Internet DRAFT - draft-ietf-bess-virtual-subnet-fib-reduction
draft-ietf-bess-virtual-subnet-fib-reduction
Network Working Group X. Xu
Internet-Draft Huawei
Intended status: Informational C. Jacquenet
Expires: September 1, 2016 Orange
T. Boyes
Bloomberg LP
B. Fee
Extreme Networks
W. Henderickx
Alcatel-Lucent
February 29, 2016
FIB Reduction in Virtual Subnet
draft-ietf-bess-virtual-subnet-fib-reduction-02
Abstract
Virtual Subnet is a BGP/MPLS IP VPN-based subnet extension solution
which is intended for building Layer3 network virtualization overlays
within and/or between data centers. This document describes a
mechanism for reducing the FIB size of PE routers in the Virtual
Subnet context.
Status of This Memo
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This Internet-Draft will expire on September 1, 2016.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Solution Description . . . . . . . . . . . . . . . . . . . . 3
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Virtual Subnet [I-D.ietf-bess-virtual-subnet] is a BGP/MPLS IP VPN
[RFC4364] -based subnet extension solution which is intended for
building Layer3 network virtualization overlays within and/or across
data centers. In the Virtual Subnet context, since CE host routes of
a given VPN instance need to be exchanged among PE routers
participating in that VPN instance, the resulting forwarding table
(a.k.a. FIB) size of PE routers may become a big concern in large-
scale data center environment where they may need to install a huge
amount of host routes into their forwarding tables. In some cases
where host routes need to be maintained on the control plane, it
needs a method to reduce the FIB size of PE routers without any
change to the RIB and the routing table. Therefore, this document
proposes a very simple mechanism for reducing the FIB size of PE
routers. The basic idea of this mechanism is: Those host routes
learnt from remote PE routers are selectively installed into the FIB
while the remaining routes including local CE host routes are
installed into the FIB by default as before.
1.1. Requirements Language
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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2. Terminology
This memo makes use of the terms defined in [RFC4364].
3. Solution Description
+----------+
+----+PE/RR(APR)+----+
+------------------+ | +----------+ | +---------------_--+
|VPN_A:192.0.2.1/24| | | |VPN_A:192.0.2.1/24|
| \ | | | | / |
| +------+ \ ++---+-+ +-+---++/ +------+ |
| |Host A+------_+ PE-1 | | PE-2 +------+Host B| |
| +------+\ ++-+-+-+ +-+-+-++ /+------+ |
| 192.0.2.2/24 | | | | | | 192.0.2.3/24 |
| | | | | | | |
| DC West | | | IP/MPLS Backbone | | | DC East |
+------------------+ | | | | +------------------+
| +--------------------+ |
| |
VRF: V VRF:V
+--------------+---------+--------+------+ +--------------+---------+--------+------+
| Prefix | Nexthop |Protocol|In_FIB| | Prefix | Nexthop |Protocol|In_FIB|
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.1/32 |127.0.0.1| Direct | Yes | |192.0.2.1/32 |127.0.0.1| Direct | Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.2/32 |192.0.2.2| Direct | Yes | |192.0.2.2/32 | PE-1 | IBGP | No |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.3/32 | PE-2 | IBGP | No | |192.0.2.3/32 |192.0.2.3| Direct | Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.0/25 | APR | IBGP | Yes | |192.0.2.0/25 | APR | IBGP | Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.128/25| APR | IBGP | Yes | |192.0.2.128/25| APR | IBGP | Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
|192.0.2.0/24 |192.0.2.1| Direct | Yes | |192.0.2.0/24 |192.0.2.1| Direct | Yes |
+--------------+---------+--------+------+ +--------------+---------+--------+------+
Figure 1: Selective FIB Installation Example
To reduce the FIB size of PE routers, the selective FIB installation
concept as described in [I-D.ietf-grow-va] can be leveraged in the
Virtual Subnet context. Take the VPN instance demonstrated in
Figure 1 as an example, the FIB reduction procedures are described as
follows:
1. Multiple more specific prefixes (e.g., 192.0.2.0/25 and
192.0.2.128/25) corresponding to an extended subnet (i.e.,
192.0.2.0/24) are specified as Virtual Prefixes (VPs).
