Checking Link Status on Cisco Routers

Contents

• Show Leased Line Status
  • sh int
• Show Frame Relay Status
  • sh int
  • sh frame pvc
• Cisco online help

Show Leased Line Status

The "sh int" command gives you statistics and information about the serial port the leased line is plugged into.

You can either just type "sh int", which will show you all the serial ports on the router, or you can give it a specific port/subinterface. This info is in the "port" field in the customer database.

Here's an example:

gw1-sf-tlg>sh int s0
Serial0 is up, line protocol is up
  Hardware is HD64570
  Description: xanaplex
  Internet address is 140.174.99.5, subnet mask is 255.255.255.252
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 180/255
  Encapsulation PPP, loopback not set, keepalive set (10 sec)
  lcp state = OPEN
  ncp ipcp state = OPEN   ncp osicp state = NOT NEGOTIATED
  ncp ipxcp state = NOT NEGOTIATED   ncp xnscp state = NOT NEGOTIATED
  ncp vinescp state = NOT NEGOTIATED   ncp deccp state = NOT NEGOTIATED
  ncp bridgecp state = NOT NEGOTIATED   ncp atalkcp state = NOT NEGOTIATED
  ncp lex state = NOT NEGOTIATED
  Last input 0:00:01, output 0:00:00, output hang never
  Last clearing of "show interface" counters never
  Output queue 0/40, 17684 drops; input queue 1/75, 1469 drops
  5 minute input rate 470000 bits/sec, 317 packets/sec
  5 minute output rate 1095000 bits/sec, 409 packets/sec
     187892398 packets input, 2457376442 bytes, 391 no buffer
     Received 1 broadcasts, 0 runts, 0 giants
     11298 input errors, 7298 CRC, 1113 frame, 104 overrun, 121 ignored, 4848 ab
ort
     185463805 packets output, 1680113594 bytes, 0 underruns
     0 output errors, 0 collisions, 29 interface resets, 0 restarts
     402 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

Basic Things to Check

1. Serial should say "up"
   If it doesn't, then there is a low-level problem in the link.... either the line itself has a problem, or one or both ends are not correctly connected, or else one end is badly misconfigured.
2. Line protocol should say "up"
   Line protocol is the higher-level interaction between the routers on both ends of the link. If the serial is up but the line protocol is down, somebody's misconfigured.

Taking a Closer Look

1. Checking error counts
   If there are input errors, CRC, frame, overrun, ignored or abort errors, this could be bad. The trick is to determine when the errors happened. 'Last clearing of "show interface" counters' tells you how long it's been since the counters were reset to zero (this requires root access). If you're unsure, record the numbers and check back later. If they are going up, the problems are current.
2. Checking the configuration
   You can double check the interface settings such as the IP address, subnet mask, etc. which should match the values in the database.
3. Checking line traffic
   "Load" tells you how much of the line capacity is being used -- maximum is 255. The 5 minute input and output rates also tell you how many bits are flowing through the line in either direction. If the load and input/output rates are close to the maximum, the customer may see slowness and packet loss.

Show Frame Relay Status

Basic Commands:

1. sh int: shows port status
   
2. sh frame pvc: shows PVC status
   

The port status tells you whether or not the customer router and the TLG router are communicating; the PVC status tells you whether or not the top-level frame relay protocol is up and running. These are two separate things.

sh int

All of the TLG frame-relay circuits are on Cisco routers. The frame relay circuit is a single T1 like a leased line except that it has multiple customers on it. It plugs into a single Cisco serial port (i.e. gw2-sf-tlg@s5).

Most of our frame relay customers are also assigned to virtual "subinterfaces" which are software-based (i.e gw2-sf-tlg@s5.1). Some of our older customers do not have subinterfaces; you can only check the interface for the entire frame relay circuit.

You can either just type "sh int", which will show you all the serial ports on the router, or you can give it a specific port/subinterface. This info is in the "port" field in the customer database.

Generally you only need to check the status of the customer's subinterface unless it seems like a bunch of frame relay customers are down. If the customer doesn't have a subinterface, or if multiple customers are down, check the status of the frame relay circuit as a whole (same as checking a leased line, above).

Here's what a subinterface looks like:

gw2-sf-tlg>sh int s5.1
Serial5.1 is up, line protocol is up
  Hardware is HD64570
  Description: sinodog
  Internet address is 140.174.128.5 255.255.255.252
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 6/255
  Encapsulation FRAME-RELAY IETF

This is just a simplified version of what the leased line port tells you.

1. Serial should say "up"
   If it doesn't, then there is a low-level problem in the link.... either the line itself has a problem, or one or both ends are not correctly connected, or else one end is badly misconfigured. This is an OUTAGE.
2. Line protocol should say "up"
   Line protocol is the higher-level interaction between the routers on both ends of the link. If the serial is up but the line protocol is down, somebody's misconfigured. This is an OUTAGE.

sh frame pvc

All frame relay customers have a PVC (Permanent Virtual Circuit). Checking the PVC status on the router is equivalent to checking a leased line customer's CSU/DSU.

You can either just type "sh frame pvc", which will show you all the PVCs on the router, or you can give it a specific PVC to check. This info is in the "ourdlci" field in the customer database.

gw2-sf-tlg> show frame pvc 16
PVC Statistics for interface Serial0 (Frame Relay DTE)

DLCI = 16, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0

  input pkts 923337        output pkts 777739       in bytes 102323589
  out bytes 143546957      dropped pkts 0           in FECN pkts 0
  in BECN pkts 0           out FECN pkts 0          out BECN pkts 0
  in DE pkts 0             out DE pkts 0
  pvc create time 2w3d  last time pvc status changed 9:55:00

PVC Statistics for interface Serial5 (Frame Relay DTE)

DLCI = 16, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial5.1

  input pkts 2339335       output pkts 3411242      in bytes 124946087
  out bytes 1526974010     dropped pkts 0           in FECN pkts 0
  in BECN pkts 0           out FECN pkts 0          out BECN pkts 0
  in DE pkts 0             out DE pkts 0
  pvc create time 2w3d  last time pvc status changed 17:45:58

If more than one PVC shows up with the same DLCI, that means there's more than one frame relay network on this router. Check the INTERFACE serial information to figure out which one is the one you're looking for. In this case, it's the second one.

PVC STATUS

• ACTIVE - normal status, all should be OK.
• INACTIVE - could mean that the customer has turned off their end. If they haven't, then just have the customer tell pacbell about it.
• DELETED - The PVC between TLGnet and the customer site has been deleted! Usually means Pacbell has messed things up. Possibly could mean the customer router is no longer sending LMI or is wedged, but has only been the cause a couple of times. Since PacBell moves slowly, the customer should double check their configuration and powercycle their equipment.

Other Things to Look For

• pvc status change
  If the status has changed recently, the link may be flapping.
• DLCI USAGE
  This should say "LOCAL". If it doesn't, there is no current customer on this PVC.

Cisco Online Help

Type a ? and you'll get a list of all possible commands. Type the first word of a command and ? (ie, "show ?") and it will give you additional information.