ck source Line t1 27 clock source Line t1 28 clock source Line Configuring DS3s Here, we have a DS3 connected to interface 2/0. This is a channelized DS3, SO the framing is set to M23. The clock source defaults to Line. Unlike with Tls, this should normally be left alone, as clocking is usually provided from the SONET net- work upstream. Notice that there is a clock statement for the DS3, and additional clock statements for each T1 within the DS3. Cisco only supports M23 and C-bit framing for channelized DS3s. When using M13 on telecom equipment, use M23 on your Cisco gear. Once the controllers have been configured, the serial T1s can be configured as if they were regular T1s. The serial interfaces are a combination of the physical interfaces and the T1 numbers in the DS3, followed by a colon and the channel group assigned in the controller configuration: interface Serial2/0/1:1 description T1 #1 ip address 10.220.110.1 255.255.255.252 interface Serial2/0/2:1 description T1 #2 ip address 10.220.120.1 255.255.255.252 interface Serial2/0/3:1 description T1 #3 ip address 10.220.130.1 255.255.255.252 interface Serial2/0/4:1 description T1 #4 ip address 10.220.140.1 255.255.255.252 You cannot create a serial interface larger than a T1 within a channel- ized DS3. If you need multimegabit speeds, you'll need to create multiple T1s, and either bundle them with Multilink-PPP, or load- balance them using CEF or a routing protocol. This router (a 7304) has both channelized and clear-channel interface cards. When you do a show version on a router like this, the output can be confusing because the number of serial interfaces includes the clear-channel DS3s and any T1s you've con- figured from your channelized DS3s. This router contains four channelized DS3s and four clear-channel DS3s. If a channelized DS3 is not configured at the controller level, it does not appear in the output of the show version command. Because we have four clear-channel DS3s, which are serial interfaces by default, and we've Chapter 21: DS3 configured 