duplication function supported by [RFC7432] for MAC addresses.
Duplicate IP detection monitors "IP-moves" in the Proxy-ARP/ND table
in the following way:
o When an existing active IP1->MAC1 entry is modified, a PE starts an
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M-second timer (default value of M=180), and if it detects N IP
moves before the timer expires (default value of N=5), it concludes
that a duplicate IP situation has occurred. An IP move is
considered when, for instance, IP1->MAC1 is replaced by IP1->MAC2
in the Proxy-ARP/ND table.
o In order to detect the duplicate IP faster, the PE MAY send a
CONFIRM message to the former owner of the IP. A CONFIRM message is
a unicast ARP-Request/NS message sent by the PE to the MAC
addresses that previously owned the IP, when the MAC changes in the
Proxy-ARP/ND table. The CONFIRM message uses a sender's IP 0.0.0.0
in case of ARP (if the PE has an IP address in the subnet then it
MAY use it) and an IPv6 Link Local Address in case of NS. If the PE
does not receive an answer within a given timer, the new entry will
be confirmed and activated. In case of spoofing, for instance, if
IP1->MAC1 moves to IP1->MAC2, the PE may send a unicast ARP-
Request/NS message for IP1 with MAC DA= MAC1 and MAC SA= PE's MAC.
This will force the legitimate owner respond if the move to MAC2
was spoofed, and make the PE issue another CONFIRM message, this
time to MAC DA= MAC2. If both, legitimate owner and spoofer keep
replying to the CONFIRM message, the PE will detect the duplicate
IP within the M timer:
- If the IP1->MAC1 pair was previously owned by the spoofer and the
new IP1->MAC2 was from a valid CE, then the issued CONFIRM
message would trigger a response from the spoofer.
- If it were the other way around, that is, IP1->MAC1 was
previously owned by a valid CE, the CONFIRM message would trigger
a response from the CE.
Either way, if this process continues, then duplicate detection
will kick in.
o Upon detecting a duplicate IP situation:
a) The entry in duplicate detected state cannot be updated with new
dynamic or EVPN-learned entries for the same IP. The operator
MAY override the entry though with a static IP->MAC.
b) The PE SHOULD alert the operator and stop responding ARP/NS for
the duplicate IP until a corrective action is taken.
c) Optionally the PE MAY associate an "anti-spoofing-mac" (AS-MAC)
to the duplicate IP. The PE will send a GARP/unsolicited-NA
message with IP1->AS-MAC to the local CEs as well as an RT2
(with IP1->AS-MAC) to the remote PEs. This will force all the
CEs in the EVI to use the AS-MAC as MAC DA for IP1, and prevent
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the spoofer from attracting any traffic for IP1. Since the AS-
MAC is a managed MAC address known by all the PEs in the EVI,
all the PEs MAY apply filters to drop and/or log any frame with
MAC DA= AS-MAC. The advertisement of the AS-MAC as a "black-hole
MAC" that can be used directly in the MAC-VRF to drop frames is
for further study.
o The duplicate IP situation will be cleared when a corrective action
is taken by the operator, or alternatively after a HOLD-DOWN timer
(default value of 540 seconds).
The values of M, N and HOLD-DOWN timer SHOULD be a configurable
administrative option to allow for the required flexibility in
different scenarios.
For Proxy-ND, Duplicate IP Detection SHOULD only monitor IP moves for
IP->MACs learned from NA messages with O-bit=1. NA messages with
O-bit=0 would not override the ND cache entries for an existing IP.
Duplicate IP Detection for IPv6 SHOULD be disabled when IPv6
'anycast' is activated in a given EVI.
5. Solution Benefits
The solution described in this document provides the following
benefits:
a) The solution may suppress completely the flooding of the ARP/ND
and unknown-unicast messages in the EVPN network, in cases where
all the CE IP->MAC addresses local to the PEs are known and
provisioned on the PEs from a management system.
b) The solution reduces significantly the flooding of the ARP/ND
messages in the EVPN network, in cases where some or all the CE
IP->MAC addresses are learned on the data plane by snooping ARP/ND
messages issued by the CEs.
c) The solution reduces the control plane overhead and unnecessary
BGP MAC/IP Advertisements and Withdrawals in a network with active
CEs that do not send packets frequently.
d) The solution provides a mechanism to detect duplicate IP addresses
and avoid ARP/ND-spoof attacks or the effects of duplicate
addresses due to human errors.
6. Deployment Scenarios
Four deployment scenarios with different levels of ARP/ND control are
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available to operators using this solution, depending on their
requirements to manage ARP/ND: all dynamic learning, all dynamic
learning with proxy-ARP/ND, hybrid dynamic learning and static
provisioning with proxy-ARP/ND, and all static provisioning with
proxy-ARP/ND.
