Cisco Router 1900

Posted on 2013-09-03
Medium Priority
Last Modified: 2013-09-04
We have a Cisco Router 1900, and our ISP told us that our config (below) has the wrong duplex setting. They want us to change it to 100 FULL.

1. What is the command to change the duplex to FULL (without restarting the router).
2. What if the link goes down, how do I revert back to the old settings (AUTO)?

interface GigabitEthernet0/0
 description Internet via $ETH-WAN$$FW_OUTSIDE$
 ip address 209.xx.xx.xx
 ip access-group 101 in
 no ip redirects
 no ip proxy-arp
 ip verify unicast reverse-path
 ip flow ingress
 duplex auto
 speed 100
 no mop enabled
Question by:pzozulka
LVL 14

Accepted Solution

anoopkmr earned 1000 total points
ID: 39461305

interface GigabitEthernet0/0
spped 100
duplex full

sh int gi 0/0  will show the current settings .

Author Comment

ID: 39461428

GigabitEthernet0/0 is up, line protocol is up
  Hardware is CN Gigabit Ethernet, address is 0007.7dd1.xxxx
  Description: Internet via $ETH-WAN$$FW_OUTSIDE$
  Internet address is 209.xx.xx.xx/30
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 15/255, rxload 5/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Half-duplex, 100Mb/s, media type is RJ45

What about question #2 in the original post? What if the link goes down? Sorry I'm new to Cisco.

What would be the best way to revert back to old settings? I'm thinking just to restart the router, since it will revert back to the START config which doesn't preserve the command settings you recommended.

Is that a good option, or can you recommend better?
LVL 14

Assisted Solution

anoopkmr earned 1000 total points
ID: 39461446
show int --> shows half duplex.. did u apply the commands

regarding question number 2 ...  no need to restart .

just change the duplex to  auto ( duplex auto)

int gi 0/0
no shut.
Get your problem seen by more experts

Be seen. Boost your question’s priority for more expert views and faster solutions


Author Comment

ID: 39461491
I haven't applied any commands yet. I'm just showing that SHOW RUN says the duplex is AUTO, and SHOW INT GI 0/0 says the duplex is HALF. The ISP recommended to use FULL.
LVL 14

Expert Comment

ID: 39461578
i see..

that means other ( ISP) side is configured for  HALF duplex..  I dont know  for what reason they asked u to set full duplex..    if we go for manual settings then both side duplex and speed settings has to be same  otherwise  duplex mismatch error occurs.
LVL 22

Assisted Solution

by:Matt V
Matt V earned 500 total points
ID: 39461767
The other end could also just not be Cisco, sometimes disparate hardware requires that you force the GB connection to Full.

The standard is to set 1Gbps connections to auto, but when it first came out we often had to force it to get it to work with some hardware.
LVL 47

Assisted Solution

by:Craig Beck
Craig Beck earned 500 total points
ID: 39461982
Sometimes when the duplex negotiation fails it will fall-back to half-duplex.  Therefore it's not correct to say that the other end is definitely set to half.  Negotiation could fail for a number of reasons, including manually specifying the speed.

The main reason ISPs specify manual speed and duplex settings is because they want to mitigate any chance of auto-negotiation failure which would result in half-duplex operation and therefore reduce support incidents.

Author Closing Comment

ID: 39463981
I changed it the duplex to FULL and it seems to be working better now.

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

In this article I will be showing you how to subnet the easiest way possible for IPv4 (Internet Protocol version 4). This article does not cover IPv6. Keep in mind that subnetting requires lots of practice and time.
LinkedIn blogging is great for networking, building up an audience, and expanding your influence as well. However, if you want to achieve these results, you need to work really hard to make your post worth liking and sharing. Here are 4 tips that ca…
This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg). If you're looking for how to monitor bandwidth using netflow or packet s…
Monitoring a network: why having a policy is the best policy? Michael Kulchisky, MCSE, MCSA, MCP, VTSP, VSP, CCSP outlines the enormous benefits of having a policy-based approach when monitoring medium and large networks. Software utilized in this v…

622 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question