Cisco 2821 w/ 16 FastEthernet card and cable modem

[MarkXIX]

I have a Cisco 2821 router that has two gigabit interfaces and a sixteen port fast ethernet card.

What I want to do is attach my Linksys cable modem to one of the gigabit interfaces, set the interface to DHCP, and then NAT behind that interface.

The problem is, when I attach the modem, the gigabit interface shows up/down. I've tried to set speed and duplex manually, but can't get it to work.

Anyone have any ideas?

 

[w0ss]

double check the cable make sure it is good. Did you use a crossover cable? If so just use a normal cable. The cable modem is probably only 10/100 so you should leave it auto on the router.

 

[TheSlamma]

post the cisco config

 

[her209]

You're attaching a Linksys cable modem to the gigabit interface? Are you sure the port on the Linksys cable modem is an Ethernet port?

 

[MarkXIX]

Cable is good, 100% sure of that. Tried another cable too, not the cables.

Yes, it is Linksys cable modem and interface is 10/100. I can plug my laptop directly into the cable and get an IP from the ISP and surf fine. It works fine when I plug it into the wireless router.

 

[MarkXIX]

version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
!
hostname ROUTER
!
boot-start-marker
boot config flash:running-config
boot-end-marker
!
enable password 7 abcdefghijkl
!
no aaa new-model
!
resource policy
!
ip subnet-zero
!
!
ip cef
no ip dhcp use vrf connected
!
!
no ip ips deny-action ips-interface
!
no ftp-server write-enable!
!
no crypto isakmp ccm
!
interface GigabitEthernet0/0
ip address dhcp
duplex full
speed 100
!
interface GigabitEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface FastEthernet1/0
!
interface FastEthernet1/1
!
interface FastEthernet1/2
!
interface FastEthernet1/3
!
interface FastEthernet1/4
!
interface FastEthernet1/5
!
interface FastEthernet1/6
!
interface FastEthernet1/7
!
interface FastEthernet1/8
!
interface FastEthernet1/9
!
interface FastEthernet1/10
!
interface FastEthernet1/11
!
interface FastEthernet1/12
!
interface FastEthernet1/13
!
interface FastEthernet1/14
!
interface FastEthernet1/15
!
interface Vlan1
ip address 10.0.0.2 255.255.255.224
!
ip classless
!
!
ip http server
ip http authentication local
no ip http secure-server
!
control-plane
!
end

 

[imagoon]

interface GigabitEthernet0/0
ip address dhcp
duplex full
speed 100

needs to be:

no ip address
duplex auto
speed auto

you can also add:

G0/1
no shut

but it is not required.

--edit--

You likely need duplex and speed set to auto. There is likely little or no reason at all to set the speeds.

 

[MtnMan]

up/down indicates a layer 1 problem, the cable.

After connecting modem/2811 have you power cycled the modem?

 

[her209]

up/down indicates a layer 1 problem, the cable.

After connecting modem/2811 have you power cycled the modem?

up/down indicates a protocol (Layer 2) problem.

 

[MtnMan]

interface GigabitEthernet0/0
ip address dhcp
duplex full
speed 100

needs to be:

no ip address
duplex auto
speed auto

you can also add:

G0/1
no shut

but it is not required.

--edit--

You likely need duplex and speed set to auto. There is likely little or no reason at all to set the speeds.

But he will need the "ip address dhcp", but agree on the speed auto.

 

[MtnMan]

up/down indicates a protocol (Layer 2) problem.

Nope, it up (layer 2), down (layer 1)

Go to a working router, disconnect a cable then do a "show ip int brief" and see for yourself.

 

[MtnMan]

What Linksys cable modem are you using? Their old version is 10 meg, not 10/100.

 

[her209]

Nope, it up (layer 2), down (layer 1)

Go to a working router, disconnect a cable then do a "show ip int brief" and see for yourself.

No, its line status / protocol status.

You can never have a protocol status of up with a line status of down.

 

[MtnMan]

No, its line status / protocol status.

You can never have a protocol status of up with a line status of down.

If you configure and interface with an address and do a no shut, you will get an up/down
connect a cable to a valid device, and it goes up/up

got a router or switch, try it
got GNS3, try it
got Packet Tracer, try it

 

[spidey07]

If you configure and interface with an address and do a no shut, you will get an up/down
connect a cable to a valid device, and it goes up/up

got a router or switch, try it
got GNS3, try it
got Packet Tracer, try it

Um, no. UP/down is L1 up, L2 down.

LAB6509(config)#int f9/47

LAB6509(config-if)#ip add 1.1.1.1 255.255.255.0
LAB6509(config-if)#no shut
LAB6509(config-if)#do sh int f9/47
FastEthernet9/47 is down, line protocol is down (notconnect)
Hardware is C6k 100Mb 802.3, address is
Internet address is 1.1.1.1/24

 

[spidey07]

No, its line status / protocol status.

You can never have a protocol status of up with a line status of down.

Actually you can. A VLAN SVI will show up/down if there are no ports on the switch active in that vlan. Or other WAN circuits where HDLC, Frame-relay, ATM, etc didn't come up. You'll have L1, but no L2.

doh, re-read what you said. Yes, you can never have L2 up without a good L1.

