Network working group Qiang Zhang
Internet Draft Dacheng Zhang
Category: Standards Track
Created: October 19, 2009 Huawei Technologies Co.,Ltd
Expires: April 2010
Slave Virtual Router Redundancy Protocol (SVRRP)
draft-zhang-vrrp-svrrp-00.txt
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Abstract
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In this document, we propose a simplified VRRP protocol called the
Slave Virtual Router Redundancy Protocol (SVRRP).The design
objective of SVRRP is to specify an election protocol that
dynamically assigns responsibility for a virtual router to one of
the SVRRP routers on a LAN, which is exactly as same as that of VRRP.
However, SVRRP executions do not exchange signaling packets and need
the assistance of VRRP to perform their functionality appropriately.
This approach can be used to improve the efficiency of VRRP routers
in certain scenarios.
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...................................................2
2. Terminology....................................................3
3. Motivating Scenario............................................3
4. SVRRP..........................................................4
5. IANA Considerations............................................7
6. Acknowledgments................................................7
7. References.....................................................7
Authors' Addresses................................................8
1. Introduction
In many typical scenarios (e.g., a VRRP router supporting multiple
VLANs), a VRRP router needs to backup multiple virtual routes (VRs)
simultaneously. In order to maintain the state of a VRRP instance
(execution) for the election of a VR, the router needs to exchange
VRRP signaling packets with other routers involved in the same
selection. The bandwidth consumed by the router in transporting VRRP
signaling packets is proportional to the number of the VRs which it
supports. In order to improve the efficiency of the VRRP routers in
such scenarios, a simplified VRRP, called Slave VRRP (SVRRP) is
proposed. SVRRP need not exchange signaling messages. Actually, the
state of a SVRRP instance is determined by another VRRP instance
(which is referred to as a MVRRP instance in this case). Therefore,
a VRRP router executing SVRRP needs in addition to execute MVRRP.
This solution is based on the fact that the states of a set of VRRP
instances located on a VRRP router are always identical and
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transferred in a synchronized way, e.g., when they share a same
physical interface.
2. Terminology
MVRRP Router: a router running the Management Virtual Router
Redundancy Protocol.
SVRRP Router: a router running the Slave Virtual Router Redundancy
Protocol.
VRRP instance: a VRRP execution on a router for the backup of a
virtual router.
MVRRP instance: a MVRRP execution on a router for the backup of a
virtual router.
SVRRP instance: a SVRRP execution on a router for the backup of a
virtual router.
VRRP backup group (VRRP BG): a collection of VRRP instances for the
backup of a same virtual router.
MVRRP backup group (MVRRP BG): a collection of MVRRP instances for
the backup of a same virtual router.
SVRRP backup group (SVRRP BG): a collection of SVRRP instances for
the backup of a same virtual router.
Broadcast_Timer: a global timer that fire to trigger sending
gratuitous ARP for SVRRP instances in Master.
Broadcast_interval: the interval of a Broadcast_Timer, default is
300 seconds.
3. Motivating Scenario
Figure 1 illustrates a motivating scenario where multiple hosts
belonging to different VLANs connect to two VRRP routers (Router1
and Router2) through a switch. The packets from the hosts are routed
to a same physical interface (e.g., Interface1) of the master VRRP
router (e.g., Router1). Moreover, the physical interface is divided
into multiple sub-interfaces; each is used to deal with the packets
in a VLAN.
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Because in principle a VR acts as a default router for hosts on a
shared LAN, each of the routers should generate a VRRP instance for
every VLAN respectively. As mentioned previously, a VRRP instance
needs to maintain a state machine and periodically exchange
signaling packets with others in the same VRRP back group. When the
number of VRRP instances supported by a VRRP router is large, the
resource ( e.g, bandwidth, CPU, memory )occupied in transporting and
processing signaling packets may influence the performance of the
router negatively.
