Cisco Router 826 Routers Software Configuration Guide

							  
4-5
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring Low-Latency Queuing and Link Fragmentation and Interleaving
Configuration Example
The following example shows a configuration of a PPPoE client.
vpdn enable
no vpdn logging
!
vpdn-group 1
 request-dialin
  protocol pppoe
!
interface Ethernet0
 ip address 192.168.100.1 255.255.255.0
 ip tcp adjust-mss 1452
 ip nat inside
!
interface ATM0
 no ip address
 no atm ilmi-keepalive
 pvc 8/35 
  pppoe-client dial-pool-number 1
!
dsl operating-mode auto
!
interface Dialer1
ip address negotiated
ip mtu 1492
ip nat outside
encapsulation ppp
dialer pool 1
dialer-group 1
ppp authentication pap callin
ppp pap sent-username sohodyn password 7 141B1309000528
!
ip nat inside source list 101 interface Dialer1 overload
ip route 0.0.0.0.0.0.0.0 Dialer1
access-list 101 permit ip 192.168.100.0.0.0.0.255 any
Configuring Low-Latency Queuing and Link Fragmentation and 
Interleaving
Low-Latency Queuing (LLQ) provides a low-latency, strict-priority transmit queue for Voice over IP 
(VoIP) traffic. LLQ is supported on the following routers:
Cisco 826 and Cisco 836
Cisco 827, Cisco 827H, Cisco 827-4V, Cisco 831, and Cisco 837
Cisco 828
Cisco SOHO 77, Cisco SOHO 77H, Cisco SOHO 78, Cisco SOHO 91, Cisco SOHO 96, and 
Cisco SOHO 97
Link Fragmentation and Interleaving (LFI) reduces voice traffic delay and jitter by fragmenting large 
data packets and interleaving voice packets within the data fragments.  
						

							  
4-6
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring Low-Latency Queuing and Link Fragmentation and Interleaving
Configuring LLQ
Follow these steps to configure the router for LLQ:
Step 1Ensure that the voice and data packets have different IP precedence values so that the router can 
differentiate between them. Normally, data packets should have an IP precedence of 0, and voice packets 
should have an IP precedence of 5. If the VoIP packets are generated from within the router, you may set 
the IP precedence to 5 for these packets by entering the ip precedence number command in dial-peer 
voice configuration mode as follows:
a.Enter the global configuration dial-peer voice 1 voip command.
b.Enter the ip precedence 5 command.
Step 2Create an access list and a class map for the voice packets.
a.Create an access list by entering the access-list 101 permit ip any any precedence 5 command.
b.Create a class map for the voice packets by entering class-map match-all voice command.
c.Link the class map to the access list by entering the match access-group 101 command.
Step 3Create the LLQ for voice traffic.
a.Create a policy map by entering the policy-map mypolicy command.
b.Define the class by entering the class voice command.
c.Assign the priority bandwidth to the voice traffic. The priority bandwidth assigned to the voice 
traffic depends on the codec used and the number of simultaneous calls that you allow. For example, 
a G.711 codec call consumes 200 kbps; therefore, to support one G.711 voice call you would enter 
a priority 200 command.
Step 4Attach LLQ to the dialer interface.
a.Enter the global configuration interface dialer 1 command.
b.Create a service policy by entering the service-policy out mypolicy command.
NoteAttach the service policy to the dialer interface only when LFI is used. Else, the service policy must be 
attached under the PVC itself.
Configuring LFI
Follow these steps to configure the router for LFI.
NoteWhen you are configuring LFI, the data fragment size must be greater than the voice packet size; 
otherwise, the voice packets fragment and voice quality deteriorates.
Step 1Configure the dialer bandwidth. The dialer interface has a default bandwidth of 56 kbps, which may be 
less than the upstream bandwidth of your digital subscriber line (DSL) connection. You can find the 
upstream bandwidth of your DSL connection by entering the show dsl interface atm0 command in  
						

