From: Guyler, Rik (rguyler@shp-dayton.org)
Date: Mon Aug 13 2007 - 22:09:54 ART
Maybe this is part of what you want (written to answer a quastion about STP
convergence with regard to an Etherchannel):
STP should *not* come into play where a port channel is concerned unless the
port channel only has a single remaining physical interface left in the
bundle. The default STP cost for a gig link is 4 but when an Etherchannel
is formed, the default STP cost for the bundle is 3 and that doesn't change
whether the bundle has 2, 3 or 4 physical links. But when the bundle drops
down to its last active physical link, the STP cost of the bundle becomes 4
again so STP should trigger a TCN (topology change notification).
Below, I show that the STP cost of the Etherchannel is the same regardless
if the bundle has 2 - 4 active ports:
MB0GCRE-DSW-01#sh spann int po1
Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
VLAN0001 Desg FWD 3 128.1665 P2p
VLAN0492 Desg FWD 3 128.1665 P2p
VLAN0493 Root FWD 3 128.1665 P2p
VLAN0494 Desg FWD 3 128.1665 P2p
VLAN0495 Root FWD 3 128.1665 P2p
VLAN0496 Desg FWD 3 128.1665 P2p
VLAN0497 Root FWD 3 128.1665 P2p
VLAN0498 Desg FWD 3 128.1665 P2p
VLAN0499 Root FWD 3 128.1665 P2p
VLAN0500 Desg FWD 3 128.1665 P2p
VLAN0502 Desg FWD 3 128.1665 P2p
VLAN0503 Root FWD 3 128.1665 P2p
VLAN0504 Desg FWD 3 128.1665 P2p
VLAN0505 Root FWD 3 128.1665 P2p
VLAN0507 Root FWD 3 128.1665 P2p
VLAN0600 Root FWD 3 128.1665 P2p
MB0GCRE-DSW-01#sh ether 1 summ
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
Number of channel-groups in use: 38
Number of aggregators: 38
Group Port-channel Protocol Ports
------+-------------+-----------+---------------------------------------
------+-------------+-----------+--------
1 Po1(SU) PAgP Gi2/1(P) Gi2/2(P) Gi6/1(P) Gi6/2(P)
MB0GCRE-DSW-01#sh spann int po35
Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
VLAN0492 Desg FWD 3 128.1693 P2p
VLAN0494 Desg FWD 3 128.1693 P2p
MB0GCRE-DSW-01#sh ether 35 summ
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
M - not in use, minimum links not met
u - unsuitable for bundling
w - waiting to be aggregated
Number of channel-groups in use: 38
Number of aggregators: 38
Group Port-channel Protocol Ports
------+-------------+-----------+---------------------------------------
------+-------------+-----------+--------
35 Po35(SU) LACP Gi4/27(P) Gi4/28(P)
MB0GCRE-DSW-01#sh spann int g5/1
Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
VLAN0504 Desg FWD 4 128.513 Edge P2p
MB0GCRE-DSW-01#sh run int g5/1
Building configuration...
Current configuration : 201 bytes
!
interface GigabitEthernet5/1
switchport
switchport access vlan 504
switchport mode access
no ip address
no snmp trap link-status
spanning-tree portfast
end
****************************************************************************
********
This next snippet shows what happens to the STP cost of a two-port
Etherchannel when it goes down to a single link (had to change to a
non-production device to show this ;-):
MB0GA-OS-01#sh ether 1 summ
Flags: D - down P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+---------------------------------------
------+-------------+-----------+--------
1 Po1(SU) PAgP Gi0/21(P) Gi0/22(P)
MB0GA-OS-01#sh spann int po1
Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
VLAN0001 Desg FWD 3 128.56 P2p
VLAN0100 Desg FWD 3 128.56 P2p
VLAN0101 Desg FWD 3 128.56 P2p
MB0GA-OS-01#conf t
Enter configuration commands, one per line. End with CNTL/Z.
MB0GA-OS-01(config)#int g0/22
MB0GA-OS-01(config-if)#shut
MB0GA-OS-01(config-if)#^Z
MB0GA-OS-01#
MB0GA-OS-01#sh spann int po1
Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
VLAN0001 Desg FWD 4 128.56 P2p
VLAN0100 Desg FWD 4 128.56 P2p
VLAN0101 Desg FWD 4 128.56 P2p
MB0GA-OS-01#sh ether 1 summ
Flags: D - down P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+---------------------------------------
------+-------------+-----------+--------
1 Po1(SU) PAgP Gi0/21(P) Gi0/22(D)
MB0GA-OS-01#conf t
Enter configuration commands, one per line. End with CNTL/Z.
MB0GA-OS-01(config)#int g0/22
MB0GA-OS-01(config-if)#no shut
MB0GA-OS-01(config-if)#^Z
MB0GA-OS-01#sh ether 1 summ
Flags: D - down P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+---------------------------------------
------+-------------+-----------+--------
1 Po1(SU) PAgP Gi0/21(P) Gi0/22(P)
MB0GA-OS-01#sh spann int po1
Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
VLAN0001 Desg FWD 3 128.56 P2p
VLAN0100 Desg FWD 3 128.56 P2p
VLAN0101 Desg FWD 3 128.56 P2p
MB0GA-OS-01#
Rik
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
slevin kremera
Sent: Monday, August 13, 2007 8:43 PM
To: Ben
Cc: Cisco certification
Subject: Re: etherchannel and spanning-tree forwarding state iewb-v3 vol2
lab 4 task1.1
thks guys...i understood the trick behind configuring etherchannel
On 8/13/07, Ben <ccieben@cox.net> wrote:
>
> Hi Slevin,
>
> With default settings, if you had two links between switches - one of
> them would be blocked on one side. If you bond the links using
> etherchannel, they are treated as one logical link - hence both are
> forwarding.
>
> Using NM-16ESW - SW1 & SW2 connected:
> Fa2/1 <-->Fa2/1
> Fa2/2 <-->Fa2/2
>
> Before Etherchannel:
> Rack1SW2#show spanning-tree vlan 10 brief | be Inter
> Interface Designated
> Name Port ID Prio Cost Sts Cost Bridge ID
> Port ID
> -------------------- ------- ---- ----- --- ----- --------------------
> -------
> FastEthernet2/1 128.82 128 19 FWD 0 32768 cc06.0c3c.0002
> 128.82
> FastEthernet2/2 128.83 128 19 BLK 0 32768 cc06.0c3c.0002
> 128.83
>
> After Etherchannel
> Rack1SW2#show spanning-tree vlan 10 brief | be Inter
> Interface Designated
> Name Port ID Prio Cost Sts Cost Bridge ID
> Port ID
> -------------------- ------- ---- ----- --- ----- --------------------
> -------
> Port-channel1 129.65 128 12 FWD 0 32768 cc06.0c3c.0002
> 129.65
>
> HTH
> Ben
> slevin kremera wrote:
> > what relation or effect does etherchannel configuration have in
> > relation
> to
> > spanning tree forwarding state
> >
> > ____________________________________________________________________
> > ___ Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
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