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Meanwhile, one or more PE routers (or route reflectors) are
configured as Aggregation Point Routers (APR) for each VP. The
APRs for a given VP would install a null route to that VP while
propagating a route to that VP via the L3VPN signaling.
2. For a given host route in the routing table which is learnt from
any remote PE router, PE routers which are non-APRs for any VP
covering this host route would not install it into the FIB by
default. In contrast, PE routers (or route reflectors) which are
APRs for any VP covering that host route would install it into
the FIB. If one or more particular remote host routes need to be
installed by non-APR PE routers by default as well for whatever
reasons, the best way to realize such goal is to attach a special
extended communities attribute to those particular host routes
either by originating PE routers or by route reflectors. Upon
receiving any host routes attached with the above extended
communities attribute, non-APR PE routers SHOULD install them by
default.
3. Upon receiving a packet destined for a given remote CE host, if
no host route for that CE host is found in the FIB, the ingress
PE router would forward the packet to a given APR according to
the longest-matching VP route, which in turn forwards the packet
to the final egress PE router. In this way, the FIB size of
those non-APR PE routers can be greatly reduced at the potential
cost of path stretch.
In order to forward packets destined for remote CE hosts directly to
the final egress PE routers without the potential path stretch
penalty, non-APR PE routers could perform on-demand FIB installation
for remote host routes which are available in the routing table. For
example, upon receiving an ARP request or Neighbor Solicitation (NS)
message from a local CE host, the non-APR PE router would perform a
lookup in the routing table. If a corresponding host route for the
target host is found but not yet installed into the FIB, it would be
installed into the FIB. Another possible way to trigger on-demand
FIB installation is as follows: when receiving a packet whose
longest-matching FIB entry is a particular VP route learnt from any
APR, a copy of this packet would be sent to the control plane while
this original packet is forwarded as normal. The above copy sent to
the control plane would trigger a lookup in the routing table. If a
corresponding host route is found but not yet installed into the FIB,
it would be installed into the FIB. To provide robust protection
against DoS attacks on the control plane, rate-limiting of the above
packets sent to the control plane MUST be enabled. Those FIB entries
for remote CE host routes which are on-demand installed on non-APR PE
routers would expire if not used for a certain period of time.
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4. Acknowledgements
The authors would like to thank Susan Hares, Yongbing Fan, Robert
Raszuk and Bruno Decraene for their valuable suggestions on this
document.
5. IANA Considerations
The type value for the Extended Communities Attributes as described
in this doc is required to be allocated by the IANA.
6. Security Considerations
Those security considerations as described in
[I-D.ietf-bess-virtual-subnet] are applicable to this document. This
document does not introduce any new security risk.
7. References
7.1. Normative References
[I-D.ietf-bess-virtual-subnet]
Xu, X., Jacquenet, C., Raszuk, R., Boyes, T., and B. Fee,
"Virtual Subnet: A BGP/MPLS IP VPN-based Subnet Extension
Solution", draft-ietf-bess-virtual-subnet-07 (work in
progress), December 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <http://www.rfc-editor.org/info/rfc4364>.
7.2. Informative References
[I-D.ietf-grow-va]
Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
L. Zhang, "FIB Suppression with Virtual Aggregation",
draft-ietf-grow-va-06 (work in progress), December 2011.
Authors' Addresses
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Xiaohu Xu
Huawei
Email: xuxiaohu@huawei.com
Christian Jacquenet
Orange
Email: christian.jacquenet@orange.com
Truman Boyes
Bloomberg LP
Email: tboyes@bloomberg.net
Brendan Fee
Extreme Networks
Email: bfee@enterasys.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
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