3Com Router User Manual

							45
CONFIGURING A STANDBY CENTER
This chapter covers the following topics:
■Standby Center Overview
■Configuring the Standby Center 
■Displaying and Debugging the Standby Center
■Standby Center Configuration Examples
Standby Center 
OverviewTo enhance a networks reliability, 3Com routers provide perfect standby functions 
through the use of standby centers
■Interfaces that have standby are called main interfaces. Every physical interface 
or sub-interface on a router can serve as a main interface. A logic channel, such 
as X.25 or frame-relay virtual circuits, on any interface can also serve as a main 
interface.
■The interfaces serving as the standby for other interfaces are called standby 
interfaces. Any physical interface or logic channel on an interface of a router 
can serve as the standby interface of another interface or logic channel.
■One main interface can have several standby interfaces; if the main interface 
goes down work resumes on a standby interface, based on priority.
■Interfaces (such as ISDN BRI and ISDN PRI interfaces) that have multiple physical 
channels can provide standbys to multiple main interfaces by using dialer route.
Standby centers support the standby load sharing function. When the traffic of 
the all-active interfaces on the standby center reaches the set enable threshold, 
routers will start a standby interface with the highest priority to share the load 
with the started interfaces. When the traffic of all active interfaces on the standby 
center is less than the set disable threshold, routers close the standby interface 
with the lowest priority.
Configuring the 
Standby Center
 
Standby center configuration includes:
■Entering the View of the Main Interface
■Specifying a Standby Interface and the Priority Used by the Main Interface
■Setting the Delay Time for Switchover between Main and Standby Interface
■Setting State-judging Conditions of the Logic Channel State
■Configuring Standby Load Sharing
Entering the View of the 
Main InterfaceOn a 3Com router, not only every physical interface or sub-interfaces of the router, 
but every virtual circuit of X.25 or frame relay can work as a main interface. If the  
						

							648CHAPTER 45: CONFIGURING A STANDBY CENTER
main interface is a physical interface or sub-interface, use the following 
commands in system view to enter the view of the interface.
Ta b l e 695   Enter the View of the Main Interface
If the main interface is a virtual circuit, it should be treated differently depending 
on the type of the virtual circuit. First, specify its logic channel number in the view 
of the physical interface to which it is subordinate, then enter the corresponding 
logic channel view.
Use the following commands in the logical channel view.
Ta b l e 696   Enter the Logic Channel View
Specifying a Standby 
Interface and the 
Priority Used by the 
Main InterfaceAny physical interface or logic channel, including a virtual circuit or dialer route, 
can work as a standby interface of the main interface. 
Use the following commands in the view of the main interface.
Ta b l e 697   Specify Standby Interface and Priority Used by the Main Interface
If one main interface has multiple standby interfaces, repeat these operations. In 
addition, if the standby interface is a logic channel, the logic channel should be 
made to correspond to the actual virtual circuit or dialer route.
Please perform the following tasks in the views of the physical interface to which 
the virtual circuit or the dialer route belongs, and specify the corresponding logic 
channel number. 
Ta b l e 698   Establish a Corresponding Relation Between Logic Channel and Virtual Circuit 
or Dialer Route
OperationCommand
Enter the view of the main interfaceinterface type number
OperationCommand
Specify a logic channel number for an 
X.25 virtual circuit. (interface view)x25 map protocol address x121-address 
x.121-address logic-channel number
Specify a logic channel number for a 
frame relay virtual circuit (interface view)fr map protocol address dlci dlci 
logic-channel number
Specify a logic channel number for a dialer 
route (interface view)dialer route protocol 
next-hop-address dialer-number 
logic-channel number
Enter corresponding logic channel view. 
(system view)logic-channel number
OperationCommand
Specify a physical interface to back up the 
main interface; its priority can also be set 
here.standby interface type number [ 
priority ]
Specify a logic channel to back up the 
main interface, its priority can also be set 
here.standby logic-channel number [ 
priority ]
OperationCommand
Specify a logic channel number for X.25 
virtual circuitx25 map protocol address x121-address 
x.121-address logic-channel number 
						

