Cisco MWR 1941-DC - 1941 Mobile Wireless Router User manual

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Cisco MWR 1941-DC Router with the
Cisco IOS IP-RAN Feature Set
FThe functionality of the MWR 1941-DC router is dependent on the Cisco IOS image running on it. This
document describes configuring the MWR 1941-DC router with the Cisco IOS IP-RAN feature set
(software image).
For additional configuration topics, refer to the Cisco IOS configuration guide and command reference
publications. These publications are available on the Documentation CD-ROM that came with your
router, on the World Wide Web from Cisco’s home page, or you can order printed copies separately.
This document contains the following sections:
•Feature Overview, page 2
•Configuring Tasks, page 8
•Monitoring and Maintaining the MWR 1941-DC Router, page 37
•Enabling Remote Management of the MWR 1941-DC Router, page 38
•Related Documentation, page 39

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Feature Overview
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Feature Overview
In an IP RAN application, the Cisco MWR 1941-DC router extends IP connectivity to the cell site and
Base Transceiver Station (BTS).
Through a FastEthernet interface to the BTS, the MWR 1941-DC router provides bandwidth-efficient IP
transport of voice and data bearer traffic, as well as maintenance, control, and signalling traffic, over the
leased line backhaul network between the BTS and leased line termination and aggregation node via
compression (cRTP/cUDP) and packet multiplexing (PPPmux and MLPPP).
Figure 1 shows the placement of and connections for the MWR 1941-DC router implemented in an
IP-RAN.
Figure 1 MWR 1941-DC Router in an IP-RAN Solution
In the IP-RAN, the BTS site consists of a pair of MWR 1941-DC routers. The pair of MWR 1941-DC
routers provides for an active and standby router for redundancy. A failure of the active MWR 1941-DC
router causes the standby router to take over as the active router for the BTS site.
Each pair of MWR 1941-DC routers at the BTS site is identical in hardware configuration. They connect
to each other through the BTS via the Fast Ethernet interfaces. The individual backhaul links to an
MWR 1941-DC router are cabled from a single T1/E1 termination block in the BTS, connecting to both
the active and standby routers utilizing a “Y” cable. The redundancy design to control the active/standby
transitions of the router pair leverages HSRP to control the relays on the VWIC-2MFT-T1-DIR (or
VWIC-2MFT-E1-DIR) in each router to ensure that the relays on the active router are closed and the
relays on the standby router are open to avoid double termination of the T1 (or E1).
Software Features with the Cisco IOS IP-RAN Feature Set
The software required for implementing the MWR 1941-DC router in an IP-RAN consists of two
components: Cisco IOS software running on the MIPs-based route processor portion of the
MWR 1941-DC router hardware, and microcode running on the Cisco network processor, also known as
“Parallel eXpress Forwarding (PXF).” When deployed in an IP-RAN, the MWR 1941-DC router is
customized for performance, high availability, quality of service, and link efficiency.
Cisco IOS software functions added to the MWR 1941-DC router IP-RAN feature set include:
•Redundancy logic—For monitoring Hot Standby Routing Protocol (HSRP) information to
determine the active and standby router and control T1 termination.
•Failover logic—To force a switchover for hardware failures or an over-temperature condition.
•Relay control—To open and close the T1/E1 interfaces on the active and standby routers.
•Diagnostic functions—To monitor the “health” of the standby MWR 1941-DC router.
Active
pBTS
MWR 1900 IP BTS router pair
100BaseT
T1/E1 backhaul link to
IP RAN aggregation node
Standby
65827

