Questions regading PAgP and STP output.

[chandra_rc16]

I'm learning etherchannels, so got the below doubts while practicing. Please help.          

Here is my topology.

Here is the output of "show etherchannel" on Switch1 (Root switch)

Switch1#show etherchannel

                Channel-group listing:

                ----------------------

Group: 1

----------

Group state = L2

Ports: 4 Maxports = 8

Port-channels: 1 Max Portchannels = 1

Protocol:   PAGP

Group: 2

----------

Group state = L2

Ports: 2 Maxports = 8

Port-channels: 1 Max Portchannels = 1          //What does this line mean? I really didn't understood this line.

Protocol:   PAGP

-----------------------------------------------------------------

Here is the output of "show etherchannel summary" on Switch1/Rootswitch

Switch1#show etherchannel sum

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: 2    

Number of aggregators:           2             // Is this the total number of channels on the switch?

Group  Port-channel  Protocol    Ports

------+-------------+-----------+----------------------------------------------

1      Po1(SU)           PAgP   Fa0/1(P) Fa0/2(P) Fa0/5(I) Fa0/6(I)

2      Po2(SU)           PAgP   Fa0/3(P) Fa0/4(P)

-------------------------

Here Fa0/5,Fa0/6 will also go to Switch3, here is the output of show etherchannel on swtich3

Switch3#show etherchannel

                Channel-group listing:

                ----------------------

Group: 1

----------

Group state = L2

Ports: 2 Maxports = 8

Port-channels: 1 Max Portchannels = 1

Protocol:   PAGP

Group: 2

----------

Group state = L2

Ports: 2 Maxports = 8

Port-channels: 1 Max Portchannels = 1

Protocol:   PAGP

--------------------------------------------------------

Here is the output of show etherchannel summary on switch3

Switch3#show etherchannel sum

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: 2

Number of aggregators:           2

Group  Port-channel  Protocol    Ports

------+-------------+-----------+----------------------------------------------

1      Po1(SD)           PAgP   Fa0/5(I) Fa0/6(I)

2      Po2(SU)           PAgP   Fa0/3(P) Fa0/4(P)

------------------------------------------------------------------------------------

The output of show spanning-tree on both Switch1 & Switch3 doesn't show the Fa0/5,Fa0/6 as port channels, it is showing as individual ports, Why?

spanning-tree output from Switch3:

Switch3#show spanning-tree

VLAN0001

  Spanning tree enabled protocol ieee

  Root ID    Priority    32769

             Address     0001.9713.EEAD

             Cost        9

             Port        25(Port-channel 2)

             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)

             Address     00E0.F710.1331

             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

             Aging Time  20

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/5            Altn BLK 19        128.5    P2p

Fa0/6            Altn BLK 19        128.6    P2p                    //Why these two ports are not showing up as a Portchannel?

Po2              Root FWD 9         128.25   Shr

spanning-tree output from Switch1:

Switch1#show spanning-tree

VLAN0001

  Spanning tree enabled protocol ieee

  Root ID    Priority    32769

             Address     0001.9713.EEAD

             This bridge is the root

             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)

             Address     0001.9713.EEAD

             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

             Aging Time  20

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/6            Desg FWD 19        128.6    P2p

Fa0/5            Desg FWD 19        128.5    P2p

Fa0/10           Desg FWD 19        128.10   P2p

Po1              Desg FWD 7         128.27   Shr

Po2              Desg FWD 9         128.28   Shr

Switch1#

---------------------------------------------------

Thanks a lot in advance.

Regards,
Chandu       

[JohnTylerPearce]

Can you post your config for all Etherchannel configurations for the etherchannel going to Switch3 from Switch2? Also, are these ports all the same speed?

[chandra_rc16]

I posted it already right, what do you want me to post from swtich1 ? Please tell me command.

Thanks in advance.

Regards,
Chandu

[chandra_rc16]

The only etherchannel configured on Switch2 is for Switch1. There is no etherchannel from Switch2 directly connected to Switch3.

Regards,
Chandu

[acampbell]

Chandu,

Looks to me like you have the wrong ether channel group number int

switch 1 ports f0/5 & fas 0/6 they should be in group 2 not 1

try

!

int range fas0/5 - 6

channel-group 2 mode desirable

!

Regards,
Alex.
Please rate useful posts.

[chandra_rc16]

Hi Alex,

------

Looks to me like you have the wrong ether channel group number int

switch 1 ports f0/5 & fas 0/6 they should be in group 2 not 1

------

On Switch3, i configured two channels for redundancy purpose, if 1st goes down, then second one should come up.

