Cisco Router Port Naming

Nerd Cafe

In Cisco networking, routers have different types of interfaces (ports) used for data transmission. Understanding Cisco router port naming is essential for configuring and troubleshooting networks.

Step 1: Understanding Cisco Router Interfaces

Cisco routers have multiple types of ports/interfaces, each serving a specific purpose. The common types include:

1. Ethernet Interfaces (FastEthernet, GigabitEthernet, TenGigabitEthernet)

2. Serial Interfaces (for WAN connections)

3. Management Interfaces (Console, AUX)

4. Loopback Interfaces (Virtual interfaces for testing)

Each of these interfaces follows a structured naming convention.

Step 2: Cisco Router Interface Naming Convention

The naming format for interfaces on a Cisco router is:

<InterfaceType> <Slot/Port>

Breaking it Down:

1. Interface Type: Specifies the technology used (e.g., FastEthernet, GigabitEthernet, Serial).

2. Slot: Represents the slot number where the module is inserted (in modular routers).

3. Port: Identifies the specific port number within the slot.

Step 3: Common Interface Types and Their Naming

1. Ethernet Interfaces

• Used for LAN connectivity.

• Named based on speed:

  • FastEthernet → 100 Mbps

  • GigabitEthernet → 1 Gbps

  • TenGigabitEthernet → 10 Gbps

Examples:

FastEthernet 0/0  → First FastEthernet port
GigabitEthernet 0/1 → First GigabitEthernet port
TenGigabitEthernet 1/0/1 → First 10G port on slot 1

Example in CLI:

Router# show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
FastEthernet0/0        192.168.1.1     YES manual up                    up
GigabitEthernet0/1     192.168.2.1     YES manual up                    up

2. Serial Interfaces (for WAN Connections)

• Used for point-to-point WAN links.

• Naming format: Serial <slot/port>.

Example:

Serial 0/1/0 → First serial port in slot 1

Example in CLI:

Router# show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
Serial0/1/0           10.0.0.1        YES manual up                    up

3. Management Interfaces

Cisco routers have two management ports:

• Console Port (Console 0) – Used for local access via a cable.

• Auxiliary Port (Aux 0) – Used for remote access via modem.

Example in CLI:

Router# show line
  0 con 0   // Console port
  1 aux 0   // Auxiliary port

4. Loopback Interfaces

• Virtual interfaces used for testing and router identification.

• Always up unless manually disabled.

• Naming: Loopback <ID>.

Router(config)# interface Loopback0
Router(config-if)# ip address 192.168.100.1 255.255.255.255

Step 4: Practical Configuration Examples

Let's configure different interfaces on a router.

Router#show ip interface brief 
Interface              IP-Address      OK? Method Status                Protocol
 
FastEthernet0/0        unassigned      YES unset  administratively down down
 
FastEthernet0/1        unassigned      YES unset  administratively down down
 
Serial0/0/0            unassigned      YES unset  administratively down down
 
Serial0/1/0            unassigned      YES unset  administratively down down
 
Serial0/1/1            unassigned      YES unset  administratively down down
 
Vlan1                  unassigned      YES unset  administratively down down
Router#

Example 1: Configuring an Ethernet Interface

Router#configure terminal 
Router(config)#interface fastEthernet 0/0
Router(config-if)#ip address 192.168.1.1 255.255.255.0
Router(config-if)#no shutdown 
Router(config-if)#exit
Router(config)#exit
Router#show ip interface brief 
Interface              IP-Address      OK? Method Status                Protocol
 
FastEthernet0/0        192.168.1.1     YES manual up                    down
 
FastEthernet0/1        unassigned      YES unset  administratively down down
 
Serial0/0/0            unassigned      YES unset  administratively down down
 
Serial0/1/0            unassigned      YES unset  administratively down down
 
Serial0/1/1            unassigned      YES unset  administratively down down
 
Vlan1                  unassigned      YES unset  administratively down down
Router#

Example 2: Configuring a Serial Interface

Router#configure terminal 
Router(config)#interface serial 0/0/0
Router(config-if)#ip address 10.0.0.1 255.255.255.252
Router(config-if)#clock rate 64000
Router(config-if)#no shutdown 
Router(config-if)#exit
Router(config)#exit
Router#show ip interface brief 
Interface              IP-Address      OK? Method Status                Protocol
 
FastEthernet0/0        192.168.1.1     YES manual up                    down
 
FastEthernet0/1        unassigned      YES unset  administratively down down
 
Serial0/0/0            10.0.0.1        YES manual down                  down
 
Serial0/1/0            unassigned      YES unset  administratively down down
 
Serial0/1/1            unassigned      YES unset  administratively down down
 
Vlan1                  unassigned      YES unset  administratively down down
Router#

Example 3: Configuring a Loopback Interface

Router#configure terminal 
Router(config)#interface loopback 0
Router(config-if)#ip address 192.168.10.1 255.255.255.255
Router(config-if)#exit
Router(config)#exit
Router#show ip interface brief 
Interface              IP-Address      OK? Method Status                Protocol
 
FastEthernet0/0        192.168.1.1     YES manual up                    down
 
FastEthernet0/1        unassigned      YES unset  administratively down down
 
Serial0/0/0            10.0.0.1        YES manual down                  down
 
Serial0/1/0            unassigned      YES unset  administratively down down
 
Serial0/1/1            unassigned      YES unset  administratively down down
 
Loopback0              192.168.10.1    YES manual up                    up
 
Vlan1                  unassigned      YES unset  administratively down down
Router#