6.1. All Dynamic Learning
In this scenario for minimum security and mitigation, EVPN is
deployed in the peering network with the proxy-ARP/ND function
shutdown. PEs do not intercept ARP/ND requests and flood all
requests, as in a conventional layer-2 network. While no ARP/ND
mitigation is used in this scenario, the IXP can still take advantage
of EVPN features such as control plane learning and all-active
multihoming in the peering network. Existing mitigation solutions,
such as the ARP-Sponge daemon [ARP-Sponge] MAY also be used in this
scenario.
Although this option does not require any of the procedures described
in this document, it is added as baseline/default option for
completeness.
6.2. Dynamic Learning with Proxy-ARP/ND
This scenario minimizes flooding while enabling dynamic learning of
IP->MAC entries. The Proxy-ARP/ND function is enabled in the MAC-VRFs
of the EVPN PEs, so that the PEs intercept and respond to CE
requests.
The solution MAY further reduce the flooding of the ARP/ND messages
in the EVPN network by snooping ARP/ND messages issued by the CEs.
PEs will flood requests if the entry is not in their Proxy table. Any
unknown source MAC->IP entries will be learnt and advertised in EVPN,
and traffic to unknown entries is discarded at the ingress PE.
6.3. Hybrid Dynamic Learning and Static Provisioning with Proxy-ARP/ND
Some IXPs want to protect particular hosts on the peering network
while allowing dynamic learning of peering router addresses. For
example, an IXP may want to configure static MAC->IP entries for
management and infrastructure hosts that provide critical services.
In this scenario, static entries are provisioned from the management
plane for protected MAC->IP addresses, and dynamic learning with
Proxy-ARP/ND is enabled as described in section 6.2 on the peering
network.
6.4 All Static Provisioning with Proxy-ARP/ND
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For a solution that maximizes security and eliminates flooding and
unknown unicast in the peering network, all MAC-IP entries are
provisioned from the management plane. The Proxy-ARP/ND function is
enabled in the MAC-VRFs of the EVPN PEs, so that the PEs intercept
and respond to CE requests. Dynamic learning and ARP/ND snooping is
disabled so that traffic to unknown entries is discarded at the
ingress PE. This scenario provides and IXP the most control over
MAC->IP entries and allows an IXP to manage all entries from a
management system.
6.5 Deployment Scenarios in IXPs
Nowadays, almost all IXPs installed some security rules in order to
protect the IXP-LAN. These rules are often called port security. Port
security summarizes different operational steps that limit the access
to the IXP-LAN, to the customer router and controls the kind of
traffic that the routers are allowed to be exchange (e.g., Ethernet,
IPv4, IPv6). Due to this, the deployment scenario as described in 6.4
"All Static Provisioning with Proxy-ARP/ND" is the predominant
scenario for IXPs.
In addition to the "All Static Provisioning" behavior, in IXP
networks it is recommended to configure the Reply Sub-Function to
'discard' ARP-Requests/NS messages with unrecognized options.
At IXPs, customers usually follow a certain operational life-cycle.
For each step of the operational life-cycle specific operational
procedures are executed.
The following describes the operational procedures that are needed to
guarantee port security throughout the life-cycle of a customer with
focus on EVPN features:
1. A new customer is connected the first time to the IXP:
Before the connection between the customer router and the IXP-LAN
is activated, the MAC of the router is white-listed on the IXP's
switch port. All other MAC addresses are blocked. Pre-defined IPv4
and IPv6 addresses of the IXP's peering network space are
configured at the customer router. The IP->MAC static entries
(IPv4 and IPv6) are configured in the management system of the IXP
for the customer's port in order to support Proxy-ARP/ND.
In case a customer uses multiple ports aggregated to a single
logical port (LAG) some vendors randomly select the MAC address of
the LAG from the different MAC addresses assigned to the ports. In
this case the static entry will be used associated to a list of
allowed MACs.
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2. Replacement of customer router:
If a customer router is about to be replaced, the new MAC
address(es) must be installed in the management system besides the
MAC address(es) of the currently connected router. This allows the
customer to replace the router without any active involvement of
the IXP operator. For this, static entries are also used. After
the replacement takes place, the MAC address(es) of the replaced
router can be removed.
3. Decommissioning a customer router
If a customer router is decommissioned, the router is disconnected
from the IXP PE. Right after that, the MAC address(es) of the
router and IP->MAC bindings can be removed from the management
system.
