BESS Working Group S. Kumar
Internet-Draft D. Kakrania
Intended status: Standards Track V. Duna
Expires: July 16, 2017 Juniper Networks
January 12, 2017
EVPN ACCESS SECURITY
draft-surajk-evpn-access-security-00
Abstract
The draft defines a new BGP EVPN route message for syncing DHCP
packet contents as well as snoop entry among PEs in an Ethernet
Segment (ES). The snoop entry is required to implement Dynamic ARP
inspection (DAI), IP Source Guard (IPSG/IPSGv6) and IPv6 Neighbor
Discovery Inspection (NDI) access security features.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Access Security Features . . . . . . . . . . . . . . . . . . 3
3.1. DHCP snooping . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Dynamic ARP inspection (DAI) . . . . . . . . . . . . . . 3
3.3. IP Source Guard (IPSGv4/IPSGv6) . . . . . . . . . . . . . 4
3.4. IPv6 Neighbor Discovery Inspection (NDI) . . . . . . . . 4
4. DHCP Snooping Database . . . . . . . . . . . . . . . . . . . 4
4.1. CE Connected to Single PE . . . . . . . . . . . . . . . . 5
4.2. CE Connected to Multiple PEs . . . . . . . . . . . . . . 5
5. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Centralized Mode . . . . . . . . . . . . . . . . . . . . 7
5.2. Distributed Mode . . . . . . . . . . . . . . . . . . . . 7
6. DHCP Snoop Advertisement route . . . . . . . . . . . . . . . 8
6.1. Constructing DHCP Snoop Advertisement route . . . . . . . 9
7. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
In EVPN solution where a CE is connected to multiple PEs in All-
Active redundancy mode then to support Dynamic ARP inspection (DAI),
IP Source Guard (IPSG/IPSGv6) and IPv6 Neighbor Discovery Inspection
(NDI) access security features, each PE in the ES needs to build an
identical snoop database. This requires exchanging DHCP packet
relevant contents as well as complete snoop entry among PEs in the
ES. The draft defines a new BGP EVPN route for this.
2. Terminology
CE: Customer Edge device, e.g., a host, router, or switch.
PE: Provider Edge device e.g switch or router.
EVI: An EVPN instance spanning the Provider Edge (PE) devices
participating in that EVPN.
Ethernet Segment (ES): When a customer site (device or network) is
connected to one or more PEs via a set of Ethernet links, then that
set of links is referred to as an 'Ethernet segment'.
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Ethernet Segment Identifier (ESI): A unique non-zero identifier that
identifies an Ethernet segment is called an 'Ethernet Segment
Identifier'
Ethernet Tag ID (ETAG ID): An Ethernet tag identifies a particular
broadcast domain, e.g., a VLAN. An EVPN instance consists of one or
more broadcast domains.
All-Active Redundancy Mode: When all PEs attached to an Ethernet
segment are allowed to forward known unicast traffic to/from that
Ethernet segment for a given VLAN, then the Ethernet segment is
defined to be operating in All-Active redundancy mode.
3. Access Security Features
3.1. DHCP snooping
DHCP snooping enables the switch (PE), to intercept DHCP messages
exchanged between untrusted host (DHCP client) and trusted DHCP
server and build an entry for untrusted host in snooping database. A
switch builds a DHCP snooping entry by extracting relevant
information from snooped DHCP packets. Similarly, a switch builds a
DHCPv6 snooping entry by extracting relevant information from snooped
DHCPv6 packets. The snoop entry holds the following information
1- Untrusted host MAC address (mac)
2- Untrusted host IP address (ip/ip6)
3- The interface(port) on which untrusted host is connected (intf)
4- Vlan in which untrusted host resides (vlan)
The entry [mac, ip, intf, vlan] is used for DAI, IPSGv4 features
Similarly, [mac, ip6, intf, vlan] is used for IPSGv6 and NDI
features.
3.2. Dynamic ARP inspection (DAI)
Dynamic ARP inspection (DAI) protects switching devices against ARP
spoofing.
DAI inspects Address Resolution Protocol (ARP) packets on the LAN and
uses the information in the DHCP snooping database on the switch to
validate ARP packets and to protect against ARP spoofing (also known
as ARP poisoning or ARP cache poisoning). ARP requests and replies
are compared against entries in the DHCP snooping database, and
filtering decisions are made based on the results of those
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comparisons. When an attacker tries to use a forged ARP packet to
spoof an address, the switch checks the sender IP and MAC source
addresses in a ARP packet sent from a host attached to an untrusted
access interface on the switch. The switch searches an entry [mac,
ipv4, intf, vlan] in the snooping database. If the entry is not
found in DHCP snooping database, the packet is dropped.
