FIB Reduction in Virtual Subnet
draft-xu-l3vpn-virtual-subnet-fib-reduction-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Xiaohu Xu , Susan Hares , Fan Yongbing , Christian Jacquenet , Truman Boyes , Brendan Fee | ||
| Last updated | 2014-02-14 | ||
| Replaced by | draft-ietf-bess-virtual-subnet-fib-reduction | ||
| RFC stream | (None) | ||
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| Consensus boilerplate | Unknown | ||
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draft-xu-l3vpn-virtual-subnet-fib-reduction-00
Network working group X. Xu
Internet Draft Huawei
Category: Informational
S. Hares
Y. Fan
China Telecom
C. Jacquenet
Orange
T. Boyes
Bloomberg LP
B Fee
Extreme Networks
Expires: August 2014 February 14, 2014
FIB Reduction in Virtual Subnet
draft-xu-l3vpn-virtual-subnet-fib-reduction-00
Abstract
Virtual Subnet is a L3VPN-based subnet extension solution which can
be used to build Layer3 network virtualization overlays within and/or
across data centers. This document describes a mechanism for reducing
the FIB size of PE routers in the Virtual Subnet context.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Draft FIB Reduction in Virtual Subnet February 2014
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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].
Table of Contents
1. Introduction ................................................ 3
2. Solution Overview ........................................... 3
3. Security Considerations ..................................... 5
4. IANA Considerations ......................................... 5
5. Acknowledgements ............................................ 5
6. References .................................................. 5
6.1. Normative References ................................... 5
6.2. Informative References ................................. 5
Authors' Addresses ............................................. 5
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1. Introduction
Virtual Subnet [VS] is a L3VPN-based subnet extension solution which
can be used to build Layer3 network virtualization overlays within
and/or across data centers. Since host routes of a given VPN instance
are usually exchanged among PE routers participating in that VPN
instance in the context of Virtual Subnet, the forwarding table
(a.k.a. FIB) size of PE routers may become a scaling concern once
they need to install a huge amount of host routes into their
forwarding tables, especially in the particular cloud data center
interconnect scenario where millions of host routes are there.
To address the above FIB scaling concern, 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 installed into the FIB on demand, while the remaining
routes including local host routes are installed into the FIB by
default as before.
2. Solution Overview
+--------+
+-----+PE-3/APR+-----+
+-----------------+ | +--------+ | +-----------------+
|VPN_A:1.1.1.1/24 | | | |VPN_A:1.1.1.1/24 |
| \ | | | | / |
| +------+ \++---+-+ +-+---++/ +------+ |
| |Host A+------+ PE-1 | | PE-2 +------+Host B| |
| +------+\ ++-+-+-+ +-+-+-++ /+------+ |
| 1.1.1.2/24 | | | | | | 1.1.1.3/24 |
| | | | | | | |
| DC West | | | IP/MPLS Backbone | | | DC East |
+-----------------+ | | | | +-----------------+
| +--------------------+ |
| |
VRF_A : V VRF_A : V
+------------+---------+--------+------+ +------------+---------+--------+------+
| Prefix | Nexthop |Protocol|In_FIB| | Prefix | Nexthop |Protocol|In_FIB|
+------------+---------+--------+------+ +------------+---------+--------+------+
| 1.1.1.1/32 |127.0.0.1| Direct | Yes | | 1.1.1.1/32 |127.0.0.1| Direct | Yes |
+------------+---------+--------+------+ +------------+---------+--------+------+
| 1.1.1.2/32 | 1.1.1.2 | Direct | Yes | | 1.1.1.2/32 | PE-1 | IBGP | No |
+------------+---------+--------+------+ +------------+---------+--------+------+
| 1.1.1.3/32 | PE-2 | IBGP | No | | 1.1.1.3/32 | 1.1.1.3 | Direct | Yes |
+------------+---------+--------+------+ +------------+---------+--------+------+
| 1.1.1.0/25 | APR | IBGP | Yes | | 1.1.1.0/25 | APR | IBGP | Yes |
+------------+---------+--------+------+ +------------+---------+--------+------+
|1.1.1.128/25| APR | IBGP | Yes | |1.1.1.128/25| APR | IBGP | Yes |
+------------+---------+--------+------+ +------------+---------+--------+------+
| 1.1.1.0/24 | 1.1.1.1 | Direct | Yes | | 1.1.1.0/24 | 1.1.1.1 | Direct | Yes |
+------------+---------+--------+------+ +------------+---------+--------+------+
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Figure 1: FIB Reduction Example
To reduce the FIB size of PE routers, the selective FIB installation
concept as described in [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., 1.1.1.0/25 and 1.1.1.128/25)
corresponding to an extended subnet (i.e., 1.1.1.0/24) are
specified as Virtual Prefixes (VPs). Meanwhile, one or more PE
routers 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 which are APRs for any VP covering
that host route would install it into the FIB.
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
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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.
3. Security Considerations
This document doesn't introduce additional security risk to BGP/MPLS
IP VPN, nor does it provide any additional security feature for
BGP/MPLS IP VPN.
4. IANA Considerations
There is no requirement for any IANA action.
5. Acknowledgements
Thanks Robert Raszuk for his review and suggestions on this document.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[VS] Xu, X et al., "Virtual Subnet: A L3VPN-based Subnet Extension
Solution", draft-xu-l3vpn-virtual-subnet-03 (Work in
Progress), January 2014.
6.2. Informative References
[RFC4364] Rosen. E and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[VA] Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and
L. Zhang, "Virtual Aggregation", draft-ietf-grow-va-05.txt,
(Work in Progress), December 2011.
Authors' Addresses
Xiaohu Xu
Huawei Technologies,
Beijing, China.
Phone: +86 10 60610041
Email: xuxiaohu@huawei.com
Susan Hares
Email: shares@ndzh.com
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Yongbing Fan
Guangzhou Institute, China Telecom
Guangzhou, China.
Phone: +86 20 38639121
Email: fanyb@gsta.com
Christian Jacquenet
Orange
Rennes France
Email: christian.jacquenet@orange.com
Truman Boyes
Bloomberg LP
Phone: +1 2126174826
Email: tboyes@bloomberg.net
Brendan Fee
Extreme Networks
9 Northeastern Blvd.
Salem, NH, 03079
Email: bfee@enterasys.com
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