Simple Question 4

[Niall22]

I don't know a whole lot about Cisco switches sorry forgive me if this question is stupid.

We have about 10 2924 Catalyst switches which connect to our backbone (3548 Catalyst). I am assuming that there is some port grouping set up because each switch connects to the backbone through a pair of ethernet connections. What I have noticed lately is that some of the ports that connect to the backbone, on a few of the switches, are flashing from green to orange to green instead of being the usual solid green color. Can someone please tell me what this indicates? Does it have anything to do with collisions?

Thanks, Niall

 

[dibbkd]

I've seen the ports flashing when there is a network "loop".
You say you have all the 2924's connected to the 3548, is this through copper (RJ-45) connections or fiber? I believe the 3548 has two GBIC fiber uplinks and 48 copper.

A network loop means that there is a switch connected multiple times to another switch, and the traffic doens't know where to go since there are multiple paths.

Just some of the ports flash green/oranage, correct?

 

[Niall22]

They are connected using copper RJ-45, no gigabit connections. How could a network loop exist? All the 2924's connect into ports on the backbone through a pair of RJ-45s.

Correct, just some of the ports are flashing green/orange.

Would this have an effect on network performance? Niall

 

[dibbkd]

When you say that the 2924's are connected into the ports through a pair of RJ-45's, do you mean you have two RJ-45's going to each 2924, or where you using "pair" figuratively?

If you really do have two CAT5 cables going to a 2924 (without trunking or etherchannel), you will have a loop.

Another thing to check, and I don't know for sure if this would cause a loop, but check the IP's of all the switches, make sure you have no duplicates.

Let us know what you find, I'm curious now. Also, do you have any of the 2924's connected to each other? If so, and they both go back to the 3548, that would cause a loop.

 

[BuckWeet]

Can you get us the configs of the switches? Look for a "port group" command under the interfaces that hook between switches..


BuckWeet

 

[Niall22]

Yes, the switches are connected to the backbone using 2 RJ-45s. Here's the config for the Catalyst 3548 (Backbone) switch. It's really long and there is definitely some port grouping going on. None of the 2924s are connected to each other. They all run back to the 3548 switch. There don't seem to be any switches with duplicate IP addresses either. This network was initially installed and configured 2 years ago by Compaq and I assume they know what they're doing.

CATALYST 2548 CONFIG:

version 12.0
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname DABackbone3548
!
no logging console
enable secret 5 $1$5JUq$g.7HH/QuNyWAkWtTC6Fvc.
!
clock timezone est -5
!
ip subnet-zero
!
!
interface FastEthernet0/1
!
interface FastEthernet0/2
!
interface FastEthernet0/3
duplex full
speed 100
!
interface FastEthernet0/4
duplex full
speed 100
!
interface FastEthernet0/5
duplex full
speed 100
!
interface FastEthernet0/6
duplex full
speed 100
!
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
duplex full
speed 100
port group 1 distribution destination
!
interface FastEthernet0/24
duplex full
speed 100
port group 1 distribution destination
!
interface FastEthernet0/25
duplex full
speed 100
port group 2 distribution destination
!
interface FastEthernet0/26
duplex full
speed 100
port group 2 distribution destination
!
interface FastEthernet0/27
duplex full
speed 100
port group 3 distribution destination
!
interface FastEthernet0/28
duplex full
speed 100
port group 3 distribution destination
!
interface FastEthernet0/29
duplex full
speed 100
port group 11 distribution destination
!
interface FastEthernet0/30
duplex full
speed 100
port group 11 distribution destination
!
interface FastEthernet0/31
duplex full
speed 100
port group 4 distribution destination
!
interface FastEthernet0/32
duplex full
speed 100
port group 4 distribution destination
!
interface FastEthernet0/33
duplex full
speed 100
port group 5 distribution destination
!
interface FastEthernet0/34
duplex full
speed 100
port group 5 distribution destination
!
interface FastEthernet0/35
duplex full
speed 100
port group 6 distribution destination
!
interface FastEthernet0/36
duplex full
speed 100
port group 6 distribution destination
!
interface FastEthernet0/37
duplex full
speed 100
port group 7 distribution destination
!
interface FastEthernet0/38
duplex full
speed 100
port group 7 distribution destination
!
interface FastEthernet0/39
duplex full
speed 100
!
interface FastEthernet0/40
duplex full
speed 100
!
interface FastEthernet0/41
duplex full
speed 100
port group 8 distribution destination
!
interface FastEthernet0/42
duplex full
speed 100
port group 8 distribution destination
!
interface FastEthernet0/43
duplex full
speed 100
port group 9 distribution destination
!
interface FastEthernet0/44
duplex full
speed 100
port group 9 distribution destination
!
interface FastEthernet0/45
duplex full
speed 100
port group 10 distribution destination
!
interface FastEthernet0/46
duplex full
speed 100
port group 10 distribution destination
!
interface FastEthernet0/47
duplex full
speed 100
port group 12 distribution destination
!
interface FastEthernet0/48
duplex full
speed 100
port group 12 distribution destination
!
interface GigabitEthernet0/1
!
interface GigabitEthernet0/2
!
interface VLAN1
ip address 10.2.1.5 255.255.255.0
no ip directed-broadcast
no ip route-cache
!
ip default-gateway 10.2.1.1
snmp-server engineID local 000000090200000142F927C0
snmp-server community public RO
snmp-server community dur55ccac RW
snmp-server chassis-id 0x17
!
line con 0
transport input none
stopbits 1
line vty 0 4
login
line vty 5 15
login
!
end