3.3. IP Source Guard (IPSGv4/IPSGv6)
Ethernet LAN switches are vulnerable to attacks that involve spoofing
(forging) of source IP addresses or source MAC addresses. These
spoofed packets are sent from hosts connected to untrusted access
interfaces on the switch.
IP source guard checks the IP source address and MAC source address
in a packet sent from a host attached to an untrusted access
interface on the switch. The switch searches for the entry [mac, ip/
ipv6, intf, vlan] in the snooping database. If the entry is not
found in DHCP snooping database, the packet is dropped.
3.4. IPv6 Neighbor Discovery Inspection (NDI)
IPv6 Neighbor Discovery Inspection protects switching devices against
ND spoofing.
NDI inspects Neighbor Discovery packets on the LAN and uses the
information in the DHCPv6 snooping database on the switch to validate
ND packets and to protect against ND spoofing. ND packets are
compared against entries in the DHCPv6 snooping database, and
filtering decisions are made based on the results of those
comparisons. When an attacker tries to use a forged ND packet to
spoof an IPv6 address, the switch checks the IPv6 source address and
MAC source address in a ND packet sent from a host attached to an
untrusted access interface on the switch. The switch searches the
entry [mac, ip6, intf, vlan] in the DHCPv6 snooping database. If the
entry is not found in database, the packet is dropped.
4. DHCP Snooping Database
A snoop database is a place holder of snoop entries. A DHCPv4 snoop
database contains DHCPv4 snoop entries. Similarly, a DHCPv6 snoop
database contains DHCPv6 entries.
A Switch (PE) does not need the complete DHCP packet to build
snooping entry. The PE needs some relevant DHCP packet contents as
mentioned in section Section 6.1 to build a snoop entry.
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4.1. CE Connected to Single PE
+----+ +----+ +-----+
| CE1|---------------| PE |----------------| CE2 |
+----+ +----+ +-----+
Figure 1
The basic process of DHCP snooping database building consists of the
following steps. These steps are mentioned here for better
understanding of the document. The scope of document is not to
explain complete snooping mechanism.
1. The host (CE1) sends a DHCPDISCOVER packet to request an IP
address.
2. The PE forwards the packet to the DHCP server (CE2).
3. The CE2 sends a DHCPOFFER packet to offer an address. If the
DHCPOFFER packet is from a trusted interface, the switching device
forwards the packet to the DHCP client.
4. The CE1 sends a DHCPREQUEST packet to accept the IP address. The
PE adds an [mac, ip, intf, vlan] entry to the database. The entry is
considered a placeholder until a DHCPACK packet is received from the
server. Until then, the IP address could still be assigned to some
other host.
5. The CE2 sends a DHCPACK packet to assign the IP address or a
DHCPNAK packet to deny the address request.
6. The PE updates the DHCP snooping database according to the type
of packet received.
7. If the switching device receives a DHCPACK packet, it updates
lease information for the [mac, ip, intf, vlan] in its database. The
entry is deleted upon expiration of lease time.
8. If the PE receives a DHCPNACK packet, it deletes the placeholder.
4.2. CE Connected to Multiple PEs
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+--------------+
| |
+----+ | | +----+ +----+
| | | | | |---| CE2| Server
/| PE1| | IP/MPLS | | PE5| +----+
/ +----+ | Network | +----+
/ | |
/ +----+ | |
+----+/ | | | |
Client | CE1|-----| PE2| | |
+----+\ +----+ | |
\ \ | |
\ \ +----+ | |
\ \| PE3| | |
\ | | | |
\ +----+ | |
\ +----+ | |
\ | PE4| | |
\| | | |
+----+ | |
| |
+--------------+
Figure 2
In Figure 2, PE1, PE2, PE3 and PE4 are in All-Active Redundancy Mode
in an Ethernet Segment. Each PE advertises BGP Ethernet Segment (ES)
route for Redundancy group discovery and also for Designated
Forwarder (DF) election. Each PE router connected to an Ethernet
Segment, advertises a BGP Ethernet Segment (ES) route that consists
of an ESI and ES-Import extended community.
