Category Archives: Troubleshooting


Cisco 7609 10 Gig Link Aggregation

I ran into an interesting problem last week, and I found very little information on the internet about it. I will share it here, in the hope that it will help someone else.


Working with a newer product, I created a 10 Gig Link Aggregation configuration on my Cisco 7609 WS-X6708-10GE cards.

Cisco Config

interface Port-channel1
description TA5000 40 Gig LAG
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 10-20
switchport mode trunk
no ip address
mls qos trust cos
spanning-tree bpdufilter enable
spanning-tree bpduguard enable
lacp max-bundle 4

When I added the second link to the group, the Cisco kept putting the link into an alternate group!

Port-channel: Po1A

Age of the Port-channel   = 0d:00h:02m:47s
Logical slot/port   = 14/6          Number of ports = 1
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
<  0     FF     Te1/3    Active    8

Time since last port bundled:    0d:00h:02m:45s    Te1/3

I searched the web for any indication of what the A meant on the end of the port-channel group, but I came up empty. All I knew was that my config looked good, and the Cisco would not add the second link into the group. The only thing I could find about this “alternate” group was, “if something on the other end doesn’t match exactly, the Cisco will declare the link in a new group”.

Armed with that little information, the search begins.

Partner Information

Doing a ‘show lacp neighbor detail’ gave me the information I needed to find the issue.

          Partner               Partner                     Partner
Port      System ID             Port Number     Age         Flags
Te1/3     00001,00a0.c8c8.3edd  0x3               0s        FA

          LACP Partner         Partner         Partner
          Port Priority        Oper Key        Port State
          65535                0x1             0x3F

          Port State Flags Decode:
          Activity:   Timeout:   Aggregation:   Synchronization:
          Active      Long       Yes            Yes

          Collecting:   Distributing:   Defaulted:   Expired:
          Yes           Yes             No           No
          Partner               Partner                     Partner
Port      System ID             Port Number     Age         Flags
Te1/4     00001,00a0.c8c8.414d  0xD               0s        FA

As you can see, the System ID’s for each link being reported in the LACP protocol do not match. Now, in this case, this is true, as the end device is in a multi-chassis LAG configuration. In order to work with the Cisco, the System ID’s must match. The Alcatel 7750 does not do this check.

Changing the System ID, allows the lag group to come up.

Port-channel: Po1    (Primary Aggregator)

Age of the Port-channel   = 9d:20h:10m:33s
Logical slot/port   = 14/5          Number of ports = 2
Port state          = Port-channel Ag-Inuse 
Protocol            =   LACP

Ports in the Port-channel: 

Index   Load   Port     EC state        No of bits
  0     55     Te1/3    Active            4
  1     AA     Te1/4    Active            4

Time since last port bundled:    3d:17h:48m:54s    Te1/4
Time since last port Un-bundled: 3d:18h:09m:43s    Te1/3

Protected: Using Wireshark to Identify Packet Loss on Mediaroom IGMP Flows

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Wireshark Filters – PPPoE, DHCP & VLAN ID

Using Filters

Wireshark comes standard with some very good filters. Filtering the displayed packets allows you to focus on relevant information located within the capture.

In this post, I’m going to show you how to filter out DHCP exchanges, PPPoE exchanges and VLAN’s.

Setting the Filter

Click on the filter field to enter the filter options manually, or press the Expression button to start the Wireshark filter expression box. When you are unfamiliar with which protocols you want to filter on, the Expression window allows you to choose each dissector and how the filter is applied (equals, contains, matches, less than, greater than).


Filtering on a VLAN tag is really quite simple using Wireshark’s built in dissector.

In the filter field, type in: == <put your vlan id here>

Press return to start the filtering process. Wireshark will then go through each packet in the capture file and display only those packets that match the criteria.


Filtering for DHCP packets is pretty easy in Wireshark also.

In the filter field, type in:


Press return to start the filtering process.


PPPoE is a little trickier to decode the entire process, as there are several steps in the process from PADI to IPCP negotitation.

In the filter field, type in:

pppoed or lcp or ipcp or pap or chap

Press return to start the filtering process.

This filter has several components that allow you to capture the entire PPPoE process from beginning to end.
The first part of the filter, pppoed, filters out the PADI, PADO, PADR & PADS exchange. The next step, lcp,  in the process is to negotiate the MTU size, magic number and authentication protocol.

After the lcp negotiation is complete, the user is authenticated via PAP or CHAP. If you have a username or password issue in the modem or BRAS, this is where you will see the negotiation fail.

Once the user is authenticated, we can finally start the IP address negotiation. The ipcp filter will show you the IP address negotiation.

Now that the user is up and authenticated, you will see LCP Echoes between the modem and BRAS. Settings in the modem and BRAS will determine the frequency and size of the echo messages.

Keep in mind that the LCP echo process uses a single ended state machine. What this means is that each end of the link, the modem and the BRAS, keep track of their LCP echoes independently of each other. Whenever either end loses enough consecutive echoes (configurable on the BRAS), it will tear the link down using a PADT. This is a major difference between DHCP leases and PPPoE sessions, either end can tear down the connection. Once a DHCP server issues a lease, that lease is bound until timeout or a DHCP release message is sent.