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Feature Overview
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This section contains the following information:
•MIPs-Based Software Features, page 3
•Network Processor (PXF) Software Features, page 3
•Redundancy Support, page 5
MIPs-Based Software Features
Standard Cisco IOS software features supported in the MWR 1914-DC IP-RAN feature set include:
•IP Fragmentation
•IP Multicast
•IGMP
•MLP, PPP Control Path (IPCP, NCP, LCP, CLNS)
•ACFC and PFC Handling During PPP Negotiation
•HSRP
•OSPF
•DHCP
•CDP
•NTP
•SNMP
Network Processor (PXF) Software Features
To achieve the required efficiency, when implemented in an IP-RAN, the MWR 1941-DC router
additionally has microcode running on the network processor to offload the fast-path processing of
packets. This allows the MWR 1941-DC router to support the traffic of up to 4 T1s or E1s (up to 60,000
packets per second) at a targeted 80% processor utilization while performing UDP/RTP header
compression/decompression (cUDP/cRTP) and PPPmux.
The following features are supported in the network processor:
•MAC Classify
•ICMP
•FIB (CEF)
•Load-balancing
•MAC Rewrite
•QoS Matching, including IP Access Lists (Input/Output Security ACLs are not supported), QoS
Group, IP Precedence, IP DSCP, and Input Interface
•QoS Actions, including Set IP Precedence, Set IP DSCP, Set QoS Group, Traffic Shaping, Class
Based WFQ (CB-WFQ), and Low Latency Queuing (LLQ)
•Maintenance of statistics, such as Forwarding, Drop, and Interface
•IPv4
•MLPPP, MLP, PPP Data Path (MLP LFI is not supported)
•PPPmux

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•cRTP/cUDP
•Link Noise Monitoring (LNM) provides configuration monitoring of individual T1/E1 circuit
quality
PPP Multiplexing/Demultiplexing
Encapsulated PPP frames contain several bytes of header information, which adds overhead to a network
that is used to transport PPP frames.
RFC 3153 describes a way to overcome this overhead. On the sending end, a multiplexor concatenates
multiple PPP frames (subframes) into a single, multiplexed frame (superframe). One header is included
in the superframe and the individual PPP subframes are separated by delimiters. On the receiving end, a
demultiplexor uses the delimiters to separate the individual PPP subframes.
The MWR 1914-DC router network processor software conforms to this specification and acts as both a
multiplexor and a demultiplexor.
RTP/UDP Header Compression
RTP is a protocol used for carrying packetized audio and video traffic over an IP network. RTP, described
in RFC 1889, is not intended for data traffic, which uses TCP or UDP. Instead, RTP provides end-to-end
network transport functions intended for applications with real-time requirements (such as audio, video,
or simulation data) over multicast or unicast network services.
In an RTP frame, there is a minimum 12 bytes of the RTP header, combined with 20 bytes of IP header,
and 8 bytes of UDP header. This creates a 40-byte IP/UDP/RTP header. By comparison, the RTP packet
has a payload of approximately 20 to 160 bytes for audio applications that use compressed payloads.
Given this ratio, it is very inefficient to transmit the IP/UDP/RTP header without compressing it.
Figure 2 RTP Header Compression
Before RTP header compression:
20 bytes 8 bytes
20 to 160 bytes
12 bytes
IP
Header
UDP RTP Payload
After RTP header compression:
2 to 4 bytes
20 to 160 bytes
IP/UDP/RTP header
Payload
12076

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Feature Overview
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RFCs 2508 and 2509 describe a method for compressing not only the RTP header, but also the associated
UDP and IP headers. Using this method, the 40 bytes of header information is compressed into
approximately 2 to 4 bytes, as shown in Figure 2. Because the frames are compressed on a link-by-link
basis, the delay and loss rate are lower, resulting in improved performance.
The MWR 1914-DC router network processor offloads both the compression and decompression of RTP
frames from the Cisco IOS software.
Note The MWR 1941-DC router can be configured to perform only IP/UDP compression, in which case the
header is reduced from 28 bytes to 2 to 4 bytes.
Redundancy Support
In an IP-RAN application, to ensure availability, the backhaul links to an MWR 1941-DC router are
redundantly cabled to the VWIC-2MFT-T1-DIR/ VWIC-2MFT-E1-DIR cards. This card, designed
specifically for the MWR 1941-DC router, is a modified 2-port T1/E1 Multiflex VWIC with Drop and
Insert.The modifications include the addition of relays to activate the T1/E1 ports. The relays allow “Y”
cabling for router redundancy where the T1/E1 link is not redundant and default to open. The relays are
controlled by HSRP/redundancy protocol between the two routers connected to the same T1/E1.
Note If you choose to use the MWR 1941-DC router in a non-redundant configuration, you must close the
relays on the card using the standalone subcommand. Also, redundancy parameters are processed when
the router is booted up. These parameters cannot be changed “on the fly.”
HSRP
Cisco’s Hot Standby Router Protocol (HSRP) is used to control which router is active and which is
standby. HSRP uses a priority scheme to determine which HSRP-configured router is to be the default
active router. Priority is determined first by the configured priority value, and then by the IP address. In
each case a higher value is of greater priority.
Supported MIBs
•CISCO-ACCESS-ENVMON-MIB
•CISCO-CDP-MIB
•CISCO-CLASS-BASED-QOS-MIB
•CISCO-CONFIG-COPY-MIB
•CISCO-CONFIG-MAN-MIB
•CISCO-ENVMON-MIB
•CISCO-FLASH-MIB
•CISCO-HSRP-EXT-MIB
•CISCO-HSRP-MIB
•CISCO-ICSUDSU-MIB
•CISCO-IMAGE-MIB
•CISCO-IP-STAT-MIB