+--------+
| host1 +------------\
+--------+ |
VLAN1 |
- - - - - - | Interface1
+----------+ +---------+
| | /---------+ Router1 +----/
+--------+ | | | +---------+ |
| host2 +-----------| switch +-----| |
+--------+ | | | |-----
. | | | |
. +----------+ | +---------+ |
- - - - - - | \---------+ Router2 +----\
VLANn | +---------+
+--------+ |
| hostn +------------/
+--------+
Figure 1. Motivating Scenario
In this scenario, all the VRs share the same physical interface; the
states of the VRRP instances located on a same VRRP router are
always identical and change in a concurrent way. Therefore, it can
be effective to select a VRRP BG as the MVRRP BG while the instances
in other VRRP BGs are implemented with SVRRP. The state of a MVRRP
instance is shared by the SVRRP instances on the same VRRP router,
and any change in the state of the MVRRP instance can trigger
identical changes in the states of the corresponding SVRRP instances.
Therefore, Router1 and Router2 only need to exchange VRRP signaling
packets for the MVRRP BG, irrespective of how may VRs they are
supporting.
4. SVRRP
4.1. State Transition Diagram
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+---------------+
+--------->| |<-------------+
| | Initialize | |
| +------| |----------+ |
| | +---------------+ | |
| | | |
| V V |
+---------------+ +---------------+
| |---------------------->| |
| Master | | Backup |
| |<----------------------| |
+---------------+ +---------------+
4.2. State Descriptions
In the state descriptions below, the state names are identified by
{state-name}, and the packets are identified by all upper case
characters.
There are two key events in the SVRRP state machine, the Startup
event and the Shutdown event. A Startup event arises when the
associated interface is available and the associate MVRRP instance
is in the {Backup} or the {Master} state. A Shutdown event arises
when the interface is unavailable or the associated MVRRP instance
is in the {Initialize} state.
4.2.1. Initialize
A SVRRP instance in this state just waits for a Startup event. If a
Startup event is received, then:
- If State of MVRRP is {Master}
- If broadcast_timer is inactive, then:
o set broadcast_timer to broadcast_interval.
endif
o Broadcast a gratuitous ARP request containing the virtual
router MAC address for each IP address associated with the
virtual router.
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o Transition to the {Master} state.
else
o Transition to the {Backup} state
endif
4.2.2. Backup
While in this state, MUST discard ADVERTISEMENT received.
- If receiving a Shutdown event:
o Transition to the {Initialize} state
endif
- If the state of the associated MVRRP instance is transferred
into Master. then:
o Broadcast a gratuitous ARP request containing the virtual
router MAC address for each IP address associated with the
virtual router.
o Transition to the {Master} state
endif
4.2.3. Master
While in this state, a SVRRP instance must discard the received
ADVERTISEMENT packets and periodically send gratuitous ARP packets
according to Broadcast_timer in order to update a cache of MAC
address of switch and/or hosts.
- If a Shutdown event is received, then:
o Transition to the {Initialize} state
endif
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- If the state of the associated MVRRP instance is transferred
into Backup, then:
o Transition to the {Backup} state
endif
- If the Broadcast_timer fires, then:
o Broadcast a gratuitous ARP request containing the virtual
router MAC address for each IP address associated with the
virtual router.
endif
5. IANA Considerations
No such considerations.
6. Acknowledgments
Thank Peter Smith for his kindly revision and precious comments.
7. References
[RFC3768] R. Hinden, Ed., " Virtual Router Redundancy Protocol
(VRRP)", RFC 3768, April 2004.
[RFC2338] S. Knight, D. Weaver, D. Whipple, R. Hinden, D. Mitzel, P.
Hunt, P. Higginson, M. Shand, A. Lindem, " Virtual Router Redundancy
Protocol" RFC 2338, April 1998.
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Authors' Addresses
Qiang Zhang
Huawei Technologies Co.,Ltd
Huihong Building, No.91 Baixia Rd.,
Baixia District
Nanjing, 210001
P.R. China
Email: njzq@huawei.com
Dacheng Zhang
Huawei Technologies Co.,Ltd
KuiKe Building, No.9 Xinxi Rd.,
Hai-Dian District
Beijing, 100085
P.R. China
Email: zhangdacheng@huawei.com
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