1      Po1(SD)           PAgP   Fa0/5(I) Fa0/6(I)

2      Po2(SU)           PAgP   Fa0/3(P) Fa0/4(P)

So, i should configure the same setup in Switch1, right? That's what i did.

1      Po1(SU)           PAgP  Fa0/1(P) Fa0/2(P) Fa0/5(I) Fa0/6(I)

2      Po2(SU)           PAgP   Fa0/3(P) Fa0/4(P)

On Switch1 the ports Fa0/1,Fa0/2 go to the etherchannel for Switch2.

Now i should replicate the etherchannel configuration of Switch3 on Swithc1 to have two Echannels b/w Sw1 and Sw3.

So on Switch1 i configured the Fa0/5,Fa0/6 ports to be in Po1 & the ports Fa0/3,Fa0/4 to be in Po2. But the spanning-tree output on Switch1 is showing the Fa0/5,Fa0/6 whereas it has to show only Fa0/10(PC),Po1,Po2.

Switch1#show spanning-tree

VLAN0001

  Spanning tree enabled protocol ieee

  Root ID    Priority    32769

             Address     0001.9713.EEAD

             This bridge is the root

             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)

             Address     0001.9713.EEAD

             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

             Aging Time  20

Interface        Role Sts Cost      Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/6            Desg FWD 19        128.6    P2p

Fa0/5            Desg FWD 19        128.5    P2p    // These two should be in Po1

Fa0/10           Desg FWD 19        128.10   P2p

Po1              Desg FWD 9         128.27   Shr

Po2              Desg FWD 9         128.28   Shr

The output on SW3 shows below:

Fa0/5            Altn BLK 19        128.5    P2p

Fa0/6            Altn BLK 19        128.6    P2p

Why the channel is not forming?

Regards,
Chandu

[glen.grant]

According to your info you on Sw1you have  1,2,5,6 as a port channel going to sw3 . On Sw 3 you have no port channels with 4 members in it (only shows 5 and 6 ) so you have a mismatch.  You have something wrong on Sw3 either with the connections or the actual port channel config . Looks like 1,2 are not even in the port channel on Sw3 . Look at your config on Sw 1 and match it exactly on Sw 3 .   SW3 should also show 1,2,5,6 in the port channel .  On all use channel-group 1 mode desirable non-silent"  , then shut and no shut the port channel.

[chandra_rc16]

---

According to your info you on Sw1you have  1,2,5,6 as a port channel  going to sw3 .

----

No 3,4,5,6 go to SW3.

---

On Sw 3 you have no port channels with 4 members in it  (only shows 5 and 6 ) so you have a mismatch. 

----

On Sw3 i configured two etherchannels with 2 members.

Switch3#show etherchannel sum

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: 2

Number of aggregators:           2

Group  Port-channel  Protocol    Ports

------+-------------+-----------+----------------------------------------------

1      Po1(SD)           PAgP   Fa0/5(I) Fa0/6(I)

2      Po2(SU)           PAgP   Fa0/3(P) Fa0/4(P)

------------------------------------------------------------------------------------

Regards,
Chandu

[chandra_rc16]

To bang on to point:

Can a Switch whose fours of its interfaces are aggreated into an etherchannel connect to two other switches, using two of its ports from the etherchannel to one switch and other two ports to another switch?

All the inputs are thankful.

Regards,
Chandu

[chandra_rc16]

Please put your inputs, this is not  yet resolved.

Regards,
Chandu

[kcnajaf]

Hi Chandra,

To answer your last question you can not have single etherchannel bundle connected from down stream switch to multiple upstream switches. 

Multi chasis etherchannel (etherchannel from one downstream switch to multiple upstream switches) is supported in three cases

1) Nexus devices with vPC concept.

2) 6500 switches using VSS

3) 3750 switches with stack

Hope that helps.

Regards

Najaf

Please rate when applicable or helpful !!!

[chandra_rc16]

Thank you.

And what does these two lines mean.

Port-channels: 1 Max Portchannels = 1

          //What does this line mean? I really didn't understood this line.

Number of aggregators:           2    

        // Is this the total number of channels on the switch?

Regards,
Chandu

[chandra_rc16]

Need inputs on the above quesstion

Thanks in advance.

Regards,
Chandu

[kcnajaf]

Hi Chandra,

Sorry for the delay in response. Note sure what you are seeing there is correct. I hope this output is from packet tracer. Ideally Max Port Channel should tell us what us the maximum number of port channel supported by that platform. If I remember it right this should have been displayed as 16 on a 2960. If you have a real switch you can check that on the same. Unfortunately I don't have access to any 2960.

For second question your assumption is correct.

Hope that helps.

Regards
Najaf

Sent from Cisco Technical Support iPad App