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•CISCO-IPMROUTE-MIB
•CISCO-MEMORY-POOL-MIB
•CISCO-MOBILE-IP-MIB
•CISCO-PROCESS-MIB
•CISCO-QUEUE-MIB
•CISCO-SYSLOG-MIB
•CISCO-TCP-MIB
•ENTITY-MIB
•IF-MIB
•IGMP-MIB
•IPMROUTE-MIB
•OLD-CISCO-CHASSIS-MIB
•OLD-CISCO-FLASH-MIB
•OLD-CISCO-INTERFACES-MIB
•OLD-CISCO-IP-MIB
•OLD-CISCO-SYSTEM-MIB
•OLD-CISCO-TS-MIB
•RFC1213-MIB
•RFC1253-MIB
•RFC1406-MIB
•TCP-MIB
•UDP-MIB
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules,
go to the Cisco MIB website on Cisco.com at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
Note The MWR 1914-DC router uses the same software base as the Cisco 10000. As such, it shares the same
QoS MIB limitations of the Cisco 10000. For information about the Cisco10000 MIB support, see the
Cisco 10000 Series ESR MIB Specifications Guide on CCO at
http://www.cisco.com/univercd/cc/td/doc/product/aggr/10000/10kmibs/specgdll/index.htm.

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Limitations and Restrictions
Caution The Cisco MWR 1941-DC router does not support online insertion and removal (OIR) of WAN interface
cards. Any attempt to perform OIR on a card in a powered up router might cause damage to the card.
Caution Removing the compact flash from the Cisco MWR 1941-DC router during a read/write operation might
corrupt the contents of the compact flash, rendering it useless. To recover from an accidental removal of
or corruption to the compact flash, a maintenance spare with the appropriate bootable Cisco IOS
software image might be needed.
The following list of restrictions applies when implementing the MWR 1941-DC router in an IP-RAN.
Cisco IOS Software Features not Supported on the MWR 1941-DC Router
The Cisco MWR 1941-DC router requires a special version of Cisco IOS software. Not all Cisco IOS
software features can be used with the Cisco MWR 1941-DC router as the core routing is handled by the
network processor. A list of supported features is included in the “Software Features with the Cisco IOS
IP-RAN Feature Set” section on page 2. The following standard Cisco IOS software features are not
supported on the Cisco MWR 1941-DC router:
•Security Access Control Lists
•MPLS
•802.1Q VLANs
•Frame Relay (FR)
•MLP LFI
•ATM
•Use of additional WICs. The only supported WIC is the VWIC-2MFT-T1DIR/VWIC-2MFT-E1DIR.
(IP-RAN implementation only.)
Upgrading the VWIC-2MFT-T1-DIR Microcode
When upgrading the image on your Cisco MWR 1941-DC router, power cycle the router or perform a
microcode reload on the VWIC-2MFT-T1-DIR to ensure that the firmware for the VWIC-2MFT-T1-DIR
is updated during the upgrade.
Disabling PPP Multiplexing
To fully disable PPP multiplexing (PPPMux), issue the no ppp mux command on the T1 interfaces of
the routers at both ends of the T1 link. If PPP multiplexing remains configured on one side of the link,
that side will offer to receive PPP multiplexed packets.