Step 5: Troubleshooting Interface Issues

1. Checking Interface Status

Router#show ip interface brief 
Interface              IP-Address      OK? Method Status                Protocol
 
FastEthernet0/0        192.168.1.1     YES manual up                    down
 
FastEthernet0/1        unassigned      YES unset  administratively down down
 
Serial0/0/0            10.0.0.1        YES manual down                  down
 
Serial0/1/0            unassigned      YES unset  administratively down down
 
Serial0/1/1            unassigned      YES unset  administratively down down
 
Loopback0              192.168.10.1    YES manual up                    up
 
Vlan1                  unassigned      YES unset  administratively down down
Router#

• Up/Up → Interface is working.

• Up/Down → Layer 1 issue (cable, hardware failure).

• Admin Down → Interface is manually disabled (use no shutdown).

2. Checking Interface Details

Router#show interfaces serial 0/0/0
Serial0/0/0 is down, line protocol is down (disabled)
  Hardware is HD64570
  Internet address is 10.0.0.1/30
  MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, loopback not set, keepalive set (10 sec)
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0 (size/max/drops); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops)
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 96 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions
     DCD=down  DSR=down  DTR=down  RTS=down  CTS=down
Router#

3. Checking Cable and Hardware Issues

Router#show controllers serial 0/0/0
Interface Serial0/0/0
Hardware is PowerQUICC MPC860
No serial cable attached
idb at 0x81081AC4, driver data structure at 0x81084AC0
SCC Registers:
General [GSMR]=0x2:0x00000000, Protocol-specific [PSMR]=0x8
Events [SCCE]=0x0000, Mask [SCCM]=0x0000, Status [SCCS]=0x00
Transmit on Demand [TODR]=0x0, Data Sync [DSR]=0x7E7E
Interrupt Registers:
Config [CICR]=0x00367F80, Pending [CIPR]=0x0000C000
Mask   [CIMR]=0x00200000, In-srv  [CISR]=0x00000000
Command register [CR]=0x580
Port A [PADIR]=0x1030, [PAPAR]=0xFFFF
       [PAODR]=0x0010, [PADAT]=0xCBFF
Port B [PBDIR]=0x09C0F, [PBPAR]=0x0800E
       [PBODR]=0x00000, [PBDAT]=0x3FFFD
Port C [PCDIR]=0x00C, [PCPAR]=0x200
       [PCSO]=0xC20,  [PCDAT]=0xDF2, [PCINT]=0x00F
Receive Ring
        rmd(68012830): status 9000 length 60C address 3B6DAC4
        rmd(68012838): status B000 length 60C address 3B6D444
Transmit Ring
        tmd(680128B0): status 0 length 0 address 0
        tmd(680128B8): status 0 length 0 address 0
        tmd(680128C0): status 0 length 0 address 0
        tmd(680128C8): status 0 length 0 address 0
        tmd(680128D0): status 0 length 0 address 0
        tmd(680128D8): status 0 length 0 address 0
        tmd(680128E0): status 0 length 0 address 0
        tmd(680128E8): status 0 length 0 address 0
        tmd(680128F0): status 0 length 0 address 0
        tmd(680128F8): status 0 length 0 address 0
        tmd(68012900): status 0 length 0 address 0
        tmd(68012908): status 0 length 0 address 0
        tmd(68012910): status 0 length 0 address 0
        tmd(68012918): status 0 length 0 address 0
        tmd(68012920): status 0 length 0 address 0
        tmd(68012928): status 2000 length 0 address 0

tx_limited=1(2)
 
SCC GENERAL PARAMETER RAM (at 0x68013C00)
Rx BD Base [RBASE]=0x2830, Fn Code [RFCR]=0x18
Tx BD Base [TBASE]=0x28B0, Fn Code [TFCR]=0x18
Max Rx Buff Len [MRBLR]=1548
Rx State [RSTATE]=0x0, BD Ptr [RBPTR]=0x2830
Tx State [TSTATE]=0x4000, BD Ptr [TBPTR]=0x28B0
 
SCC HDLC PARAMETER RAM (at 0x68013C38)
CRC Preset [C_PRES]=0xFFFF, Mask [C_MASK]=0xF0B8
Errors: CRC [CRCEC]=0, Aborts [ABTSC]=0, Discards [DISFC]=0
Nonmatch Addr Cntr [NMARC]=0
Retry Count [RETRC]=0
Max Frame Length [MFLR]=1608
Rx Int Threshold [RFTHR]=0, Frame Cnt [RFCNT]=0
User-defined Address 0000/0000/0000/0000
User-defined Address Mask 0x0000


buffer size 1524

PowerQUICC SCC specific errors:
0 input aborts on receiving flag sequence
0 throttles, 0 enables
0 overruns
0 transmitter underruns
0 transmitter CTS losts
0 aborted short frames

Router#

Keywords

Cisco router ports, interface naming, FastEthernet, GigabitEthernet, TenGigabitEthernet, Serial interface, Loopback interface, Console port, AUX port, WAN interface, LAN interface, network configuration, IP addressing, show ip interface brief, no shutdown command, clock rate command, Cisco CLI, interface troubleshooting, router management, Packet Tracer, سیسکو