Network communication help

Hi all,
I've been in IT for years on the admin side but i'm new at Cisco configuration. I'm working on my CCNA and i've been going through some router configurations, learning the cmds, etc. I have 2 routers that can communicate with each other via serial. Attached to R2 f0/0 i have attached a switch f0/1 via straight through, then a computer attached to f0/2 on the switch. This is a cut down version of what i'm working on because i'm trying to figure out why my switch can't communicate with my router. I'm sure it's something simple i'm missing but I can't seem to find it. The section i'm studying hasn't gone into switch configuration and vlans but I know i have to setup a vlan which i thought i did properly but still no luck. The interfaces are showing red and they're both set to be up, using a straight through ethernet, but still no luck. Can someone please tell me where i'm going wrong here?

Here's the R2 config:
!
version 12.2
no service timestamps log datetime msec
no service timestamps debug datetime msec
no service password-encryption
!
hostname R2
!
!
!
enable secret 5 $1$mERr$5jbOD5lHVUWxAAsNOD6eO/
enable password password
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0/0
description Private LAN
ip address 25.0.0.1 255.0.0.0
duplex full
speed auto
!
interface FastEthernet0/1
no ip address
duplex auto
speed auto
shutdown
!
interface Serial1/0
description WAN-To-ISP
ip address 24.0.0.2 255.0.0.0
!
interface Serial1/1
no ip address
!
interface Serial1/2
no ip address
!
interface Serial1/3
no ip address
!
ip classless
!
!
!
!
!
!
!
line con 0
line vty 0 4
password telnet
login
!
!
!
end

Here's the switch config
!
version 12.1
no service timestamps log datetime msec
no service timestamps debug datetime msec
no service password-encryption
!
hostname LOCAL-SWITCH
!
!
!
interface FastEthernet0/1
!
interface FastEthernet0/2
!
interface FastEthernet0/3
!
interface FastEthernet0/4
!
interface FastEthernet0/5
!
interface FastEthernet0/6
!
interface FastEthernet0/7
!
interface FastEthernet0/8
!
interface FastEthernet0/9
!
interface FastEthernet0/10
!
interface FastEthernet0/11
!
interface FastEthernet0/12
!
interface FastEthernet0/13
!
interface FastEthernet0/14
!
interface FastEthernet0/15
!
interface FastEthernet0/16
!
interface FastEthernet0/17
!
interface FastEthernet0/18
!
interface FastEthernet0/19
!
interface FastEthernet0/20
!
interface FastEthernet0/21
!
interface FastEthernet0/22
!
interface FastEthernet0/23
!
interface FastEthernet0/24
!
interface Vlan1
ip address 25.0.0.2 255.0.0.0
!
ip default-gateway 25.0.0.1
!
banner motd
Unauthorized access is forbidden

!
line con 0
!
line vty 0 4
login
line vty 5 15
login
!
!
end

Find more posts tagged with

Free for TechExams community: Cybersecurity salary guide

Compare cert salaries and plan your next career move

Button

Comments

Brakarific

I'd need to see "show ip int" output to properly troubleshoot, but just off the cuff, make sure you use the "no shutdown" command on both the router fa 0/0 interface and the Vlan 1 interface on the switch. I know this sounds obvious, but I never put it past myself to forget a little detail like that. Also, a red light generally means a physical layer comm. failure. This generally means the cable terminations are bad.

feenixfire

Brakarific wrote: »

I'd need to see "show ip int" output to properly troubleshoot, but just off the cuff, make sure you use the "no shutdown" command on both the router fa 0/0 interface and the Vlan 1 interface on the switch. I know this sounds obvious, but I never put it past myself to forget a little detail like that.

Hey I'm a n00b so I'm fully expecting this issue to have an obvious solution :-p Here's the show ip int results for the switch and router. The only thing i can think of is the router link show up / down. Do you have to configure some protocol on the router's port? I did run the no shutdown on both interfaces.

Switch results
LOCAL-SWITCH#show ip int
Vlan1 is up, line protocol is up
Internet address is 25.0.0.2/8
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Local Proxy ARP is disabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is disabled
IP fast switching on the same interface is disabled
IP Null turbo vector
IP multicast fast switching is disabled
IP multicast distributed fast switching is disabled
IP route-cache flags are None
Router Discovery is disabled
IP output packet accounting is disabled
IP access violation accounting is disabled
TCP/IP header compression is disabled
RTP/IP header compression is disabled
Probe proxy name replies are disabled
Policy routing is disabled
Network address translation is disable
WCCP Redirect outbound is disabled
WCCP Redirect inbound is disabled
WCCP Redirect exclude is disabled
BGP Policy Mapping is disabled