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MLP LFI Support
MLP LFI is not supported by the Cisco MWR 1941-DC router. Therefore, MLP LFI must be disabled on
peer devices connecting to the Cisco MWR 1941-DC router T1 MLP connections.
ACFC and PFC Support on PPP Interfaces
If upgrading to Cisco IOS Release 12.2(8)MC2c or later for the ACFC and PFC support on PPP
interfaces, ensure that you upgrade the MGX-RPM-1FE-CP back card image first. After doing so,
immediately upgrade all MWR 1941-DC routers connected to the MGX-RPM-1FE-CP back card.
Configuring Tasks
See the following sections for configuration tasks for configuring the Cisco MWR 1941-DC router in an
IP-RAN.
•Before You Begin, page 8
•Slot and Port Numbering, page 9
•Verifying the Version of Cisco IOS Software, page 9
•Configuring the Host Name and Password, page 10
•Configuring Loopback Interfaces, page 11
•Configuring Fast Ethernet Interfaces, page 12
•Configuring Multilink Interfaces, page 17
•Configuring T1 and E1 Interfaces, page 23
•Configuring QoS Attributes, page 25
•Configuring Redundancy, page 28
•Configuring the Link Noise Monitor, page 30
•Saving the Configuration, page 33
•Verifying the Configuration, page 33
Before You Begin
Before you configure the MWR 1941-DC in an IP-RAN, please be aware of the following:
•Cisco IOS Release 12.2(8)MC2 or later “mwr1900-i-mz” image must be installed on the Cisco
MWR 1941-DC router.
•You cannot disable Cisco Express Forwarding (CEF) on the MWR 1941-DC. Commands such as
no ip cef will display an error message “%Cannot disable CEF on this platform.” Some commands,
such as no ip route-cache cef, will not return an error message. However, CEF will not be disabled
regardless of whether an error message is displayed.
•If you are using the MWR 1941-DC in a redundant configuration and are attaching the
MWR 1941-DC to a device that uses spanning tree, configure portfast on the device to avoid
problems with HSRP at start up.
•In case of a tie in priority, HSRP uses the IP address to determine the active router. Therefore, you
should ensure that the order of the IP addresses of the E1/T1 interfaces of the active router
corresponds to the order of the IP addresses of the E1/T1 interfaces of the standby router.

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Slot and Port Numbering
The Cisco MWR 1941-DC router chassis contains the following LAN and WAN interface types:
•Two built-in Fast Ethernet LAN interfaces
•Three slots in which you can install Voice/WAN interface cards (VWICs)
•One slot in which you can install a network module
The slot numbers are as follows:
•0 for all built-in interfaces
•0 for all built-in VWIC slots
•1 for the network module slot
The numbering format is:
Interface type Slot number/Interface number
Interface (port) numbers begin at 0 for each interface type, and continue from right to left.
•The two built-in Ethernet 10/100 interfaces are Fast Ethernet 0/0 and Fast Ethernet 0/1.
•The slot number for all VWIC interfaces in the built-in VWIC slot is always 0. (The W0, W1, and
W2 slot designations are for physical slot identification only.) Interfaces in the VWICs are
numbered from right to left, starting with 0/0 for each interface type, regardless of the physical
VWIC slot in which the VWICs are installed.
For example, if you have a VWIC in two of the VWIC slots (W0 and W1), then the interfaces are:
– Serial 0/0 and Serial 0/1 in physical slot W0
– Serial 0/2 and Serial 0/3 in physical slot W1
However, if you install a VWIC in physical slot W1 (leaving slot W0 empty), the interfaces in slot
W1 are Serial 0/0 and Serial 0/1. If you then add a VWIC to slot W0, the interface numbering will
shift. The configuration that you created for interfaces Serial 0/0 and Serial 0/1 will now be applied
to the VWIC in slot W0 and you will need to create a new configuration for the interfaces that you
previously configured on W1 (which will now be Serial 0/2 and Serial 0/3).
•The slot number of WIC/VWIC interfaces installed in slot 1 using a WAN network module is always
1 and the interfaces are always numbered from the right to left.
•The slot number for all network module interfaces is always 1 and the interfaces are always
numbered from right to left starting with 1/0.
Verifying the Version of Cisco IOS Software
To implement the MWR 1941-DC router in an IP-RAN, Cisco IOS Release 12.2(8)MC2 or a later must
be installed on the router. To verify the version of Cisco IOS software, use the show version command.
The show version command displays the configuration of the system hardware, the software version, the
names and sources of configuration files, and the boot images.

