[c-nsp] Port-Channel Problem

[Dan Armstrong]

Riddle me this.

I have 1 physical link, and a port-channel interface operating in PAgP mode.

interface GigabitEthernet1/21
no ip address
 switchport
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 50,80,119,300-304,349,412,420,440,444,446,447
 switchport trunk allowed vlan add 449,500,503,616,620,900
 switchport mode trunk
 channel-group 10 mode desirable
end

interface Port-channel10
 no ip address
 switchport
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 50,80,119,300-304,349,412,420,440,444,446,447
 switchport trunk allowed vlan add 449,500,503,616,620,900
 switchport mode trunk


metro2.tor-Front[7609]#sh int po10
Port-channel10 is up, line protocol is up (connected)
  Hardware is EtherChannel, address is 0015.f91d.5c8e (bia 0015.f91d.5c8e)
  Description: GEC to metro1.tor-Mowat [Port-channel10]
  MTU 9216 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 104/255, rxload 202/255


Life was good, then:


2 problems.  I first tried to change to LACP:

metro2.tor-Front[760(config-if)#channel-group 10 mode ?
  active     Enable LACP unconditionally
  auto       Enable PAgP only if a PAgP device is detected
  desirable  Enable PAgP unconditionally
  on         Enable Etherchannel only
  passive    Enable LACP only if a LACP device is detected

metro2.tor-Front[760(config-if)#channel-group 10 mode active


The interface bounced, and went straight back into PAgP mode..... 

I tried it several times.  #$S%E$@#$, always back to PAgP..... 
"channel-group 10 mode desirable"


Second problem:

I tried a second link anyway, and when I added a second link into the 
PAgP group, the rely on the port-channel interface started dropping like 
a stone,  packets were dropping all over the place and even though 
everything seemed to be up, speed, duplex, vlans, configuration 
perfectly matched between the underlying physical interfaces & the 
port-channel interface.... the po interface was a mess.  The new 
physical link on it's own is clean as a whistle when I setup a test 
vlan, or set both sides up as routed interfaces....

Anybody have any light to shed?