							  
4-7
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring Class-Based Traffic Shaping to Support Low Latency Queuing
dialer interface configuration mode. If you have two or more permanent virtual circuits (PVCs) sharing 
the same DSL connection, the bandwidth configured for the dialer interface must be the same as the 
bandwidth allocated to its assigned PVC.
Step 2Enable PPP multilink, and configure fragment delay and interleaving for the dialer interface. 
a.Enter the global configuration interface dialer 1 command.
b.Specify the dialer bandwidth by entering the bandwidth 640 command. The bandwidth is specified 
in kilobits per second (kbps).
c.Enter the ppp multilink command.
d.Specify PPP multilink interleaving by entering the ppp multilink interleave command.
e.Define the fragment delay by entering the ppp multilink fragment-delay 10 command.
f.Calculate the fragment size using the following formula:
fragment size = (bandwidth in kbps/ 8) * fragment-delay in milliseconds (ms)
In this case, the fragment size = (640/8) * 10, resulting in a fragment size of 800. The fragment size 
is greater than the maximum voice packet size of 200, which is G.711 20 ms. A low fragment delay 
corresponds to a fragment size that may be smaller than the voice packet size, resulting in reduced 
voice quality.
Configuring Class-Based Traffic Shaping to Support Low 
Latency Queuing
Class-based traffic shaping (CBTS) is supported on the Cisco 831 router.
CBTS can be used to control the WAN interface traffic transmission speed to match the speed of the 
attached broadband modem or of the remote target interface. CBTS ensures that the traffic conforms to 
the policies configured for it, thereby eliminating topology bottlenecks with data-rate mismatches. 
The shape average kbps and the shape peak kbps commands enable you to define traffic shaping for an 
interface.
NoteCBTS is supported on the Ethernet 1 interface.
Configuring CBTS for LLQ
Follow the steps below to configure CBTS, beginning in global configuration mode. This procedure 
shows how to create multiple traffic classes and associate them with policy maps, and then to associate 
the policy maps with a router interface. 
Step 1Define a traffic classification.
a.Enter the class-map map-name command to define a traffic classification. For example, the name 
voice could be used to specify that this is a class map for voice traffic. 
						

							  
4-8
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring Class-Based Traffic Shaping to Support Low Latency Queuing
b.Now in class configuration mode, enter the match ip precedence 5 command to match all IP voice 
traffic with a precedence of 5. Cisco Architecture for Voice, Video and Integrated Data (AVVID) 
documentation specifies a precedence value of 5 for voice-over-IP traffic.
c.Enter exit to leave class configuration mode.
Step 2Define a policy map and associated classes for low-latency queuing.
a.Enter the policy-map map-name command in global configuration mode to construct policies and 
to allocate different network resources for the defined traffic classes. The name LLQ could be used 
to specify that this is the policy map for LLQ.
b.Now in policy-map mode, define a class to handle voice traffic by entering class QOS-class-name, 
using the class-map name you defined using the class-map command in Step 1. This command 
places the router in QOS-class configuration mode.
c.Enter priority number, where number is bandwidth in kilobits per second. A value of 300, as shown 
in the example configuration, provides enough bandwidth for two G.711 voice ports. Before setting 
a priority value, see the specification for the CODEC used for voice calls.
d.Enter exit to return to policy-map configuration mode.
e.Enter class class-default to use the default class for all traffic other than voice traffic. The name 
class-default is well known, and does not have to be predefined using the class-map command.
f.Apply WFQ to non-voice traffic by entering the fair-queue command.
g.Enter exit twice to return to global configuration mode.
Step 3Define a traffic-shaping policy map.
a.Enter policy-map map-name in global configuration mode. The name shape should be used to 
indicate this map defines overall traffic shaping that is compatible with the remote transmission rate 
bandwidth.
b.Enter class class-default to associate the default class with this policy map. 
c.Set the transmission speed to be used after traffic shaping to match the speed of the broadband 
modem or remote interface by entering the shape average kbps command, where kbps is a value in 
kilobits per second.
CautionThe transmission speed entered must be less than or equal to the TX bandwidth of the DSL or 
cable modem to which the router is attached. Specifying a value greater than the modem’s TX 
bandwidth will result in the modem’s becoming congested, and the benefits of applying QOS 
might be lost.
d.Enter service-policy name to associate the LLQ policy map with the traffic-shaping policy map. If 
the map name for the low-latency queue were LLQ, then name would be LLQ.
e.Enter exit twice to return to global configuration mode.
Step 4Apply these policies to the Ethernet 1 interface.
a.Enter the interface Ethernet 1 command.
b.Apply the service policy to the Ethernet 1 interface by entering service-policy output name, where 
name matches the policy defined in the traffic-shaping policy map. If the traffic-shaping policy map 
name were shape, the service-policy name would also be shape. 
Step 5Enter end to leave router configuration mode. 
						