Router results:
R2#show ip int
FastEthernet0/0 is up, line protocol is down (disabled)
Internet address is 25.0.0.1/8
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is disabled
IP fast switching on the same interface is disabled
IP Flow switching is disabled
IP Fast switching turbo vector
IP multicast fast switching is disabled
IP multicast distributed fast switching is disabled
Router Discovery is disabled
IP output packet accounting is disabled
IP access violation accounting is disabled
TCP/IP header compression is disabled
RTP/IP header compression is disabled
Probe proxy name replies are disabled
Policy routing is disabled
Network address translation is disabled
WCCP Redirect outbound is disabled
WCCP Redirect exclude is disabled
BGP Policy Mapping is disabled
FastEthernet0/1 is administratively down, line protocol is down (disabled)
Internet protocol processing disabled
Serial1/0 is up, line protocol is down (disabled)
Internet address is 24.0.0.2/8
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is disabled
IP fast switching on the same interface is disabled
IP Flow switching is disabled
IP Fast switching turbo vector
IP multicast fast switching is disabled
IP multicast distributed fast switching is disabled
Router Discovery is disabled
IP output packet accounting is disabled
IP access violation accounting is disabled
TCP/IP header compression is disabled
RTP/IP header compression is disabled
Probe proxy name replies are disabled
Policy routing is disabled
Network address translation is disabled
WCCP Redirect outbound is disabled
WCCP Redirect exclude is disabled
BGP Policy Mapping is disabled
Serial1/1 is down, line protocol is down (disabled)
Internet protocol processing disabled
Serial1/2 is down, line protocol is down (disabled)
Internet protocol processing disabled
Serial1/3 is down, line protocol is down (disabled)
Internet protocol processing disabled

KrisA

Brakarific wrote: »

I'd need to see "show ip int" output to properly troubleshoot, but just off the cuff, make sure you use the "no shutdown" command on both the router fa 0/0 interface and the Vlan 1 interface on the switch. I know this sounds obvious, but I never put it past myself to forget a little detail like that. Also, a red light generally means a physical layer comm. failure. This generally means the cable terminations are bad.

Agreed

See also

interface FastEthernet0/1
no ip address
duplex auto
speed auto
shutdown

Tells me the port is turned off.

feenixfire

The fa0/1 on the router isn't being used, i'm using fa0/0. That being said, however, I found the issue. My speed was different for both interfaces so i set speed on the switch and router to 100 and half duplex. I haven't read anything about those yet but can they both be left at auto?

networker050184

feenixfire wrote: »

The fa0/1 on the router isn't being used, i'm using fa0/0. That being said, however, I found the issue. My speed was different for both interfaces so i set speed on the switch and router to 100 and half duplex. I haven't read anything about those yet but can they both be left at auto?

Yep, best bet is to just leave them both to auto.

Brakarific

Glad you found the fault, I thought about negotiation, but didn't think much further. Which is funny, because I've been reading Gary Donahue's book 'Network Warrior' and he goes into detail as to how often he sees speed negotiation issues in one of his first chapters. So kudos to you for being a better troubleshooter than all of us.

pham0329

Hm, can someone explain to me why the speed mismatched would cause the link to go down? I can see packets being dropped due to the duplex mismatch resulting from the speed mismatched, but for the link to go down? From what I remember, if one side can't auto negotiate the speed/duplex, it'll just default to the 10/half, 100/full standard....right?

Brakarific

If it's at 10 half on one side and 100 full on the other side, you will have crazy amounts of packet loss on both ends. The 10 side won't be able to handle the rate at which it will receive data from the 100 side. Plus, if one is half duplex, and the other is full, the full side won't try to avoid collisions. Auto-negotiation doesn't always work as designed, not enough room to write up why, but here is a link -
Duplex mismatch - Wikipedia, the free encyclopedia

pham0329

I can see that on a production network, but on a lab with zero traffic, how does a speed/duplex mismatch bring down a link? My initial thought was stp, but again, not enough traffic to really be a problem

Brakarific

Doesn't have to be a production network. I have seen this twice in my career, and both times it was when I was setting up equipment before a deployment (In my case, Cisco gear wasn't involved, it was Mikrotik). Basically, if you set one as static and the other as auto, it can cause weird things happen, more especially on fiber links, and yet even more so with with Gig interfaces and Non Gig interfaces. Here is how negotiation works, both interfaces start low and go high, sometimes if an interface is statically set to a speed, it will tell the other interface "yeah sure, I can do 10 BaseT, no problem," and the other interface decides to stop there instead of asking about 100 BaseT. This was your problem. In Gary Donahue's book 'Network Warrior', it explains it much better than I can.

Gig interfaces are worse, because starting with 1000BaseT ethernet standards, instead of negotiating bottom up, it negotiates from top speed down. This is how it should have always been in my opinion, but with the two different methods at play, interesting things with auto-negotiation have been known to happen.

pham0329

I was going to give Network Warrior a read once I get through ROUTE, so it's good to know it contains some useful information. However, I think you misunderstood my question. I know that when there's a link/speed mismatch, the link see packet loss or underperform. My question was why in the OP's situation, the link didn't come up just because of the speed mismatch?

Your explanation and reference only explains why speed mismatch cause problems with the link, not why it won't come up because of the mismatch. I've tested this with the 3550s

Sw1 = 10/half, sw2 = 100/full = link came up
Sw1 = 10/half, sw2 = auto (100/full) = link came up

Timber Wolf

I think it may very between devices and IOS's. I had a 2610xm with NM-4e hooked up to a 3550 and the link came up as up down and yelled at me that there was a mismatch and did not fully come up until i changed the settings on both the router and switch.

Brakarific

pham0329-'Your explanation and reference only explains why speed mismatch cause problems with the link, not why it won't come up because of the mismatch.'

Ahh, ok, I see what you are saying. I did misunderstand you. Why the LED would be Red? I have no idea. You are right, it should have just been a mismatch, not a completely dead link. So, I guess this is a question for someone with obviously more experience than the both of us. Looks like Timber Wolf had the same issue, but as for an explanation, I don't have one.