Serial Interface Settings

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Sep 20th, 2005
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Serial2/0 is up, line protocol is up

Hardware is M4T


Internet address is

MTU 1500 bytes, BW 2048 Kbit, DLY

20000 usec,

reliability 255/255, txload 100/255, rxload 4/255

Encapsulation HDLC, crc 16, loopback not set

Keepalive set (10 sec)

Restart-Delay is 0 secs

Last input 00:00:04, output 00:00:00, output hang never

Last clearing of "show interface" counters 02:48:05

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 12

Queueing strategy: weighted fair

Output queue: 0/1000/64/12 (size/max total/threshold/drops)

Conversations 0/26/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 1536 kilobits/sec

5 minute input rate 34000 bits/sec, 50 packets/sec

5 minute output rate 811000 bits/sec, 455 packets/sec

508692 packets input, 33804450 bytes, 0 no buffer

Received 1009 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

3182148 packets output, 1705734195 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

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

Questions are:

MTU 1500 bytes--------------- Why MTU Size is 1500 bytes ?? Why can't 1000 or 2000 ?

DLY 20000 usec--------------- Why Delay is 20000 usec ?? Why not some other thing ?

reliability 255/255---------- What is 255/255 ? Why not 300/300 ??

Input queue: 0/75/0/0-------- Is this for input traffic from other router ?

Total output drops: 12------- What is this drop contains ?? If i want to be zero, what am i suppose to do ?

Output queue: 0/1000/64/12--- Is this for outbound traffic from this router ?

Conversations 0/26/256------ What is this ??

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Richard Burts Tue, 09/20/2005 - 05:08
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MTU value of 1500 is the default. I assume, though I do not know it for sure, that this value was chosen to provide compatibility with frames coming from Ethernet and this will reduce the possible need to fragment frames. Reducing fragmentation is a good thing on a router. There are config commands on the interface that give you the ability to adjust the MTU.

DLY of 20000 is the default value chosen. It is chosen to help scale the capacity of the serial interface relative to LAN interfaces. There is a configuration command on the interface where you can specify a different value if you choose to do so. The primary effect of changing the delay would be on the calculation of EIGRP routes. So if you use EIGRP as your routing protocol, changing the delay could change the routing decisions that EIGRP will make. If you have evaluated your network and decide that you want to change the delay, go ahead and do so. It might improve things, or it might make things worse if your analysis was faulty.

reliability of 255/255 indicates perfect reliability. the value of 255 was chosen because of the nature of binary numbers. 255 is the highest value you can achieve with an 8 bit number.

Input queue is the queue for inbound traffic. It would be frames from the router on the other end of the connection.

Output drops are frames that were dropped because the router could not send them quickly enough or did not have sufficient output buffers available. It happens some times when there is input from a fast LAN interface and output to a slow serial interface. If you want it to be zero slow down the input traffic.

Output queue is the queue for traffic outbound on this serial interface.

Conversations are exchanges of packets marked by the source and destination addresses and source and destination port numbers. This concept is used in Fair Queuing.



sriram_73 Wed, 09/21/2005 - 22:57
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Pls refer the attachment below for your ref:

In this diagram, from CITY-A -7th floor is trying to reach Local Network-Y (one of the unix server). Connections are getting established and worked fine till last week. Now we had connected Alteon FW in to Datacenter network.

After connecting to FW in the network, from CITY-A-7th Floor to Local Network-Y is giving problem. The problem is users are able to establish the telnet & http connections. After 4 Hrs seems to be slow and we need to restart the server again. Again Next 4 hrs same problem.

During this scnario, we observed that , Total output drops on the CITY-Z WAN Router is increasing from 0 to 100, on.. and the same time Alteon FW data flow is not happening. After restarting the server, it is working fine for 4 hrs again.

Qn is:

Do we need to increase the Buffer rating on Routers ? If so, can we enable the buffer rating for particular interface so that it will affect others??

If so, please let me know the procedures .

or please suggest me what could be the problem




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