							  
4-9
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring Class-Based Traffic Shaping to Support Low Latency Queuing
Configuration Example
The following example shows how a Cisco router can be configured to connect to a broadband modem 
with limited bandwidth, while ensuring voice line quality. Two policy maps are configured: 
Policy map LLQ
Policy map shape
Policy map LLQ ensures that voice traffic has a strict priority queue with bandwidth of up to 300 kbps. 
The policy map shape limits the total throughput to 2.2 MBps.
!
version 12.2
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password encryption
!
hostname 831-uut
!
ip subnet-zero
!
class-map match-all voice
 match ip precedence 5
!
!
policy-map LLQ
  class voice
    priority 300
  class class-default
   fair-queue
policy-map shape
  class class-default
   shape average 2250000
   service-policy LLQ
!
interface Ethernet0
 ip address 1.7.65.11 255.255.0.0
!
interface Ethernet1
 ip address 192.168.1.101 255.255.255.0
service-policy output shape
!
ip classless
ip http server
ip pim bidir-enable
!
line con 0
 stopbits 1
line vty 0 4
 login
!
!
scheduler max-task-time 5000
end
! 
						

							  
4-10
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring the Length of the PVC Transmit Ring
Configuring the Length of the PVC Transmit Ring
The length of the PVC transmit ring can be configured on the following Cisco routers:
Cisco 826 and Cisco 836
Cisco 827, Cisco 827H, Cisco 827-4V, and Cisco 837
Cisco 828
Cisco SOHO 77, Cisco SOHO 77H, Cisco SOHO 78, Cisco SOHO 96, and Cisco SOHO 97
If both voice and data packets share the same PVC, it is important to reduce the PVC transmit (TX) ring 
size. This reduces the maximum number of data packets and fragments that can be in front of a voice 
packet in the hardware queue, thus reducing latency.
Follow these steps to reduce the PVC TX ring size:
Step 1Enter the global configuration int atm 0 command.
Step 2Specify the PVC number by entering the pvc 1/100 command.
Step 3Reduce the PVC TX ring size to 3 by entering the tx-ring-limit 3 command.
Configuration Example
The following example combines LFI, LLQ, and the PVC TX ring configurations.
class-map match-all voice
match access-group 101
!
policy-map mypolicy
 class voice
  priority 200 
 class class-default
  fair-queue
!
interface Ethernet0
ip address 70.0.0.1 255.255.255.0
no ip mroute-cache
!
interface ATM0
 no ip address
 bundle-enable
 dsl operating-mode auto
!
interface ATM0.1 point-to-point
 no ip mroute-cache
 pvc 1/40 
 encapsulation aal5mux ppp dialer
 dialer pool-member 1
 tx-ring-limit 3
!
interface Dialer1
 bandwidth 640
 ip address 60.0.0.1 255.255.255.0
 encapsulation ppp
 dialer pool 1
 service-policy output mypolicy
 ppp multilink 
						

							  
4-11
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring DHCP Server Import
 ppp multilink fragment-delay 10
 ppp multilink interleave
!
ip classless
no ip http server
!
access-list 101 permit ip any any precedence 5
!
voice-port 1
!
voice-port 2
!
voice-port 3
!
voice-port 4
dial-peer voice 110 pots
 destination-pattern 1105555
 port 1
!
dial-peer voice 210 voip
 destination-pattern 2105555
 session target ipv4:60.0.0.2
 codec g711ulaw
 ip precedence 5
Configuring DHCP Server Import
This feature is supported on the following Cisco routers:
Cisco 826 and Cisco 836
Cisco 827, Cisco 827H, Cisco 827-4V, and Cisco 837
Cisco 828
Cisco 831
Cisco SOHO 77, Cisco SOHO 77H, Cisco SOHO 78, Cisco SOHO 91, Cisco SOHO 96, and 
Cisco SOHO 97
Before Cisco IOS Release 12.1(5), the only way to configure the DHCP options on the Cisco IOS DHCP 
server was through the command-line interface (CLI). However, you may not want to configure the same 
DHCP options on multiple DHCP servers if you can, instead, configure a remote master DHCP server 
located on the corporate backbone. In this case, all the local DHCP servers will have the same DHCP 
options as those configured on the remote DHCP server. 
The Cisco IOS DHCP server has been enhanced to allow configuration information to be updated 
automatically by PPP. You can enable PPP to automatically configure the Domain Name System (DNS) 
server, the Windows Information Name Server (WINS), or the NetB Cisco IOS Name Service (NBNS), 
and the server IP address information within a Cisco IOS DHCP server pool.
Follow these steps to configure the Cisco router for DHCP server import:
Step 1Configure the asynchronous transfer mode (ATM) interface and the asymmetric digital subscriber line 
(ADSL) operating mode.
Step 2Create an ATM PVC for data traffic, enter virtual circuit configuration mode, and specify the virtual 
path identifier/virtual channel identifier (VPI /VCI) values, the encapsulation type, and the dial-pool 
member. 
						