In the above Figure 2, PE1, PE2, PE3 and PE4 have the same ESI value
(say ES1). PE1 advertises its ESI value in the Ethernet Segment
Route with ES-Import community set to ES1. PE2, PE3, PE4 and PE5
will receive that route but PE2, PE3, PE4 will import this route,
since they have a matching ESI value. PE5 will not import this route
since it does not have matching ESI. This ensures PE2, PE3, PE4
knows that PE1 is connected to the same CE1 host. The process is
repeated for each PE in the ES. Each PEs in the ES comes to know
about all other PEs connected to same CE1 in the same ES. The DF
election in an ES is done as specified in [RFC7432] section 8.5.
In Figure 2, to build an identical snoop database on each PEs in the
ES, each PE needs to extract relevant information from DHCP packets
exchanged between Client (CE1) and Server (CE2). But here problem is
that all DHCP packets do not go through the same PE. For an example
DHCP REQUEST can go through one of the PE say (PE1) and DHCP ACK from
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server can go through some other PE say (PE2). Since neither PE1 nor
PE2 gets all relevant information of DHCP REQUEST and ACK packets,
PE1/PE2 cannot build snooping database.
5. Solution
The draft proposes the two possible solutions for snoop entry [mac,
ip, ESI, ETAG ID] creation and synchronization among PEs in an ES in
the All-Active Redundancy Mode. Specific realizations and
implementation details (state machines or algorithms, etc.) of below
solutions are out of the scope of this document.
5.1. Centralized Mode
The PE acting as DF must be responsible for building the snoop entry
and transporting it to all non-DF PE in the ES. The DF PE must also
be responsible for withdrawing the entry locally and as well as from
all other non-DF remote PEs in the ES. The non-DF PE must neither
create nor release the snooping entry by itself. The creation and
release of entry is controlled by DF PE in the ES. The PE must use
the proposed EVPN DHCP Snoop Advertisement route for exchanging DHCP
packet contents as well as complete bindings with other PE in the ES.
When a DF PE receives a DHCP packet from CE, it consumes it locally.
When a non-DF PE receives a DHCP packet it extracts relevant
information from the packet and transport this information to DF PE
using newly proposed EVPN DHCP Snoop Advertisement route. The non-DF
PE must not consume the DHCP packet locally.
The DF PE eventually receives all the information that are required
to build snooping entry for the untrusted host. The DF PE builds
[mac, ip, ESI, ETAG ID] entry and advertise this to all the non-DF
PEs in the ES. When the DF PE releases the entry locally then it
advertises the withdrawal of the entry to all the non-DF PEs is the
ES.
5.2. Distributed Mode
In this mode, PE (DF or non-DF) must be responsible for building and
releasing entry independently. The DF PE must be responsible for
syncing snoop entry when a new non-DF PE joins the same redundancy
group. Unlike Centralized mode, in this mode each PE must release
the snoop entry upon expiration of lease time.
When a PE receives a DHCP packet it extracts relevant information
from the packet and transport this information to all other PEs in
the ES using newly proposed EVPN DHCP Snoop Advertisement route
message. Each PE in the ES eventually receives all the information
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that are required to build snooping entry for the host. Each PE in
the ES builds [mac, ip, ESI, ETAG ID] snoop entry. Each PE in the ES
also receives the relevant DHCP release packet content to release the
entry independently.
6. DHCP Snoop Advertisement route
The [RFC7432] defines a new BGP Network Layer Reachability
Information (NLRI) called the EVPN NLRI. The format of the EVPN NLRI
is as follows:
+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
Figure 3
The EVPN NLRI is carried in BGP [RFC4271] using BGP Multiprotocol
Extensions [RFC4760] with an Address Family Identifier (AFI) of 25
(L2VPN) and a Subsequent Address Family Identifier (SAFI) of 70
(EVPN). The NLRI field in the MP_REACH_NLRI/MP_UNREACH_NLRI
attribute contains the EVPN NLRI (encoded as specified above).
This [RFC7432] defines the following Route Types:
+ 1 - Ethernet Auto-Discovery (A-D) route
+ 2 - MAC/IP Advertisement route
+ 3 - Inclusive Multicast Ethernet Tag rout
+ 4 - Ethernet Segment route
This draft defines a new route (DHCP Snoop Advertisement route) The
PE uses this route message for exchanging DHCP packet contents as
well as complete bindings with other PE.
