Configuring T1 & E1 Interfaces

Wide Area Network (WAN) provide the mechanism for connecting remote site together and connecting your Local Area Network (LAN) to the internet through a connection to an ISP.There are a variety of physical transports, T1/E1 connections are common means of transport. T1 circuit are generally used in domestic application while E1 circuits are widely deployed internationally. E1/T1 circuits are relatively inexpensive investment because they allow remote sites to share corporate resources at other location and thus eliminate the need of redundant equipment at multiple locations.

Configuring E1/T1 WAN applications includes six steps.

1: Configuring the physical interface (Ethernet and WAN Interface)
2: Configuring the Layer-2 protocol(s)
3: Bind the physical and virtual (Layer-2) interface
4: Create access-lists and policies (Including NAT)
5: Apply the policies to interface
6: Configuring the routing information (Either static or Dynamic (RIP, OSFP etc))

Physical Interface Configurations (T1, E1 and Ethernet)

To enable the appropriate interface, first we have to configure from global configuration prompt. For example, enter the following command to activate the interface configuration mode for the first T1 interface on a T1 module inserted in slot 1:

Head_Office > enable
Head_Office # configure terminal
Head_Office (config) # interface t1 1/1
Head_Office (config-t1 1/1) #

All interface are disable by default and must be activated using the no shutdown command. Interfaces will not be able to pass data until this command is entered.


Configuring T1 Interface

There are four main settings to consider when configuring T1 network interface namely Line coding (Coding), framing formate (framing), active channel (tdm-group), and clock source (clock source) must be all configured to match the circuit supplied by your network provider. By default all secure Router T1 interfaces are configured for ESF (framing esf), B8ZS (coding b8zs) and to recover clocking from the network circuit (clock source line). Generally the line coding, framing format, and clock source default values will be the correct ones for your application and should not be changed.
Each configured T1 interface must have the active channels specified using the tdm-group command because there are no default TDM groups defined. The active channels are entered as a single number representing 1 of the 24 T1 channel timeslots or as a contiguous group of channels. Following are the commands used for T1 configuration:

Head_Office # configure terminal
Head_Office (config) # interface t1 1/1
Head_Office (config-t1 1/1) #tdm-group 1 timeslots 1-24
Head_Office (config-t1 1/1) # no shutdown
Head_Office (config-t1 1/1) # exit

Configuring E1 Interfaces

There are four main settings to consider when configuring E1 network interface namely Line coding (Coding), framing formate (framing), active channel (tdm-group), and clock source (clock source) must be all configured to match the circuit supplied by your network provider. By default all secure Router E1 interfaces are configured for standard multi-frame without the optional CRC4 error correction (no framing crc4), and to recover clocking from the network circuit (clock source line). Generally the line coding, framing format, and clock source default values will be the correct ones for your application and should not be changed.

Each configured E1 interface must have the active channels specified using the tdm-group command because there are no default TDM groups defined. The active channels are entered as a single number representing 1 of the 31 E1 channel timeslots or as a contiguous group of channels. Following are the commands used for T1 configuration:

Head_Office # configure terminal
Head_Office (config) # interface e1 1/1
Head_Office (config-t1 1/1) #tdm-group 1 timeslots 1-31
Head_Office (config-t1 1/1) # no shutdown
Head_Office (config-t1 1/1) # exit

Configuring Ethernet Interfaces

Standard Ethernet configurations generally contains an IP address, a speed and duplex settings. By default, all secure Router Ethernet interfaces are configured to auto-detect the speed (as 10 or 100 Mbps) and are set to full-duplex. For most cases, these settings should suffice and will not be changed from the default state.
The following example commands configure an IP address of (10.10.x.x/24) and activates teh interface foe the eth 0/1 interface:

Head_Office (config) # interface eth 0/1
Head_Office (config-eth 0/1) # ip address 10.10.x.x 255.255.255.0
Head_Office (config-eth 0/1) # no shutdown
Head_Office (config-eth 0/1) # exit

Configuring Layer-2 Protocols (Frame-Relay, PPP, HDLC)

There are two main settings to consider when configuring Frame Relay interfaces. The interface type and signalling type must be configures to match the specification supplied on frame relay circuit by your network provider. Frame-relay interfaces have a sub-interfaces component for each PVC which must also be configured. Each frame-relay sub-interfaces contains a DLCI (Data Link Connection Identifier) and IP address because there are no default DLCI or IP address defined. Each PVC should also have a configured committed burst value (frame-relay bc) which is equivalent to the committed information rate (CIR) given to you by your network provider. PVC will also have a negotiated burst rate (frame-relay be) which is equivalent to the excess information rate (EIR) given to you by your network provider. Both CIR and EIR should be defined by you and your service provider at time of signing the service agreement.