							  
4-12
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring DHCP Server Import
Step 3Create a dialer interface.
a.Enter configuration mode for the dialer interface.
b.Specify the MTU size as 1492.
c.Assign ip address negotiated to the dialer interface.
d.Configure the dialer group number. 
e.Configure PPP encapsulation and (if needed) Challenge Handshake Authentication Protocol 
(CHAP).
f.Configure IP negotiation of DNS and WINS requests.
Step 4Define an IP DHCP pool name.
a.Configure the network and domain name (if needed) for the DHCP pool.
b.Enter the import all command.
Step 5Configure a dialer list and a static route for the dialer interface.
Configuration Examples
The following example shows configuration of the DHCP server import on the Cisco router: 
router-820#show run
Building configuration...
Current configuration :1510 bytes
version 12.1
no service single-slot-reload-enable
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname router-820
logging rate-limit console 10 except errors
!
username 3620-4 password 0 lab
mmi polling-interval 60
mmi auto-configure
no mmi pvc
mmi snmp-timeout 180
ip subnet-zero
no ip finger
no ip domain-lookup
!
ip dhcp pool 2
import all
network 192.150.2.0 255.255.255.0
domain-name devtest.com
default-router 192.150.2.100 
lease 0 0 3
!
no ip dhcp-client network-discovery
vpdn enable
no vpdn logging
vpdn-group 1
request-dialin
protocol pppoe 
						

							  
4-13
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring DHCP Server Import
call rsvp-sync
!
interface Ethernet0
ip address 192.150.2.100 255.255.255.0
ip nat inside
!
interface ATM0
no ip address
no atm ilmi-keepalive
pvc 0/16 ilmi
!
pvc 1/40 
protocol pppoe
pppoe-client dial-pool-number 1
!
bundle-enable
dsl operating-mode auto
!
interface Dialer0
ip address negotiated
ip mtu 1492
ip nat outside
encapsulation ppp
dialer pool 1
dialer-group 1
ppp authentication chap
ppp ipcp dns request
ppp ipcp wins request
!
ip classless
ip route 0.0.0.0 0.0.0.0 Dialer0
no ip http server
!
ip nat inside source list 101 interface Dialer0 overload
access-list 101 permit ip any any
dialer-list 1 protocol ip list 101
snmp-server manager
!
voice-port 1
voice-port 2
voice-port 3
voice-port 4
!
line con 0
transport input none
stopbits 1
line vty 0 4
scheduler max-task-time 5000
end
The following example shows DHCP proxy client configuration:
3620-4#show run
version 12.1
no service single-slot-reload-enable
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname 3620-4
logging rate-limit console 10 except errors
!
username 820-uut1 password 0 lab
username 820-uut4 password 0 lab 
						

							  
4-14
Cisco 826, 827, 828, 831, 836, and 837 and Cisco SOHO 76, 77, 78, 91, 96, and 97 Routers Software Configuration Guide
78-14565-03
Chapter 4      Advanced Router Configuration
Configuring DHCP Server Import
memory-size iomem 10
ip subnet-zero
!
no ip finger
!
ip address-pool dhcp-proxy-client
ip dhcp-server 192.150.1.101
vpdn enable
no vpdn logging
!
vpdn-group 1
accept-dialin
protocol pppoe
virtual-template 1
!
call rsvp-sync
cns event-service server
!
interface Ethernet0/0
ip address 192.150.1.100 255.255.255.0
half-duplex
!
interface Ethernet0/1
no ip address
shutdown
half-duplex
!
interface ATM1/0
no ip address
no atm scrambling cell-payload
no atm ilmi-keepalive
pvc 1/40 
encapsulation aal5snap
protocol pppoe
!
interface Virtual-Template1
ip address 2.2.2.1 255.255.255.0
ip mtu 1492
peer default ip address dhcp
ppp authentication chap
!
ip kerberos source-interface any
ip classless
ip route 0.0.0.0 0.0.0.0 Ethernet0/0
no ip http server
!
dialer-list 1 protocol ip permit
dial-peer cor custom
!
line con 0
exec-timeout 0 0
transport input none
line aux 0
line vty 0 4
login
end
The following example shows configuration on the remote DHCP server:
2500ref-4#show run
version 12.1
service timestamps debug uptime
service timestamps log uptime
no service password-encryption