+ 5 - DHCP Snoop Advertisement route
An DHCP Snoop Advertisement route type specific EVPN NLRI consists of
the following:
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+---------------------------------------+
|RD (8 octets) |
+---------------------------------------+
|Ethernet Segment Identifier (10 octets)|
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| Packet Flags (1 octet) |
+---------------------------------------+
| Packet Type (1 octet) |
| XID (4 octets) |
+---------------------------------------+
| Lease (4 octets) |
+---------------------------------------+
| MAC Address (6 octets) |
+---------------------------------------+
| Client IP Address (4, or 16 octets) |
+---------------------------------------+
| Client Link local Address (16 octets)|
+---------------------------------------+
| Client ID Length (2 octets) |
+---------------------------------------+
| Client ID (variable length) |
+---------------------------------------+
Figure 4
6.1. Constructing DHCP Snoop Advertisement route
Packet Flags:
Packet Flags is one-byte value in the message. The flags bit is as
defined below:
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| reserved | | | | |
+--+--+--+--+--+--+--+--+
Figure 5
The least significant bit, bit 7 indicates DHCPv6 contents or DHCPv6
snoop entry. This bit is not set for DHCPv4 contents or DHCPv4 snoop
entry.
The second least significant bit, bit 6 indicates DHCPv6 Rapid commit
option is enabled.
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The third least significant bit, bit 5 indicates DHCPv6 Reply is a
NAK. DHCPv6 NAK is extracted from Status Code option of reply
packet.
The fourth least significant bit, bit 4 indicates DHCP Snoop
Advertisement route contains the snoop entry. If this bit is not set
this indicate the DHCP Snoop Advertisement route contains DHCP packet
contents.
The lease significant bits 3, 2,1 and 0 are reserved.
Packet Type:
Type of packet, e.g DHCPDISCOVER, DHCPOFFER. This is valid only when
bit 4 is not set in Packet Flags.
XID:
Transaction ID, a random number chosen by the client, used by the
client and server to associate messages and responses between a
client and a server. This is used by the client to match incoming
DHCP messages with pending requests. This is valid only when bit 4
is not set in Packet Flags.
Lease:
The period of time IP address is allocated to a client by server.
Mac Address:
Untrusted Client's source mac address
Client IP Address:
Untrusted Client's source IP address. This can be IPv4 or IPv6 based
on the Packet Type.
Client Link Local Address:
Untrusted Client's Link Local IPv6 address. This is valid only when
bit 7 in Packet Flags is set.
Client ID Length:
Length of client ID in octets. This is valid only when bit 7 in
Packet Flags is set.
Client ID:
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The Client Identifier option is used to carry a DUID. Each DHCP
client and server has a DUID. The DUID is DHCP Unique Identifier.
This may be used as key to identify the snoop entry. This filed is
valid only when bit 7 in Packet Flags is set.
The Route Distinguisher (RD) SHOULD be a Type 1 RD [RFC4364]. The
value field comprises an IP address of the PE (typically, the
loopback address) followed by a number unique to the PE
The Ethernet Tag ID:
CE's Ethernet tag value (e.g., CE VLAN ID)
7. Error Handling
The snoop database among PEs in a ES may go out of sync due to some
PE going unreachable in the ES. The solution of this problem is out
of scope of this draft.
In Centralized mode, If DF PE goes down during the process of
building snoop entry, it is possible that the untrusted host gets IP
address but no snoop entry gets created on any of the PEs in the ES
8. Security Considerations
Same security considerations as [RFC7432].
9. 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>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<http://www.rfc-editor.org/info/rfc2131>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC7209] Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
Henderickx, W., and A. Isaac, "Requirements for Ethernet
VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,
<http://www.rfc-editor.org/info/rfc7209>.
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[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<http://www.rfc-editor.org/info/rfc4760>.
[EVPN-IGMP]
Sajassi, A., "https://tools.ietf.org/html/draft-sajassi-
bess-evpn-igmp-mld-proxy-01", October 2016.
Authors' Addresses
Suraj Kumar
Juniper Networks
Elnath, Juniper Networks
Bangalore, Karnataka 560036
India
EMail: surajk@juniper.net
Deepak Kakrania
Juniper Networks
Elnath, Juniper Networks
Bangalore, Karnataka 560036
India
EMail: dkakrania@juniper.net
Vijay Kumar Duna
Juniper Networks
Elnath, Juniper Networks
Bangalore, Karnataka 560036
India
EMail: dvijay@juniper.net
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