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Configuring the Host Name and Password
One of the first configuration tasks you might want to do is configure the host name and set an encrypted
password. Configuring a host name allows you to distinguish multiple Cisco routers from each other.
Setting an encrypted password allows you to prevent unauthorized configuration changes.
Command Purpose
Step 1 Router> enable
Password: password
Router#
Enter enable mode. Enter the password.
You have entered enable mode when the prompt
changes to Router#.
Step 2 Router# configure terminal
Enter configuration commands, one per line.
End with CNTL/Z.
Router(config)#
Enter global configuration mode. You have
entered global configuration mode when the
prompt changes to Router(config)#.
Step 3 Router(config)# hostname Router
Router(config)#
Change the name of the router to a meaningful
name. Substitute your host name for Router.
Step 4 Router(config)# enable secret guessme Enter an enable secret password. This password
provides access to privileged EXEC mode. When
a user types enable at the EXEC prompt
(Router>), they must enter the enable secret
password to gain access to configuration mode.
Substitute your enable secret for guessme.
Step 5 Router(config)# line con 0
Router(config-line)# exec-timeout 0 0
Router(config-line)# exit
Router(config)#
Enter line configuration mode to configure the
console port. When you enter line configuration
mode, the prompt changes to
Router(config-line)#.
Prevent the router’s EXEC facility from timing out
if you do not type any information on the console
screen for an extended period.
Exit back to global configuration mode.

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To verify that you configured the correct host name and password:
Step 1 Enter the show config command:
Router(config)# show config
Using 1888 out of 126968 bytes
!
version XX.X
.
.
.
!
hostname Router
!
enable secret 5 $1$60L4$X2JYOwoDc0.kqa1loO/w8/
.
.
.
Check the host name and encrypted password displayed near the top of the command output.
Step 2 Exit global configuration mode and attempt to re-enter it using the new enable password:
Router# exit
.
.
.
Router con0 is now available
Press RETURN to get started.
Router> enable
Password: guessme
Router#
Configuring Loopback Interfaces
The loopback interface is a software-only, virtual interface that emulates an interface that is always up.
The interface-number is the number of the loopback interface that you want to create or configure. There
is no limit on the number of loopback interfaces you can create.
The multilink interface is a virtual interface, if you are not going to assign an explicit IP address to the
interface, you should create a loopback interface for the multilink interface to enable IP processing on
the interface.
In the case where the MWR 1941-DC is used in a redundant configuration, you must also configure
loopback interfaces for the health and revertive interfaces. The health interface monitors the status of the
redundant configuration so that the standby router can take over if there is a problem with the active
router. The revertive interface is required to ensure that the switchover takes place. We recommend that
you use 101 for the health interface and 102 for the revertive interface.

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To configure a loopback interface, use the following commands, beginning in global configuration
mode:
Configuring Fast Ethernet Interfaces
To configure the FE interface of the MWR 1941-DC, complete the following tasks:
•Configuring the FE Interface IP Address
•Setting the Speed and Duplex Mode
•Configuring Routing Protocol Attributes
•Configuring PIM
•Configuring HSRP Support
•Enabling the FE Interface
Configuring the FE Interface IP Address
To configure the FE interface, use the following commands, beginning in global configuration mode:
Command Purpose
Step 1 Router(config)# interface loopback number Creates a loopback interface for the multilink
interface.
Note For the health and revertive interfaces, you do
not need to assign an IP address.
Step 2 Router(config-if)# ip address ip-address subnet-mask Assigns an IP address and subnet mask to the
interface.
Step 3 Router(config-if)# exit Exits interface configuration mode.
Command Purpose
Step 1 Router(config)# interface fastethernet slot/port Specifies the port adapter type and the location of the
interface to be configured.
The slot is always 0 and the port is the number of the
port (0 or 1).
Step 2 Router(config-if)# ip address ip-address subnet-mask Assigns an IP address and subnet mask to the
interface.
Step 3 Router(config-if)# exit Exits interface configuration mode.

