3Com Router User Manual

							Displaying and Debugging VRRP657
Configure Standby 
Group TimerThe master router of a VRRP standby group notifies its normal operation state to 
the routers within the group by sending them VRRP packets regularly 
(adver_interval).
 If the backup routers fail to receive the VRRP packets over a 
certain period of time (master_down_interval), they reach the conclusion that the 
master routers are not functioning properly and will change their own state to 
master.
The user can adjust the master routers sending interval (adver_interval) of VRRP 
packets by configuring the timer command. The master_down_interval of the 
backup routers are three times that of the adver_interval. Too much network 
traffic or the differences of different router timers will result in abnormal 
master_down_interval and state switchover. Such problems can be solved through 
prolonging the adver_interval and configuring delay time.
Perform the following configuration in interface view:
Ta b l e 708   Configure VRRP Timer
By default adver_interval is set 1 seconds, namely, the default value of 
adver_interval is 1 second, while the default value of master_down_interval is 3 
seconds. 
Monitoring the 
Specified InterfaceThe interface monitoring function of VRRP expands backup function: when the 
interface of the router is unavailable, it is regarded that the router is not stable, 
hence it should not act as a master router. After the interface monitoring function 
is set, the routers priority will be adjusted dynamically according to the state of 
the interface that is under monitoring. Once the monitored interface becomes 
unavailable, the priority value of this router is reduced, so that another router with 
a more stable interface state in the same backup group can act as a master router 
more easily
Perform the following configuration in Ethernet interface view:
Ta b l e 709   Configure Monitoring Interface
By default interface-priority is 10.
Displaying and 
Debugging VRRPPerform the display and debugging commands in all views.
OperationCommand
Configure VRRP timervrrp vrid virtual_router_id 
timer-advertise seconds
Restore the default value of VRRP timerundo vrrp vrid virtual_router_id 
timer-advertise
OperationCommand
Set to monitor the specified interfacevrrp vrid virtual_router_id track 
interface_type interface_number [ 
reduced priority ]
Cancel the monitoring of the specified 
interfaceundo vrrp vrid virtual_router_id 
track interface_type 
interface_number 
						

							658CHAPTER 46: CONFIGURING VRRP
Ta b l e 710   Display and Debug VRRP
VRRP Configuration 
ExamplesThis section describes several different configurations of VRRP with a suggested 
procedure for each configuration
VRRP Single Standby 
GroupHost A uses the VRRP standby group which combines router A and router B as its 
default gateway to visit host B on the Internet.
A VRRP standby group consists of the following parts: standby group number1, 
virtual IP address 202.38.160.111, router A as the MASTER and router B as the 
backup with preemption a
II. Networking diagram
Figure 209   VRRP application illustration
1Configure router A:
[Router-Ethernet0] vrrp vrid 1 virtual-ip 202.38.160.111
[Router-Ethernet0] vrrp vrid 1 priority 120
2Configure router B:
[Router-Ethernet0] vrrp vrid 1 virtual-ip 202.38.160.111
The standby group can be used immediately after configuration. The default 
gateway of host A can be set as 202.38.160.111.
Under normal conditions, router A functions as the gateway, but when router A is 
turned off or malfunctioning, router B will function as the gateway instead.
The configuration of preemption mode is aimed for router A to resume its 
gateway function as the master when it recovers.
OperationCommand
Display VRRP State Informationdisplay vrrp
Enable the debugging of VRRPdebugging vrrp { packet | state }
Host B
10.2.3.1
Host A 202.38.160.1 202.38.160.2Visual IP address
202.38.160.111
202.38.160.3
Router ARouter B
Internet 
						