							Configuring the Standby Center 649
Setting the Delay Time 
for Switchover between 
Main and Standby 
InterfaceWhen the state of the main interface changes from up to down, the system 
doesnt switch to a standby interface immediately, but waits for a preset time 
delay instead. The system switches to the standby interface only if the state of the 
main interface remains down after the delay times out. If the main interface 
recovers within the delay time, the system will not switch to the standby interface.
Ta b l e 699   Set the Delay Time for the Switchover from the Main Interface to the Standby 
Interface
By default, the delay time for the switchover from the main interface to the 
standby interface is 0 second, meaning that the switchover is instanteous.
When the state of the main interface changes from down to up, the system 
doesnt switch to the main interface immediately, but wait for a preset time delay 
instead. The system will switch back to the main interface only if the state of the 
main interface remains up after the delay time runs out; if the main interface 
restores its down state again within the delay time, the system will not switch to 
the main interface.
Perform the following configurations in the view of the backed up main interface.
Ta b l e 700   Set the Delay Time for the Switchover from the Standby Interface to the Main 
Interface
By default, the delay time for the switchover from the standby interface to the 
main interface is 0 second, meaning that the switchover is instanteous.
Setting State-judging 
Conditions of the Logic 
Channel StateWhen the main interface is a logic channel, the logic channel is regarded as down 
after a specified number of unsuccessful calls. After it switches over to the standby 
interface, regular inspections at specified time intervals must be made on the logic 
channel to check whether it has recovered.
If the main interface has multiple standby interfaces, of which one is a logic 
channel, its necessary to judge whether the logic channel is down or up before 
opening it. If it is down, open the standby interface with the second highest 
Specify a logic channel number for frame 
relay virtual circuitfr map protocol address dlci dlci 
logic-channel number
Specify a logic channel number for Dialer 
Routedialer route protocol 
next-hop-address dialer-number 
logic-channel number
OperationCommand
Set the delay time for the switchover from 
the main interface to the standby interfacestandby timer enable-delay seconds
Restore the default delay time for the 
switchover from the main interface to the 
standby interface undo standby timer enable-delay
OperationCommand
Set the delay time for the switchover from 
the standby interface to the main interfacestandby timer disable-delay seconds
Restore the default delay time for the 
switchover from the standby interface to 
the main interfaceundo standby timer disable-delay 
						

							650CHAPTER 45: CONFIGURING A STANDBY CENTER
priority; after the logic channel changes to up, its required to switch from the 
standby interface with the second highest priority to this logic channel.
Perform the following commands in the view of the logic channel.
Ta b l e 701   Set the State-judging Conditions When the Main Interface is a Logic Channel
By default, time is set to 0 and seconds is set to 1 second. 
Configuring Standby 
Load SharingConduct the following configuration under the interface view or logic channel 
view. 
Ta b l e 702   Configure Interface or Logic Channel Load Sharing
By default, the standby load sharing function of interface is not enabled.
Displaying and 
Debugging the 
Standby CenterPlease perform the following configuration in all views.
Ta b l e 703   Display and Debug Standby Center
Standby Center 
Configuration 
ExamplesThis section describes several different configurations for standby centers with a 
suggested procedure for each configuration
Standby Between 
InterfacesTake interface Serial 2 as the standby interface for interface Serial 1.
1Enter the view of Serial 1.
[Router]interface serial 1
2Set Serial 2 as its standby interface.
[Router-Serial1]standby interface serial 2
3Set the time for switchover between main and standby interfaces as 10 seconds.
[Router-Serial1]standby timer enable-delay 10
[Router-Serial1]standby timer disable-delay 10
OperationCommand
Set the condition for judging the logic channel as 
down: the logical channel is regarded as down after 
the specified number of unsuccessful calls.standby state-down times
seconds is set to make regular inspections so as to 
check whether the original logic channel has 
recovered its “up” state.standby state-up seconds
OperationCommand
Configure the standby load sharing of 
interface or logic channelstandby threshold enable-threshold 
disable-threshold
Disable the standby load sharing 
configuration of interface and logic 
channel undo standby threshold 
enable-threshold disable-threshold
OperationCommand
Turn on the standby center debuggingdebugging standby { event | packet } 
						