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Setting the Speed and Duplex Mode
The Fast Ethernet ports of the MWR 1941-DC can run in full or half duplex mode and at 100 Mbps or
10 Mbps. The MWR 1941-DC also has an auto-negotiation feature that allows the router to negotiate the
speed and duplex mode with the corresponding interface on the other end of the connection.
Auto negotiation is the default setting for the speed and transmission mode.
When configuring an interface speed and duplex mode, note these guidelines:
•If both ends of the line support auto negotiation, we highly recommend the default auto negotiation
settings.
•When the auto negotiation is turned on for either speed or duplex, it auto negotiates both speed and
duplex.
•If one interface supports auto negotiation and the other end does not, configure duplex and speed on
both interfaces; do not use the auto setting on the supported side or the duplex setting will be half.
To configure the speed and duplex operation, use the following commands while in interface
configuration mode:
Configuring Routing Protocol Attributes
When used in the CDMA IP-RAN solution, the MWR 1941-DC must be configured to support the OSPF
routing protocol.
To configure OSPF routing protocol attributes, use the following commands while in interface
configuration mode:
Command Purpose
Step 1 Router(config-if)# duplex [auto | half |full]Specifies the duplex operation.
Step 2 Router(config-if)# speed [auto | 100 |10]Specifies the speed.
Command Purpose
Step 1 Router(config-if)# ip ospf message-digest-key key-id
md5 key
Enables OSPF Message Digest 5 (MD5)
authentication.
Step 2 Router(config-if)# ip ospf hello-interval seconds Configures the interval between hello packets that the
Cisco IOS software sends on the interface.
Step 3 Router(config-if)# ip ospf dead-interval seconds Configures the interval at which hello packets must
not be seen before neighbors declare the router down.

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Configuring PIM
Because the MWR 1941-DC is used in a multicast PPP environment, you should configure the Protocol
Independent Multicast (PIM) mode of the FE interface.
To configure the PIM mode, use the following command while in interface configuration mode:
Configuring HSRP Support
In redundant configurations, the MWR 1941-DC uses Cisco IOS Hot Switch Routing Protocol (HSRP)
to control the active and standby routers. To use HSRP, you must configure the standby priority attributes
and the IP address of the virtual router. Priority is determined first by the configured priority value, and
then by the IP address. In each case a higher value is of greater priority.
Note If you do not plan to use the MWR 1941-DC in a redundant configuration, do not configure HSRP
support and see Configuring Redundancy, page 28 for information about using the router in a standalone
environment.
Command Purpose
Router(config-if)# ip pim {sparse-mode | sparse-dense-mode |
dense-mode [proxy-register {list access-list | route-map
map-name}]}
Configures PIM on an interface, where:
•sparse-mode—Enables sparse mode of
operation.
•sparse-dense-mode—Treats the interface in
either sparse mode or dense mode of operation,
depending on which mode the multicast group
operates in.
•dense-mode—Enables dense mode of
operation.
•proxy-register—(Optional) Enables proxy
registering on the interface of a designated
router (DR) (leading toward the bordering
dense mode region) for multicast traffic from
sources not connected to the DR.
•list access-list—(Optional) Defines the
extended access list number or name.
•route-map map-name—(Optional) Defines
the route map.

