Cisco Router 1900

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
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interface GigabitEthernet0/0
spped 100
duplex full

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

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pzozulkaAuthor Commented:

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?
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.
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pzozulkaAuthor Commented:
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.
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.
Matt VCommented:
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.
Craig BeckCommented:
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.
pzozulkaAuthor Commented:
I changed it the duplex to FULL and it seems to be working better now.
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