6.6 Deployment Scenarios in DCs
DCs normally have different requirements than IXPs in terms of Proxy-
ARP/ND. Some differences are listed below:
a) The required mobility in virtualized DCs makes the "Dynamic
Learning" or "Hybrid Dynamic and Static Provisioning" models more
appropriate than the "All Static Provisioning" model.
b) IPv6 'anycast' may be required in DCs, while it is not a
requirement in IXP networks. Therefore if the DC needs IPv6
'anycast' it will be explicitly enabled in the proxy-ND function,
hence the proxy-ND sub-functions modified accordingly. For
instance, if IPv6 'anycast' is enabled in the proxy-ND function,
Duplicate IP Detection must be disabled.
c) DCs may require special options on ARP/ND as opposed to the
Address Resolution function, which is the only one typically
required in IXPs. Based on that, the Reply Sub-function may be
modified to forward or discard unknown options.
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].
In this document, these words will appear with that interpretation
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only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
In this document, the characters ">>" preceding an indented line(s)
indicates a compliance requirement statement using the key words
listed above. This convention aids reviewers in quickly identifying
or finding the explicit compliance requirements of this RFC.
8. Security Considerations
When EVPN and its associated Proxy-ARP/ND function are used in IXP
networks, they only provide ARP/ND security and mitigation. IXPs MUST
still employ security mechanisms that protect the peering network and
SHOULD follow established BCPs such as the ones described in [Euro-IX
BCP].
For example, IXPs should disable all unneeded control protocols, and
block unwanted protocols from CEs so that only IPv4, ARP and IPv6
Ethertypes are permitted on the peering network. In addition, port
security features and ACLs can provide an additional level of
security.
9. IANA Considerations
No IANA considerations.
10. References
10.1. Normative References
[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>.
[RFC4861]Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI
10.17487/RFC4861, September 2007, <http://www.rfc-
editor.org/info/rfc4861>.
[RFC0826]Plummer, D., "Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet Address for
Transmission on Ethernet Hardware", STD 37, RFC 826, DOI
10.17487/RFC0826, November 1982, <http://www.rfc-
editor.org/info/rfc826>.
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[RFC6820]Narten, T., Karir, M., and I. Foo, "Address Resolution
Problems in Large Data Center Networks", RFC 6820, DOI
10.17487/RFC6820, January 2013, <http://www.rfc-
editor.org/info/rfc6820>.
[RFC7342]Dunbar, L., Kumari, W., and I. Gashinsky, "Practices for
Scaling ARP and Neighbor Discovery (ND) in Large Data Centers",
RFC 7342, DOI 10.17487/RFC7342, August 2014, <http://www.rfc-
editor.org/info/rfc7342>.
[RFC3971]Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, DOI 10.17487/RFC3971,
March 2005, <http://www.rfc-editor.org/info/rfc3971>.
[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>.
[RFC5227]Cheshire, S., "IPv4 Address Conflict Detection", RFC 5227,
DOI 10.17487/RFC5227, July 2008, <http://www.rfc-
editor.org/info/rfc5227>.
10.2. Informative References
[ARP-Sponge] Wessel M. and Sijm N., Universiteit van Amsterdam,
"Effects of IPv4 and IPv6 address resolution on AMS-IX and the ARP
Sponge", July 2009.
[EVPN-ND-FLAGS] Sathappan S., Nagaraj K. and Rabadan J., "Propagation
of IPv6 Neighbor Advertisement Flags in EVPN", draft-snr-bess-evpn-
na-flags-02, Work in Progress, July 2015.
[Euro-IX BCP] https://www.euro-ix.net/pages/28/1/bcp_ixp.html
11. Acknowledgments
The authors want to thank Ranganathan Boovaraghavan, Sriram
Venkateswaran, Manish Krishnan, Seshagiri Venugopal, Tony Przygienda
and Robert Raszuk for their review and contributions. Thank you to
Oliver Knapp as well, for his detailed review.
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Authors' Addresses
Jorge Rabadan (Editor)
Alcatel-Lucent
777 E. Middlefield Road
Mountain View, CA 94043 USA
Email: jorge.rabadan@alcatel-lucent.com
Senthil Sathappan
Alcatel-Lucent
Email: senthil.sathappan@alcatel-lucent.com
Kiran Nagaraj
Alcatel-Lucent
Email: kiran.nagaraj@alcatel-lucent.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Greg Hankins
Alcatel-Lucent
Email: greg.hankins@alcatel-lucent.com
Thomas King
DE-CIX Management GmbH
Lichtstrasse 43i, Cologne 50825, Germany
Email: thomas.king@de-cix.net
Daniel Melzer
DE-CIX Management GmbH
Lichtstrasse 43i, Cologne 50825, Germany
Email: daniel.melzer@de-cix.net
Erik Nordmark
Arista Networks
Email: nordmark@arista.com
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