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To configure HRSP, use the following commands while in interface configuration mode:
Command Purpose
Step 1 Router(config-if)# standby group name group-name Specifies the name of the standby group.
Note The standby group names must be “one” and
“two.” For FE 0/0, the command must be
standby 1 name one. For FE 0/1, the
command must be standby 2 name two.
Tip If you omit the group-name or if you enter a
group name that doesn’t begin with one or
two, the configuration will fail and there will
be a mismatch in the information displayed
by the show redundancy and show standby
commands.
Step 2 Router(config-if)# standby group ip address Enables HSRP and assigns an IP address to the
virtual router. This address is the same for both the
active and standby routers.
Step 3 Router(config-if)# standby group timers [msec]
hellotime [msec]holdtime
Configures the time between hello packets and the
time before other routers declare the active Hot
Standby or standby router to be down.
Note You must use 1 for the hello time and 3 for
the hold time.
Step 4 Router(config-if)# standby group preempt Indicates that the router can become the active router
when its priority is higher than all other
HSRP-configured routers. Without preemption, a
standby router will only transition to the active state
if HSRP “hello messages” cease.
In the CDMA IP-RAN solution, there may be
situations in which you want a switchover to occur in
the absence of a router or FE failure, therefore,
preemption is required.

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Note If you are using the MWR 1941-DC in a redundant configuration, you must also set the keepalives under
the FE interface to 1.
Router(config-if)# keepalive 1
Enabling the FE Interface
Once you have configured the FE interface, you can enable it.
To enable the FE interface, use the following command while in interface configuration mode:
Step 5 Router(config-if)# standby group track multilink
number decrement-value
Router(config-if)# standby group track loopback
number decrement-value
Router(config-if)# standby group track fastethernet
number decrement-value
Specifies other interfaces on the router for the HSRP
process to monitor in order to alter the HSRP priority
for a given group.
When using the MWR 1941-DC router in the CDMA
IP-RAN solution, you must configure each FE
interface to track the multilink interface, the
loopback interfaces, and the other FE interface.
Note In redundant configurations, you should issue
standby track commands for both the health
interface (loopback101) and the revertive
interface (loopback102) as well as for the
backhaul interface (multilink1). The
decrement values must be as follows: 10 for
the multilink, FE, and health interfaces; 5 for
the revertive interface.
Step 6 Router(config-if)# standby group priority 100 Configures HSRP priority.
Note We recommend that you specify a priority
of 100.
Command Purpose
Command Purpose
Router(config-if)# no shutdown Enables the interface.

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Configuring Multilink Interfaces
To configure the multilink interfaces, complete the following tasks:
•Configuring Multilink PPP, page 17
•Configuring IP Address Assignment, page 18
•Configuring PPP Multiplexing, page 18
•Configuring RTP/UDP Compression, page 20
•Configuring the RTP/UDP Compression Flow Expiration Timeout Duration, page 21
•Configuring Routing Protocol Attributes, page 22
•Configuring PIM, page 22
Configuring Multilink PPP
As higher-speed services are deployed, Multilink-PPP (MLP) provides a standardized method for
spreading traffic across multiple WAN links, while providing multivendor interoperability and
load-balancing on both inbound and outbound traffic.
A Multilink interface is a special virtual interface which represents a multilink PPP bundle. The
multilink interface serves to coordinate the configuration of the bundled link, and presents a single object
for the aggregate links. However, the individual PPP links that are aggregated together, must also be
configured. Therefore, to enable Multilink PPP on multiple serial interfaces, you need to first set up the
multilink interface, and then configure each of the serial interfaces and add them to the same multilink
interface.
The MWR 1941-DC router can support up to 16 T1 interfaces through the multilink interface.
To set up the multilink interface, use the following commands, beginning in global configuration mode:
Command Purpose
Step 1 RPM(config)# interface multilink number Specifies the multilink interface to be configured.
Step 2 RPM(config-if)# ppp multilink Enables multilink PPP operation.
Step 3 RPM(config-if)# multilink-group group-number1
or
RPM(config-if)# ppp multilink group group-number2
1. Cisco IOS Release 12.2(15)MC2a or later.
2. Cisco IOS 12.3(11)T or later.
Specifies an identification number for the multilink
interface.
Step 4 RPM(config-if)# ip unnumbered loopback number Enables IP processing on the multilink interface
without assigning an explicit IP address to the
interface, where number is the number of the
loopback interface that you configured in
Configuring Multilink PPP.