							Standby Center Configuration Examples651
Multiple Standby 
InterfacesTake both interfaces Serial 1 and Serial 2 as the standby interface of interface 
Serial 0, and use interface Serial 1 as a preference.
1Enter the view of Serial 0.
[Router] interface serial 0
2Set interfaces Serial 1 and Serial 2 as the standby interfaces, their priorities being 
30 and 20, respectively.
[Router-Serial0] standby interface serial 1 30
[Router-Serial0] standby interface serial 2 20
Logical Channel Standby 
InterfaceIn this example, set interface Serial 1 as the standby interface for an X.25 virtual 
circuit on interface Serial 0.
1Configure interface Serial 0 so that it encapsulates X.25 and specify its IP address 
and X.121 address.
[Router]interface serial 0
[Router-Serial0]link-protocol x25
[Router-Serial0]ip address 1.1.1.2 255.0.0.0
[Router-Serial0]x25 x121-address 1
2Match an X.25 virtual circuit on interface Serial 0 with logic channel 10.
[Router-Serial0]x25 map ip 2.2.2.3 x121-address 2 logic-channel 10
3Enter the view of logic channel 10.
[Router-Serial0]logic-channel 10
4Specify interface Serial 1 as the standby interface of this logic channel.
[Router-logic-channel10]standby interface serial 1
5Set the time interval as 10 seconds for judging the logic channel as up.
[Router-logic-channel10]standby state-up 10
Multiple Standby 
Interfaces with a Logic 
Channe
l
Take both logic channel 3 on interface Serial 1 and interface Serial 2 as the 
standby interfaces of logic channel 5 on interface Serial 0.
1Configure that interface Serial 0 encapsulates X.25 and specify its IP address and 
X.121 address.
[Router]interface serial 0
[Router-Serial0]link-protocol x25
[Router-Serial0]ip address 1.1.1.2 255.0.0.0
[Router-Serial0]x25 x121-address 1
2Match an X.25 virtual circuit on interface Serial 0 with logic channel 5.
[Router-Serial0]x25 map ip 2.2.2.3 x121-address 2 logic-channel 5
3Configure that interface Serial 1 encapsulates X.25 and specify its IP address and 
X.121 address.
[Router-Serial0]interface serial 1
[Router-Serial1]link-protocol x25
[Router-Serial1]ip address 3.3.3.4 255.0.0.0
[Router-Serial1]x25 x121-address 3
4Match logic channel 3 with an X.25 virtual circuit on interface Serial 1.
[Router-Serial1]x25 map ip 4.4.4.5 x121-address 4 logic-channel 3 
						

							652CHAPTER 45: CONFIGURING A STANDBY CENTER
5Enter the view of logic channel 5 and set logic channel 3 and interface Serial 1 as 
its standby interfaces, their priorities being 50 and 20 respectively.
[Router-Serial1]logic-channel 5
[Router-logic-channel5]standby logic-channel 3 50
[Router-logic-channel5]standby interface serial 2 20 
						

							46
CONFIGURING VRRP
This chapter covers the following topics:
■VRRP Overview
■Configuring VRRP
■Displaying and Debugging VRRP
■VRRP Configuration Examples
■Troubleshooting VRRP
VRRP OverviewVirtual Router Redundancy Protocol (VRRP) is a fault-tolerant protocol. In general, 
a default route (the next hop is 10.100.10.1) is configured for a network host so 
that packets sent by the host with destination addresses not in the local network 
segment go through the default route to Router 1 to implement communication 
between the host and the external network. When Router 1 breaks down, in this 
network segment all the hosts that regard Router 1 as the default route next-hop 
stop the communication with the external network.
Figure 207   LAN networking scheme
To solve this problem, VRRP is designed for LANs with multi-casting and 
broadcasting capabilities, such as Ethernet. VRRP combines a group of LAN routers 
including a MASTER router and several BACKUP routers into a virtual router, called 
a standby group.
PCPCPC
Router
Ethernet 10.10.100.1
Network 
						

							654CHAPTER 46: CONFIGURING VRRP
Figure 208   Virtual router diagram
This virtual router has its own IP address: 10.100.10.1 (it can be the same as the 
interface address of a router within the standby group). The routers within the 
standby group have their own IP addresses (10.100.10.2 for the master routers 
and 10.100.10.3 for the backup routers). The host within the LAN only knows the 
IP address of this virtual router but not the specific IP addresses of the master 
router and the backup router. They configure their own default routes as the IP 
address of this virtual router. Therefore, hosts within the network communicate 
with the external network through this virtual router.
 If a master router in the 
virtual group breaks down, another backup router function as the new master 
router to continue serving the host with routing to avoid interrupting the 
communication between the host and the external networks.
For the details of VRRP, refer to RFC 2338.
Configuring VRRP■Configuring VRRP includes tasks that are described in the following section:s
■Add Virtual IP AddAdding a Virtual IP Addressress
■Configuring Router Priority in a Standby Group
■Configuring Preemption Mode and Delay of Standby Group Routers
■Configuring the Authentication Method and Authentication Key
■Configure Standby Group Timer
■Monitoring the Specified Interface
Adding a Virtual IP 
AddressAdd one IP address of the standby group network-segment to this standby group 
(also called a virtual router).
Perform the following configuration in Ethernet interface view:
PCPCPC
Router
Ethernet
Router
Real IP Address:
10.10.100.3 Real IP Address:
10.10.100.2
Virtual IP Address:
10.10.100.1
MASTER
BACKUP
Network 
						

