I have a Cisco 2621XM connected straight to my ISP modem. I have a computer on the second interface of the router.
Topology:
ISP -> Modem -> Cisco Router -> Computer
When I run a speedtest on my computer I get 30/10. When I connect my computer straight to my modem I get 100/10. I also have another Cisco Router, 871. Same exact results, I get 30/10 when I connect my computer to it.
I'm starting to think that it's a default setting that comes baked into the router? Here's my config:
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Router
!
boot-start-marker
boot-end-marker
!
enable secret 5 <REMOVED>
!
no aaa new-model
!
resource policy
!
no network-clock-participate slot 1
no network-clock-participate wic 0
ip subnet-zero
ip cef
!
no ip dhcp use vrf connected
ip dhcp excluded-address 10.4.4.1 10.4.4.100
!
ip dhcp pool ALL_ACCESS
network 10.4.4.0 255.255.255.0
dns-server 8.8.8.8 8.8.4.4
default-router 10.4.4.1
!
interface FastEthernet0/0
ip address 10.4.4.1 255.255.255.0
ip nat inside
speed 100
full-duplex
!
interface Serial0/0
no ip address
shutdown
!
interface FastEthernet0/1
ip address dhcp
ip nat outside
duplex auto
speed auto
!
ip classless
!
no ip http server
no ip http secure-server
ip nat inside source list 1 interface FastEthernet0/1 overload
!
access-list 1 permit 10.4.4.0 0.0.0.255
!
control-plane
!
line con 0
logging synchronous
line aux 0
line vty 0 4
login
line vty 5 181
login
!
end
Output from show interface
:
Router#sh interfaces FastEthernet0/1
FastEthernet0/1 is up, line protocol is up
Hardware is AmdFE, address is 000e.3836.ff41 (bia 000e.3836.ff41)
Internet address is xxx.xxx.xxx.xxx/xx
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, 100BaseTX/FX
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 1/75/128247/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 51000 bits/sec, 41 packets/sec
5 minute output rate 4000 bits/sec, 6 packets/sec
16778657 packets input, 2855708480 bytes
Received 5967982 broadcasts, 0 runts, 0 giants, 0 throttles
69379 input errors, 0 CRC, 0 frame, 15274 overrun, 54105 ignored
0 watchdog
0 input packets with dribble condition detected
3231581 packets output, 590804149 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 babbles, 0 late collision, 0 deferred
484 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
sh interfaces FastEthernet0/1 status
- Doesn't output anything
show interfaces Fa0/0
as well, we should also be able to determine if you are experiencing performance loss from a duplex mismatch as well.