 

[MtnMan]

Here is the configuration
--------------------------------------
interface FastEthernet0/0
ip address 172.17.20.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 192.168.100.1 255.255.255.0
duplex auto
speed auto
!
Here is the "sh ip int brief"
----------------------------------
sh ip int brief
Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 172.17.20.1 YES manual up up (cable connected to switch)

FastEthernet0/1 192.168.100.1 YES manual up down (no cable connected)You figure it out.

up/down is a layer 1 problem

 

[spidey07]

Here is the configuration
--------------------------------------
interface FastEthernet0/0
ip address 172.17.20.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 192.168.100.1 255.255.255.0
duplex auto
speed auto
!
Here is the "sh ip int brief"
----------------------------------
sh ip int brief
Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 172.17.20.1 YES manual up up (cable connected to switch)

FastEthernet0/1 192.168.100.1 YES manual up down (no cable connected)You figure it out.

up/down is a layer 1 problem

You're looking at a different command. You're looking at show ip interface brief, you're looking at layer3. This is very different than a "show interface" which shows L1/L2. "show ip int brief" says nothing about L1/L2, only L3.

UP/Down on "show interface" is good L1, no L2. UP/Down on "show ip int brief" says "IP is running on this interface, but the L3 protocol is actually down"

 

[w0ss]

You're looking at a different command. You're looking at show ip interface brief, you're looking at layer3. This is very different than a "show interface" which shows L1/L2. "show ip int brief" says nothing about L1/L2, only L3.

UP/Down on "show interface" is good L1, no L2. UP/Down on "show ip int brief" says "IP is running on this interface, but the L3 protocol is actually down"

While I could be wrong... when you are speaking of ethernet UP/DOWN has always meant a layer 1 problem. In every other type of interface I know with cisco it usually means layer 2 not sure why cisco did that with ethernet. As previously suggested go look at a switch port/router ethernet port that has the cable unplugged it will be UP/DOWN.


The reason I mentioned the cable type is that on all cisco gigabit equipment that I know of when you hard code the speed/duplex it will disable auto MDI/MDIX

EDIT:I took a look and it appears this is not always the case! I checked some of my switches and on 4500/6500/nexus it looks like the ports are down/down but on routers even with switch NM modules the ports are up/down.

 

[MtnMan]

You're looking at a different command. You're looking at show ip interface brief, you're looking at layer3. This is very different than a "show interface" which shows L1/L2. "show ip int brief" says nothing about L1/L2, only L3.

UP/Down on "show interface" is good L1, no L2. UP/Down on "show ip int brief" says "IP is running on this interface, but the L3 protocol is actually down"

OK, show interface, same configuration as before
-------------------------------------
Router#sh int
FastEthernet0/0 is up, line protocol is up (connected)
Hardware is Lance, address is 0001.c7ce.9a01 (bia 0001.c7ce.9a01)
Internet address is 172.17.20.1/24
<snip>

FastEthernet0/1 is up, line protocol is down (disabled)
Hardware is Lance, address is 0001.c7ce.9a02 (bia 0001.c7ce.9a02)
Internet address is 192.168.100.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,


up/up working
up/down no cable (layer 1)

or

Router#sh ip int brief
Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 172.17.20.1 YES manual up up

FastEthernet0/1 192.168.100.1 YES manual up down

 

[spidey07]

Then you have a bug. If the cable is unplugged you have no L1 and it should be down/down. I tried it on a 7300, an ASR1002 and a 3800, all show down/down with no cable and IP configured and not admin down.

 

[MtnMan]

Then you have a bug. If the cable is unplugged you have no L1 and it should be down/down. I tried it on a 7300, an ASR1002 and a 3800, all show down/down with no cable and IP configured and not admin down.

Nope, no bug. this is on a 2811 router.

A configured serial without a cable will show down/down
A configured ethernet without a cable will show up/down

A configured serial with a cable but not receiving a clock will show up/down

OP is talking about gigabit ethernet, unless gigabit works different than fast ethernet.

 

[jlazzaro]

Then you have a bug. If the cable is unplugged you have no L1 and it should be down/down. I tried it on a 7300, an ASR1002 and a 3800, all show down/down with no cable and IP configured and not admin down.

now ladies...

it ultimately comes down to the device type, and possibly the IOS version and where the port lies (module, on board, etc). the interface status/protocol behavior will vary between switch ports, routed interfaces, L3 interfaces, and router interfaces.

in the OPs case, the status being UP/down simply means the interface hardware is currently active, but does not imply something is connected. it's L1 is active, but does not assume a L1 link. I have seen both up/down and down/down with nothing connected, its not a single behavior across the board and will vary between scenarios.

what IOS is on your 3800, onboard interface?

edit:
http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1904.html#wp1020996

 

[MtnMan]

So, if the OP ever returns, disconnect the cable and do a show interface or show ip int brief and post your results.

My bet is up/down :whiste:

 

[alkemyst]

Here is the configuration
--------------------------------------
interface FastEthernet0/0
ip address 172.17.20.1 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 192.168.100.1 255.255.255.0
duplex auto
speed auto
!
Here is the "sh ip int brief"
----------------------------------
sh ip int brief
Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 172.17.20.1 YES manual up up (cable connected to switch)

FastEthernet0/1 192.168.100.1 YES manual up down (no cable connected)You figure it out.

up/down is a layer 1 problem

Are you trying to troll us? Are you even a CCNA?

It's Layer 1/Layer 2

This is all verifiable through cisco's line interface whitepages.