Serial Link Troubleshooting - Maipu

Today I was troubleshooting one case, Maipu router as CPE with last mile as Serial link.

 As we all know, serial interface configuration is not complicated.

Below is standard configuration for serial interface in Maipu routers.

interface serial0/0

 physical-layer sync

 encapsulation ppp

ip address  x.x.x.x 255.255.255.252

exit

As router is DTE device, no need to configure clock rate under serial interface.

Then also the line protocol was not coming up. After debugging the interface, I didn’t find any IPCP events.

After analysis of debugging logs we got to know, The peer router is  not sending IPCP packets to Maipu router.

So in show output we cannot see destination address, it is showing 0.0.0.0

serial0/0:

     line protocol is down

     Flags: (0x80f0) POINT-TO-POINT MULTICAST RUNNING

     Type: PPP

     Internet address: x.x.x.x/30

     Destination Internet address: 0.0.0.0

     Queue strategy: FIFO , Output queue: 0/16 (current/max packets)(0)

     Metric: 0, MTU: 1500, BW: 128 Kbps, DLY: 20000 usec, VRF: global

     Reliability 255/255, Txload 1/255, Rxload 1/255

     5 minutes input rate 0 bits/sec, 0 packets/sec

     5 minutes output rate 0 bits/sec, 0 packets/sec

     0 packets received; 41 packets sent

     0 multicast packets received

     0 multicast packets sent

     0 input errors; 0 output errors

     0 collisions; 0 dropped

      LCP:REQUEST SENT

      encap-type: simply PPP

rxFrames: 3, rxChars: 54

txFrames: 438, txChars: 5894

rxNoOctet: 39, rxAbtErrs: 1, rxCrcErrs: 13

rxOverrun: 0, rxLenErrs: 38015188, txUnderrun: 0

DCD=up  DSR=up  DTR=up  RTS=up  CTS=up  TxC=up

Rate = 2000000 bps

As you can see the last status in bold is up. That means majorly no problem from our end.

Below is description for status –

DCD: INPUT/OUTPUT, the carrier detection signal.

DSR: INPUT, the data service request signal, input by the peer DTR.

DTR: OUTPUT, the terminal device is ready; output the DSR to the peer Side.

RTS: OUTPUT, the sending signals of the request data; output the CTS to the peer side, used for the hard flow control.

CTS: INPUT, allows the data sending signals, input from the peer RTS, used for hard flow control.

TxC: INPUT, the data sending clock. In DTE mode, it is input from the outside ,in DCE mode, generated by itself.

After this output, I added one command to configure manual IPCP peer under serial interface. Then it started working.

Below is working configuration –

interface serial0/0

 physical-layer sync

 encapsulation ppp

ip address  10.1.1.1 255.255.255.252

peer default address  10.1.1.2

exit

In future you face any time such issue you can try this command in Maipu routers for serial troubleshooting.

Hope this post is informative for you.

For any feedback, Plz comment with your Name and Mail id. New users can use
Name/URL option.

Thanks for reading…

L2 QOS - 802.1p Priority

This section will explain you about 802.1p priority field in L2 header.This field is majorly used in L2 QOS. 

      The 802.1p priority is located in the L2 packet header. It is used when you don’t want to analyze the L3 packet header, but need to ensure QOS in L2 environment. As shown in below diagram, the 4-byte 802.1Q header contains 2-byte TPID (Tag Protocol Identifier valued as 0x8100) and 2-byte TCI (Tag Control Information).

Figure 1 - Ethernet Frame with 802.1Q Header

The following figure shows the detailed contents of the 802.1Q header. Ethernet frame with 802.1Q header.

Figure 2 802.1Q header

As shown in above diagram, the Priority field in TCI is the 802.1p priority. It comprises three bits and the value range is 0-7.

It is called 802.1p priority.

Hope this information is informative for you. In coming post, I will share 802.1p configuration for L2 QOS.

For any feedback, Plz comment with your name and mail ID. For new users, you can use Name/URL option. 

Thanks for reading...