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Configuring IP Address Assignment
A point-to-point interface must be able to provide a remote node with its IP address through the IP
Control Protocol (IPCP) address negotiation process. The IP address can be obtained from a variety of
sources. The address can be configured through the command line, entered with an EXEC-level
command, provided by TACACS+ or the Dynamic Host Configuration Protocol (DHCP), or from a
locally administered pool.
IP address pooling uses a pool of IP addresses from which an incoming interface can provide an IP
address to a remote node through IPCP address negotiation process. IP address pooling also enhances
configuration flexibility by allowing multiple types of pooling to be active simultaneously.
To configure IP address assignment, use the following command while in multilink interface
configuration mode:
Configuring PPP Multiplexing
To enable and control the multiplexing of PPP frames, use the following commands while in interface
configuration mode:
Command Purpose
RPM(config-if)# peer default ip address {ip-address | dhcp |
pool [pool-name]}
Specifies an IP address, an address from a specific
IP address pool, or an address from the Dynamic
Host Configuration Protocol (DHCP) mechanism
to be returned to a remote peer connecting to this
interface.
Command Purpose
Step 1 RPM(config-if)# ppp mux Enables PPP multiplexing.
Step 2 RPM(config-if)# ppp mux delay integer Sets the maximum time delay.
Step 3 RPM(config-if)# ppp mux subframe length integer Sets the maximum length of the subframe.
Step 4 RPM(config-if)# ppp mux frame integer Sets the maximum length of the superframe
Step 5 RPM(config-if)# ppp mux subframe count integer Sets the maximum number of subframes in a
superframe.
Step 6 RPM(config-if)# ppp mux pid integer Sets the default PPP protocol ID.

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Configuring ACFC and PFC Handling During PPP Negotiation
With Cisco IOS Release 12.2(15)MC1 and later, ACFC and PFC handling during PPP negotiation can
be configured. By default, ACFC/PFC handling is not enabled.
To configure ACFC handling during PPP negotiation, use the following commands while in multilink
interface configuration mode:
Command Purpose
Step 1 RPM(config-if)# ppp acfc remote {apply | reject |
ignore}
Configures how the router handles the ACFC option
in configuration requests received from a remote
peer, where:
•apply—ACFC options are accepted and ACFC
may be performed on frames sent to the remote
peer.
•reject—ACFC options are explicitly ignored.
•ignore—ACFC options are accepted, but ACFC
is not performed on frames sent to the remote
peer.
Step 2 RPM(config-if)# ppp acfc local {request | forbid}Configures how the router handles ACFC in its
outbound configuration requests, where:
•request—The ACFC option is included in
outbound configuration requests.
•forbid—The ACFC option is not sent in
outbound configuration requests, and requests
from a remote peer to add the ACFC option are
not accepted.

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To configure PFC handling during PPP negotiation, use the following commands while in multilink
interface configuration mode:
Configuring RTP/UDP Compression
Enabling RTP/UDP compression (cRTP/cUDP) on both ends of a low-bandwidth serial link can greatly
reduce the network overhead if there is a lot of RTP traffic on that slow link. This compression is
beneficial especially when the RTP payload size is small (for example, compressed audio payloads of
20-50 bytes).
Note Before you can enable RTP header compression, you must configure a serial line that uses PPP
encapsulation.
To configure RTP header compression when using Cisco IOS Release 12.2(15)MC2a or prior, use the
following commands while in multilink interface configuration mode:
Command Purpose
Step 1 RPM(config-if)# ppp pfc remote {apply | reject |
ignore}
Configures how the router handles the PFC option in
configuration requests received from a remote peer,
where:
•apply—PFC options are accepted and PFC may
be performed on frames sent to the remote peer.
•reject—PFC options are explicitly ignored.
•ignore—PFC options are accepted, but PFC is
not performed on frames sent to the remote peer.
Step 2 RPM(config-if)# ppp pfc local {request | forbid}Configures how the router handles PFC in its
outbound configuration requests, where:
•request—The PFC option is included in
outbound configuration requests.
•forbid—The PFC option is not sent in outbound
configuration requests, and requests from a
remote peer to add the PFC option are not
accepted.
Command Purpose
Step 1 RPM(config-if)# ip rtp header-compression Enables RTP header compression for serial
encapsulations.
Step 2 RPM(config-if)# ip rtp compression-connections
number
Configures the total number of RTP header
compression connections on an interface.
By default, a total of 16 RTP compression
connections on an interface is supported.