							Troubleshooting VRRP659
VRRP Monitoring 
Interface As shown in Figure 209, even when router A is still functioning, it may want router 
B to function as a gateway when the Internet interface connected with it does not 
function properly. This can be implemented by configuring the monitoring 
interface.
To facilitate explanation, the standby group number is set as 1 with configuration 
of authorization key and timer added (which are unnecessary in this application).
1Configure router A:
[Router-Ethernet0] vrrp vrid 1 virtual-ip 202.38.160.111
[Router-Ethernet0] vrrp vrid 1 priority 120
[Router-Ethernet0] vrrp authentication-mode simple 3Com Router
[Router-Ethernet0] vrrp vrid 1 timer-advertise 5
[Router-Ethernet0] vrrp vrid 1 track serial0 reduced 30
2Configure router B:
[Router-Ethernet0] vrrp vrid 1 virtual-ip 202.38.160.111
[Router-Ethernet0] vrrp authentication-mode simple 3Com Router
[Router-Ethernet0] vrrp vrid 1 timer-advertise 5
Under normal conditions, router A functions as the gateway, but when the 
interface Serial0 of router A is malfunctioning, its priority will be reduced by 30, 
lower than that of router B so that router B will preempt to function as master for 
gateway services instead.
When Serial0, the interface of router A, recovers, this router will resume its 
gateway function as the master.
Multiple Standby 
Groups ConfigurationOne 3Com router is allowed to function as the standby router for many standby 
groups. See 
Figure 209.
Such a multi-backup configuration can implement load balancing. Some hosts 
(like host A) use hot standby group 1 as their gateways, some other hosts (like 
host B) use hot standby group 2 as their gateways. In this way, both data stream 
balancing and mutual backup are implemented.
1Configure router A:
[Router-Ethernet0] vrrp vrid 1 virtual-ip 202.38.160.111
[Router-Ethernet0] vrrp vrid 1 priority 120
[Router-Ethernet0] vrrp vrid 2 virtual-ip 202.38.160.112
2Configure router B:
[Router-Ethernet0] vrrp vrid 1 virtual-ip 202.38.160.111
[Router-Ethernet0] vrrp vrid 2 virtual-ip 202.38.160.112
[Router-Ethernet0] vrrp vrid 2 priority 120
Troubleshooting VRRPAs the configuration of VRRP is not very complicated, almost all the malfunctions 
can be located through checking the information of configuration and debugging. 
Explanations are made of common failures trouble-shooting in the following part. 
						

							660CHAPTER 46: CONFIGURING VRRP
The console frequently displays messages about configuration mistakes.
This shows that a mistaken VRRP packet has been received. One reason may be 
inconsistent configuration of another router within the standby group. Another 
reason may be the attempt of some devices to send out illegal VRRP packets. 
The first possibility can be solved through modifying the configuration. The second 
possibility is caused by the malicious attempt of some devices so non-technical 
measures should be attempted.
Many master routers exist within the same standby group.
There are also 2 reasons. One is short coexistence of many master routers, which is 
normal and needs no manual intervention
. Another is the long coexistence of 
many master routers, which may be caused by failure to receive VRRP packets 
between master routers, or the reception of illegal
 packets. 
To solve these problems, try to ping the many master routers. If that fails, it 
indicates faults in the links between routers and it is necessary to check the links. If 
they can be pinged through, it indicates that the problems may be caused by an 
inconsistent configuration. For the configuration of the same VRRP standby group, 
complete consistence for the number of virtual IP addresses, each virtual IP 
address, timer interval and authentication method must be guaranteed.
There is requent switchover of the VRRP state.
Such problems are generally caused by standby group timer intervals that are too 
short. To solve this problem, extend this interval or configure the preemption 
delay. 
						

							XI
QOS
Chapter 47QoS Overview
Chapter 48Traffic Policing, Traffic Shaping and Line Rate
Chapter 49Congestion Management
Chapter 50Congestion Avoidance 
						