Here is the config of one of the Catalyst 2924s:

version 12.0
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname DA4th1-2924
!
enable secret 5 $1$ZOY1$9tNdoqM72HJFnCbuxpO0l.
!
!
ip subnet-zero
!
!
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
port group 1 distribution destination
!
interface FastEthernet0/24
port group 1 distribution destination
!
interface VLAN1
ip address 10.2.1.6 255.255.255.0
no ip directed-broadcast
no ip route-cache
!
ip default-gateway 10.2.1.1
snmp-server engineID local 0000000902000001428DB340
snmp-server community public RO
snmp-server community dur55ccac RW
snmp-server chassis-id 0x0E
!
line con 0
transport input none
stopbits 1
line vty 0 4
login
line vty 5 9
login
!
end

As you can see the last 2 ports on each 2924 switch are configured for port grouping. These are the ports that are connected to the 3548. Let me know if anything jumps out at you.

Niall

 

[dibbkd]

Niall22, right off the bat nothing jumps out, but if you unplug one of the CAT5 that is supposed to be grouped, and move the other CAT5 to a non-grouped port, does it turn solid green and start working? Try that, if that works, then you definately know you have something wrong with grouping.
I'm going to be doing exactly the same thing you are in the next few days here, but with fiber links instead of copper, but essentially the same.
Also, next time you paste your configs, "X" out or change your IP addresses (even though it's the private range) and don't show your SMTP community strings.

 

[Niall22]

DOH! I didn't think to remove private IPs or SNMP strings. Is there any way to edit a message in this forum?

I don't really want to play with our switches... we have about 150+ users so I don't want to mess anything up. I may try what you suggested some day after hours if I have time. I was simply curious if anyone has ever had experienced these symptoms before with Cisco switches and if it affects network performance.

Thanks for all your help. Niall

 

[dibbkd]

Hey, you said you didn't want to do this while users were online... so these switches that are flashing green/orange are working?

One thing to check is this too: You have ports 31 and 32 setup as group 4. Make sure these two CAT5's go back to the same switch... know what I mean? If you or someone else moved the cables around, then the two ports you have setup as a group won't be going back to the same switches, and would cause a loop and the flashing lights you describe.

And, I don't know how to edit a post. Since you have private addressing, you're probably safe enough from hackers, but I'd always remove that stuff of course.

 

[Niall22]

Dibbkd,

Yes these switches seem to be working fine. I was simply curious about the lights flashing on some of the ports. I will check to make sure they all match up properly sometime. As far as know though, no one has ever touched them or moved the cables around.

Thanks again for all your help.
Niall

 

[bythespy]

I would check to make sure that each of the cables in a group go to the same switch as a previous poster suggested.

Is there a pattern? ie
Does only one port in a group change colors?
Do all the groups have at least one port that changes color?
Do they do it all the time, randomly or at specific times?

The fact that you have these lights changing from green to orange, almost guarantees that you have a loop of some kind, it may be difficult to track down but I will bet it is impacting performance more than you realize.



Mspivey
CCNP

 

[MJewell]

My immediate though is that on the 3548 your forcing the ports to 100 full, do the same on the 2924's, for some reason Cisco's never auto-negotiate very well...

If your getting duplex errors on the switches that would cause the leds to blink amber... Assuming your seeing the blinking during peek hours, I would check the port counters:
sh int faX/0

Mike

 

[krr]

Mike is on the right track.

Setting speed and duplex (here on the 3548) disables autonegotiation. The 2924 tries to negotiate, doesn't get an answer and defaults to half duplex. The resulting duplex mismatch produces lots of errors - the more traffic the more errors. The yellow light indicates excessive errors.

Do a show cdp neighbour on the 3548 and it will tell you about all the duplex mismatches.

General rule: Always set both sides of a link to full duplex or leave both sides to autonegotiation.

Cheers *Rob

 

[Degg]

you can also look at the switch logs and see if they say 'duplex mismatch port x' and that will tell you about a duplex mismatch. Degg
Network Administrator

 

[Niall22]

Thanks for the replies guys!
I'm going to set both sides of the groups to FULL DUPLEX.
One question though, do I have to reboot the switches after making thoses changes or will they be in effect immediately?

Thanks again,
Niall

 

[BuckWeet]

Changes take effect immediately.


BuckWeet