							Configuring VRRP655
Ta b l e 704   Add Virtual IP Address
The standby group numbers ranges from 1 to 255. The virtual IP address should be 
the address of the network segment where the interface resides. It can be an 
unused IP address in the network segment, or the routers own IP address. When 
the virtual IP address is the router’s own IP address, this router is called an IP 
address owner. When the first IP address is added to a standby group, the system 
establishes this standby group. Whenever this command is executed after that, the 
system only adds this address to the virtual IP address list of this standby group. 
One router interface can be added into 14 standby groups at the same time, while 
one standby group can configure up to 16 virtual IP addresses. Before performing 
other configurations for one standby group, this command must be used first to 
establish this standby group.
Multiple virtual IP addresses (multiple virtual routers) can be configured in one 
standby group. All the virtual addresses take effect at the same time, and the 
computers in the LAN can choose any of the virtual routers as their gateway. The 
undo vrrp virtual-ip form of the command can delete one existing standby 
group or delete one virtual IP address from the virtual address list on a standby 
group.
After the last virtual IP address has been deleted from the standby group, this 
standby group is also deleted. Then this standby group no longer exists on this 
interface and all the configurations of this standby group are no longer valid.
Configuring Router 
Priority in a Standby 
GroupThe status of each router in a standby group can be determined by its priority in 
VRRP. The router with the highest priority becomes the master. Those with the 
same priority are judged by comparing the master IP addresses of their interfaces.
The range of priority is 0 to 255 (the bigger the number, the higher the priority) 
with 100 as the default. However the range to be configured is from 1 to 254. 
Priority 0 is reserved for special use by the system and 255 is reserved for the IP 
address owner.
Perform the following configuration in Ethernet interface view:
Ta b l e 705   Configure Router Priority in Standby Group
The priority for IP address owners cannot be configured and it always remains 
255.
OperationCommand
Add Virtual IP Addressvrrp vrid virtual_router_id 
virtual-ip ip-address
Delete virtual IP addressundo vrrp vrid virtual_router_id 
virtual-ip [ ip-address ]
OperationCommand
Configure the priority of the standby 
groupvrrp vrid virtual_router_id priority 
priority
Restore the default value of the priorityundo vrrp vrid virtual_router_id 
priority 
						

							656CHAPTER 46: CONFIGURING VRRP
Configuring Preemption 
Mode and Delay of 
Standby Group RoutersOnce a router in the standby group becomes the master router, so long as it still 
functions properly, other routers, even configured with higher priority later, cannot 
become the master router unless they are configured with preemption mode. The 
router in preemption mode becomes the master router if it finds its own priority is 
higher than that of the present master router. Accordingly, the former master 
router becomes the backup router. 
Along with preemption mode, delay can also be configured. This delays the 
coming of the point when the backup router becomes the master router. The 
purpose for this is: in an unstable network if the backup router has not received 
the packets from the master router punctually, it will become the master router 
(failure of backup to receive the packets may be due to network congestion, not 
due to malfunction of the master router). Therefore, a delay insures the reception 
of the packet from the master router and thus avoids frequent state switches.
The default mode is preemption without delay. The delay is set in seconds, ranging 
from 1 to 255.
Perform the following configuration in Ethernet interface view:
Ta b l e 706   Configure Preemption Mode and Delay of Standby Group Routers
Configuring the 
Authentication Method 
and Authentication KeyVRRP provides simple character authentication method.
In a secure network, authentication can be configured to No, which means no 
authentication will be conducted by the router to the VRRP packets being sent 
out. And the router receiving the VRRP packets will take them as true and legal 
without any authentication. In this case no authentication key is needed.
In a network under possible security threat, the authentication method can be 
configured to simple. That means the router sending out the VRRP packets fills 
the authentication key into the VRRP packets, while the router receiving the VRRP 
packet will compare the authentication key of the packet with the locally 
configured authentication key. If they are the same, the packet will be taken as a 
true and legal one. Otherwise, it will be regarded as an illegal packet to be 
discarded. In this case, an authentication key of less than 8 bits will be configured.
Perform the following configuration in Ethernet interface view:
Ta b l e 707   Configure Authentication Method and Authentication Key
The same authentication method and authentication key should be configured for 
the standby group of an interface.
OperationCommand
Configure the preemption mode and 
delay  for standby group.vrrp vrid virtual_router_id 
preempt-mode [ timer-delay seconds ]
Delete preemption modeundo vrrp vrid virtual_router_id 
preempt-mode
OperationCommand
Configure authentication method and 
authentication keyvrrp authentication-mode simple [ key 
]
Disabled VRRP authenticationundo vrrp authentication-mode simple