NOTE: To know the appropriate EIR you should know the CIR and Physical bandwidth of both local and remote side. A general rule to the provision of burst value with the remote side CIR and configure the EIR with the difference between CIR and the actual physical bandwidth at the location. The committed burst value plus the EIR should not be greater than the physical bandwidth.

Head_Office (config) # interface fr 2.16
Head_Office (config-fr 2.16) # no shutdown
Head_Office (config-fr 2.16) # exit

Head_Office (config) # interface fr 2.16
Head_Office (config-fr 2.16) # frame-relay interface-dlci 16
Head_Office (config-fr 2.16) # frame-relay bc 768000
Head_Office (config-fr 2.16) # frame-relay be 768000
Head_Office (config-fr 2.16) # ip address 192.168.72.1/30
Head_Office (config-fr 2.16) # no shutdown
Head_Office (config-fr 2.16) # exit



Multilink Frame Relay Operation
Multilink Frame Relay operation increase bandwidth on your frame-relay service by aggregating multiple physical links into a single logical bundle. All the physical links in a multilink bundle are treated as a single entity by the system, allowing each PVC on he connection to dynamically share the total bandwidth of the bundle.
Physical links can be dynamically added and removed from the logical bundle, so a failure on one physical link does not halt the overall operation of the bundle. since all PVC have access to the entire bundle bandwidth, failure of a single physical connection in the bundle does not decrease the efficiency.

Multilink Frame Relay requires minimal configuration in your router, you first enable multilink operation on the frame relay interface (not sub-interface) and then bind the multiple physical interface to the single Frame Relay interface. For Example

Head_Office (config) # interface fr 1
Head_Office (config-fr 1) # frame-relay multilink
Head_Office (config-fr 1) # no shutdown

Now bind multiple physical interfaces tot he same multilink Frame Relay interface

Head_Office (config) # bind 1 t1 3/1 fr 1
Head_Office (config) # bind 2 t1 3/2 fr 1
Head_Office (config) # bind 3 t1 3/3 fr 1

Configuring PPP Interface

There are two settings to consider when configuring PPP interface, IP address and MTU. There are no IP address by default so we have to assign IP address and by default MTU is 1500 Bytes which works for many applications.

Head_Office (config) # interface ppp 1
Head_Office (config-ppp 1) # ip add 172.22.15.2/30
Head_Office (config-ppp 1) # no shutdown
Head_Office (config-ppp 1) # exit

Now for Multilink PPP Operation, first we have to enable this on the PPP interface and then bind the multiple physical interfaces tot he single PPP interface. Before configuration two things are kept in mind, PPP multilink fragmentation command at global configuration mode used for the fragmentation process which evenly divides the data among all the links in the bundle with a minimum packet size of 96 bytes and second command ppp multilink interleave command at global configuration mode used with streaming protocol to reduce delay by giving priority to packets identified as high priority. The command specify the configuration parameter required for multilink PPP interface:

Head_Office (config) # interface ppp 1
Head_Office (config-ppp 1) # interface ppp 1
Head_Office (config-ppp 1) # ppp multilink
Head_Office (config-ppp 1) # no shutdown

Now to bind multiple physical interface to the same multilink PPP interface:

Head_Office (config) # bind 1 t1 3/1 1 PPP 1
Head_Office (config) # bind 2 t1 3/2 2 PPP 1
Head_Office (config) # bind 3 t1 3/3 3 PPP 1

Binding Physical and Virtual Interface

Virtual interface must be bound to physical interface to create a WAN interface where Layer-2 signalling occurs. Use the bind command to connect the physical and virtual interfaces.

Following command listing depicts three bind to a multilink Frame Relay interface and a single bind to a PPP interface. Each bind has a unique label identifier (1 through 4)

Head_Office (config) # bind 1 t1 3/1 1 fr 1
Head_Office (config) # bind 2 t1 3/2 2 fr 1
Head_Office (config) # bind 3 t1 3/3 2 fr 1
Head_Office (config) # bind 4 t1 3/8 4 PPP 1

Now also define ACL and define routing of your own choice or as directed you to do so.

Hope it will be informative for you.

Thank You for reading!