							662 
						

							47
QOS OVERVIEW
This chapter covers the following topics:
■What Is QoS?
■Three Types of QoS Services
■Benefits of QoS for the Network Service
What Is QoS?In the traditional IP network, all the packets are treated identically. Each router has 
to handle these packets a following first in first out (FIFO) policy. That is, it makes 
best effort to transmit the packets to the destination without considering the 
throughput, delay, jitter, drop rate of the packets, etc. This may be advantageous 
or disadvantageous, depending on the conditions of the network. With the rapid 
development of the computer networks, the voice, image, and important data 
that are sensitive to the bandwidth, delay and jitter are simultaneously transmitted 
over the network, which enrich the network resources. However, at the same 
time, there are more strict requirements for the network transmission data quality. 
They expect that a certain service guarantee in terms of the throughput, delay, 
delayed jitter, and packet loss ratio of the packets can be obtained, and that 
different services may be provided on the basis of the client types. One way to 
solve these problems is to increase the bandwidth of the network, however, the 
increase in bandwidth is so limited and so expensive that it only relieves this 
problem to some extent. The provision of QoS is the basic requirements for future 
IP networks.
Quality of Service (QoS) refers to a series of technology integrations to obtain the 
expected service level with respect to the throughput, delayed jitter, delay, and 
packet loss ratio for users. In short, QoS is the network service that provides 
different service qualities that meet various kinds of demands.
Three Types of QoS 
ServicesGenerally, the services of QoS are usually divided into the following three types:
■Best-effort service: This is the default service model provided by IP. It uses a 
FIFO (first in, first out) queue, offers the most primitive service of 
routing-forwarding, and provides no guarantee for delay and reliability. It 
can satisfy most early networks requirement (e.g., FTP, E-mail), but cannot 
provide high quality services for the developing voice and multimedia services.
■Integrated service: This model is usually applied on the edge routers. In this 
model, before sending a packet, it is necessary to apply for network resource 
and service quality through signal. After the confirmation of Resource 
Reservation Protocol (RSVP), the packets can be sent, and the size of the traffic 
is not larger than the preset traffic parameters. 
						

							664CHAPTER 47: QOS OVERVIEW
■Differentiated service: This is is a kind of multi-service model oriented to 
different demands. It sorts the services into classes, and provides different 
qualities of services according to the various classes without the support of 
signal. Differentiated service adopts the following technologies:
■Traffic policing: Performing the traffic policing for one or more or all flows.
■Traffic shaping: Performing the traffic shaping for one or more or all flows.
■Queue management: Performing congestion management for the queues 
on the interface by employing the technologies such as FIFO, Priority Queue 
(PQ), Customized Queue (CQ), Weighted Fair Queue (WFQ), Class-based 
Weighted Fair Queue (CBWFQ).
■Congestion avoidance: It is a traffic control mechanism that, by monitoring 
the usage of the network resources (such as the queue or memory buffer), 
removes the network overload by dropping packets on its own initiative to 
adjust the network traffic in case of network congestion.
The QoS of the 3Com router is implemented based on the differentiated service, 
and has the following functions:
■Packet classification: The services with different service quality requirements 
are classified in the network edge. It is processed according to different packet 
classifications in the core network.
■Traffic policing: Two token buckets are used to indicate the allowable burst 
levels.  Tokens are placed into each bucket at the same rate (CIR).  The CBS (the 
C bucket) is generally smaller than EBS (the E bucket).  When traffic 
conformance is being evaluated,  if the C bucket has sufficient tokens, the 
traffic is said to conform to allowable burst levels.  If the C Bucket is short of 
tokens but the E bucket has sufficient tokens, the traffic partially conforms to 
allowable burst levels.  If  both the C and E buckets are short of tokens,  the 
traffic does not conform to the allowable burst levels.
■Traffic shaping: Performs the shaping on the flows that do not conform to 
the predetermined traffic characteristics, to facilitate the bandwidth matching. 
It may perform the shaping on each flow or all flows on the interface.
■Interface Line Rate: Provides a management approach to the network 
bandwidth by limiting the physical interface bandwidth.
■Congestion management: Provides various queue mechanisms to relieve and 
dispatch the congested packets when the interface congestion occurs.
■Congestion avoidance: Takes measures to avoid the congestion by estimating 
the congestion status of the network. The congestion avoidance may reduce 
the packet loss ratio and improve the efficiency of the network availability.
Benefits of QoS for 
the Network ServiceQoS can provide controllable and predictable services for network applications and 
network traffic. Using QoS in the network can realize:
■Control of network resources. The user can control the usage of network 
resources. For example, the user may limit the bandwidth resource consumed 
in the FTP transmission on a connection, or provide higher priority for the data 
that are more important. 
						

							Benefits of QoS for the Network Service665
■Adjustable network service. If the user is ISP, by using QoS, the adjustable 
network services of different priority levels can be provided to various types of 
clients.
■Secure network services for specific data flows. For example, it can ensure that 
the multimedia data flows and voice flows sensitive to the delay will acquire 
the service in time. 
						

							666CHAPTER 47: QOS OVERVIEW