Jaycee's Networking

February 11, 2009

Media Types

Filed under: Information, IOS — Tags: — Jaycee @ 9:58 am

Cisco supports a huge variety of different media types. There are over 50 different types of interface adapters available for the 7200 series routers alone.

A. “show interface”:

Router# show interfaces fastethernet 3/0

FastEthernet3/0 is up, line protocol is up
  Hardware is AmdFE, address is 00e0.f7a4.5130 (bia 00e0.f7a4.5130)
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  keepalive set (10 sec)
  Full-duplex, 100Mb/s, 100BaseTX/FX
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:05:30, output 00:00:00, output hang never
  Last clearing of "show interface" counters 1w5d
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue 0/1000/64/0 (size/max total/threshold/drops)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     312 packets input, 18370 bytes, 0 no buffer
     Received 216 broadcasts, 0 runts, 0 giants, 0 throttles
     3 input errors, 0 CRC, 0 frame, 0 overrun, 3 ignored, 0 abort
     0 input packets with dribble condition detected
     15490 packets output, 1555780 bytes, 0 underruns
     2 output errors, 0 collisions, 2 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     2 output buffer failures, 0 output buffers swapped out

FastEthernet3/0 is up, line protocol is up

1. interface/line protocol are up/up
2. interface/line protocol are up/down => Not seeing correct Layer 2 information
3. interface/line protocol are down/down => Not receiving the correct Layer 1 physical signaling
4. administratively down

Hardware is AmdFE, address is 00e0.f7a4.5130 (bia 00e0.f7a4.5130)

1. FastEthernet interface uses a FastEtherent ASIC made by AMD.

2. The default MAC address used is the BIA (Burned-In Address).

a. Sometimes a piece of legacy equipment expects to see a particular MAC address, or there might be an ACL that filters traffic based on this address. It can be awekward to deal with hardware problems that force you to replace or upgrade either a router or a module. You can use “mac-address” command to give this router the same address as the previous router.

b. If two devices wind up with the same MAC address, it can disrupt traffic for both devices as the switches try to figure out which one is which. If one of these devices is a router, it can disrupt all off-segment traffic. MAC addresses MUST be unique!

MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec
reliability 255/255, txload 1/255, rxload 1/255

1. 1500-byte MTU (Maximum Transmission Unit) size is typical for IP networks, you can change it by “mtu” command. Using a variety of different MTU values can cause performance problems due to fragmentation.

a. “mtu” command sets the Layer 2 MTU, which applies to all protocols.

b. “ip mtu” command only affects IP packets.

c. MTU will reset the interface. It’s better to issue a “shutdown” command before making this change.

2. BW shows the configured bandwidth of the interface, but it’s not the actual throughput of the interface. On serial interfaces, the router will usually show the default value here. It’s used for calculating routing protocol metrics and converting raw bit transmission rates into utilization statistics. DCE (Data Communications Equipment) serial interfaces supplies the clock signal that estimates the theoretical maximum throughput, and you can change it by “bandwidth” command.

3. reliability is no longer used.

4. txload represents the traffic utilizaion for the outbound interface; rxload represents the traffic utilization for the inbound interface. Both values are fractions of 255 which reprented using an 8-bit variable. txload and rxload values are rates that the router has to measure them by counting the number of bits send or received over a finite period of time. By default, the interval is 5 minutes. You can change it by “load-interval” command. The load data is used to compute load statistics, including input rate in bits and packets per second, output rate in bits and packets per second, load, and reliability.

Encapsulation ARPA, loopback not set
keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00

1. At Layer 2, it uses ARPA encapsulation. (The older ARPA encapsulation standard for IP packets is also called Ethernet II. IEEE standards standards differed from the existing ARPA standard. IP continues to use the old standard, while other Layer 3 protocols such as IPX offer a choice of encapsulation types.) The interface above is configured only for IP, thus it shows ARPA encapsulation.

2. Default keepalive value is 10 seconds. This interface send out a small packet every 10 sec to check if the interface is still working properly.

Last input 00:05:30, output 00:00:00, output hang never
Last clearing of “show interface” counters
1w5d

1. How long it’s been since the router has sent or received a packet on this itnerface

2. How long it’s been since last time cleared the statistical counters on this interface

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue 0/1000/64/0 (size/max total/threshold/drops)

1. size: the number of packets currently in each queue

2. max: the maximum number of packets that the queue can hold

5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec

312 packets input, 18370 bytes, 0 no buffer
Received 216 broadcasts, 0 runts, 0 giants, 0 throttles
3 input errors, 0 CRC, 0 frame, 0 overrun, 3 ignored, 0 abort
0 input packets with dribble condition detected
15490 packets output, 1555780 bytes, 0 underruns
2 output errors, 0 collisions, 2 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
2 output buffer failures, 0 output buffers swapped out

First two lines show the rates for both sending and receiving data through this itnerface, measured in both bits per second and packets per second that averaged over a 5 minute period.

The serial interface output ends with two more lines:

2 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up

1. The interface has gone up and down 2 times since the last time the counters were cleared.

2. Second line shows the current state of all of the serial signals.

3. DCE/DTE:

a. DCE (Data Communications Equipment) device raises a voltage on DCD (Data Carrier Detect) pin to indicate that the link is ready for transmitting data.

b. DCE send the DSR (Data Set Ready) signal when it’s ready to send or receive data.

c. When DTR (Data Terminal Ready) signal is high, it means that the DTE (Data Terminal Equipment) device is ready to send or receive data.

d. By default, DTE device will wait until it sees the DSR signal and the DCE device will wait for the DTR signal before sending any packets.

e. RTS (Request To Send) signal indicates that the DTE device would like to send data and is checking to make sure that the link and the far end are ready to receive it.

f. If everything is ready, the DCE device responds by raising the CTS (Clear To Send) signal.

g. Only DCE interfaces can supply the clock signal on synchronous serial connections. Use “clock rate” command on an interface implies this interface is the DCE device.

B. “show ip interface brief”:

Router# show ip interface brief
Interface     IP-Address     OK?  Method  Status                  Protocol
Ethernet0     10.108.00.5    YES  NVRAM   up                      up
Ethernet1     unassigned     YES  unset   administratively down   down
Loopback0     10.108.200.5   YES  NVRAM   up                      up
Serial0       10.108.100.5   YES  manual  up                      up

1. “OK?“: whether the router thinks that interface is operating correctly

2. “Method“: how the interface acquired its IP address. IP addresses of almost all of these interfaces were configured by NVRAM. It means that they haven’t changed since the last reboot. One of the interface was “manually” configured since the last reboot.

3. “NVRAM“: Configuration file in NVRAM

C. “show interface stats”:

Router# show interface fastethernet 0/3 stats 
Fastethernet0/3
          Switching path    Pkts In   Chars In   Pkts Out  Chars Out
               Processor    3459994 1770812197    4141096 1982257456
             Route cache   10372326 3693920448     439872  103743545
       Distributed cache   19257912 1286172104   86887377 1184358085
                   Total   33090232 2455937453   91468345 3270359086

1. “Processor“: shows both how many packets and how many characters the router has switched using process switching.

2. “Route cache“: shows the values for fast switching.

3. “Pkts In” and “Chars In“: show the values for incoming packets

4. “Pkts Out” and “Chars Out“: show values for packets transmitted out through this interface

D. For switching information for the interface:

Router#show interfaces FastEthernet0/1 switching

E. For details on the IP configuration of the interface:

Router#sh ip interface Fa0/1

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