Need help configuring etherchannel/link aggregation

mike2323

Weaksauce
Joined
Sep 2, 2004
Messages
121
I have two switches that I'm trying to aggregate trunk links across. One is a 2900XL and one is a 3560.

On the 3560 I have ports 47 and 48 configured as so:

switchport trunk encapsulation dot1q
switchport mode trunk
channel-group 1 mode on

On the 2900XL I have ports 23 and 24 configured as so:

port group 1 distribution destination
switchport trunk encapsulation dot1q
switchport mode trunk

My system is plugged into port 1 on the 3560. I'm able to ping both the 3560 (192.168.10.2) and the 2900XL (192.168.10.3). For some reason though when I ping the 2900XL the pings are erratic:

Reply from 192.168.10.3: bytes=32 time=1ms TTL=255
Reply from 192.168.10.3: bytes=32 time=1ms TTL=255
Reply from 192.168.10.3: bytes=32 time=8ms TTL=255
Reply from 192.168.10.3: bytes=32 time=28ms TTL=255

Of course the 3560 I'm getting consistent <1ms:

Reply from 192.168.10.2: bytes=32 time=1ms TTL=255
Reply from 192.168.10.2: bytes=32 time<1ms TTL=255
Reply from 192.168.10.2: bytes=32 time<1ms TTL=255
Reply from 192.168.10.2: bytes=32 time=1ms TTL=255

Why is this so? The 2900XL seems very responsive in the CLI but other than that the ping is erratic (on LAN no doubt). Did I mis-configure something? I know I can ignore etherchannel and still have redundancy with the two trunks but I'd just like to see how link aggregation works at the server level, switch level, and router level.
 
maybe you have a loop since your ethernchanel in not setup the right way STP is not working?
 
I have a feeling it may be a loop as the uplink to the router just goes absolutely nuts during the pinging. I'm hoping someone can confirm if my configuration is correct or incorrect.
 
on both switches try the show spanning-tree command and see if you have an interface name of Po1
 
I do. I have a feeling it's just the nature of aggregating the ports. I ran a constant ping and unplugged one of the ports thereby rulling out a loop and still got the ping fluxuations which were usually between 1ms to 40ms. It didn't happen often but it did happen. Ah well.
 
IIRC, the default method is for the switch to forward based on the source. Since you've got it configured to do it based on destination at one end of the EC, that may be part of your problem. Try removing the 'port group 1 dist destination' command from the 2900xl.

As far as the loop goes, the most common thing that creates one with etherchannel is when you're configuring the interfaces on both switches and you dont shut them down before you configure them. You should shut them down on both switches until you finish the config, then bring them up. If you did that, you shouldn't have a spanning-tree loop.
 
It looks like the problem was more with the switch. This 2900XL is returning the ping replies even without the aggregate links so it looks like it wasn't a spanning-tree loop.

My next step is doing aggregate links with my 2651 router. I currently have port f0/0 configured with sub-interfaces for inter-vlan routing. Do I have to move the vlan routing to my 3560 to do aggregate links with the router?
 
I don't think you can do etherchannel on routers unless you have a switch module installed in it. But if thats wrong (or you do have an ESW), you have to assign the ethernet ports to a channel group, and create subinterfaces for trunking on the port channel interface, just as you would do on a regular interface. So you'd have po1.10, instead of fa0/0.10.
 
Boscoh said:
I don't think you can do etherchannel on routers unless you have a switch module installed in it. But if thats wrong (or you do have an ESW), you have to assign the ethernet ports to a channel group, and create subinterfaces for trunking on the port channel interface, just as you would do on a regular interface. So you'd have po1.10, instead of fa0/0.10.

I saw that on a document on Cisco.com. That sucks. I guess no redundancy between the switch and the router unless there is a switch module in the NM port. The ESW modules are expensive too. I wonder if this is possible with the newer ISR routers (1800/2800/3800).
 
I'm pretty sure its the same on the ISR's too.

I think you were on the right track when you asked if you needed to move the inter-vlan routing to the 3560. You could do it on the 3560, and make your links to the router L3 links, and use floating statics, or OSPF if your switch image allows it.
 
Hmm.. thats a good idea. I think I will try that. The 3560 I have is a 48 port PoE switch with the 4 SFP gig ports. It looks to support dynamic routing. That should give me the redundant links though no bonding of the links like etherchannel would give me.
 
It worked. I ended up doing OSPF. It doesn't take more than a second for the links to fail-over.
 
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