I have a Cisco 2621XM connected straight to my ISP modem. I have a computer on the second interface of the router.
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 126.96.36.199 188.8.131.52 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
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 Fa0/0as well, we should also be able to determine if you are experiencing performance loss from a duplex mismatch as well.