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Cisco Employee

is it true that spanning tree loop never occur if all links are using port channel?

is it true that spanning tree loop never occur if all links are using port channel?

if it is true, does it mean that no need to apply loop guard and root guard for all port channels?

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VIP Mentor

is it true that spanning tree

is it true that spanning tree loop never occur if all links are using port channel? no

You can still use loopguard on an etherchannel you need to be aware as an example in pvst if you get unidirectional failure it make the po inconsistent and down for all links for that particular vlan when the issue occurs, so if link 1 fails out of 4 links then the 4 links become down state for that vlan for stp but it will still operate for other vlans and not physically shut the po

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Cisco Employee

juniper engineer told me that

juniper engineer told me that all links are port channel from juniper with cisco switch,

so spanning tree loop impossible to occur, master and backup juniper switch are all port channels, and to cisco switch are all port channel too

i am thinking whether this is only true in mixed juniper and cisco topology but not in topology if all cisco switch, is it true?

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VIP Mentor

I think what he meant was

I think what he meant was when 2 switches have multiple links together between the switches yes you can easily cause a loop if stp is not in place as traffic will loop around at layer 2

if you bundle all the links together there is only 1 path like having 1 physical link between the 2 switches so there cant really be a loop , that would only be the case though if there were ONLY 2 switches directly connected to each other by port-channels , doesn't matter whether cisco or juniper stp is a feature available on multiple platforms and works the same way generally on each as its a link loop avoidance feature

if you had multiple switches same broadcast domain with multiple port channels a loop could still form if not planned correctly at stp

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Cisco Employee

in our case, they said our

in our case, they said our case is to not separate vlans into different STP, 

mixed with cisco switch, it can not use MSTP, it need RSTP

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VIP Expert

MSTP is a "better" variant of

MSTP is a "better" variant of RSTP.

Juniper supports RSTP, but again, (I recall) they don't support per VLAN RSTP.

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Cisco Employee

they said that MSTP approach

they said that MSTP approach is not feasible if connecting with juniper

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Cisco Employee

if distribution layer switch

if distribution layer switch is juniper , access switch is cisco

is it true that cisco switch not need to configure loop guard at etherchannel which are root port ?

if distribution layer switch is cisco , access switch is juniper

is it true that cisco switch not need to configure root guard at etherchannel which trunk to juniper?

are loop guard and root guard for single link and one port only?

i had experience in creating a loop at distribution layer when connect a switch to access switch which had not configured root guard at trunk port

i remembered that the distribution layer using etherchannel too

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VIP Mentor

they said that MSTP approach

they said that MSTP approach is not feasible if connecting with juniper

MSTP should works between cisco and juniper switches its on there ex series switches

makes no difference whether its juniper or Cisco you need to just look at the feature and plan out stp correctly based on your network not its vendor type  , Root guard is best deployed towards ports that connect to switches which should not be the root bridge

is it true that cisco switch not need to configure root guard at etherchannel which trunk to juniper?

root guard and loop guard are optional commands you don't have to use them but you can if you want to

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VIP Expert

Who are "they"?

Who are "they"?

What are the actual devices?

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Cisco Employee

it seems that loop guard

it seems that loop guard should not enable in port channel because it will block the whole logical link

if loop guard should not enable in port channel, 

then can it imply loop never occur in port channel?

if distribution layer switch is juniper , access switch is cisco

is it true that cisco switch not need to configure loop guard at etherchannel which are root port ?

if distribution layer switch is cisco , access switch is juniper

is it true that cisco switch not need to configure root guard at etherchannel which trunk to juniper?

Highlighted
Cisco Employee

all trunk port using port

all trunk port using port channels, one port channel is connected with backup switch

another port channel is connected with cisco switch

it seems that loop guard should not enable in port channel because it will block the whole logical link

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VIP Expert

No, STP and port-channel

No, STP and port-channel needs don't differ between Cisco and Juniper, either on only their equipment or between the two vendors.

However, Cisco supports PVSTP and Juniper doesn't, so mixing them, at L2, is a bit of fun.  Both, though, should support MST.

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VIP Mentor

Hi

Hi

I think a proper STP configuration is always required to avoid layer 2 loops, independent if you are using port channel or not, please check this link:

https://supportforums.cisco.com/discussion/11059606/how-does-loop-form-misconfigured-etherchannel

Hope it is useful

:-)




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VIP Advisor

I cant see how that could be

I cant see how that could be the case,

unless all physical ports on a switch form a port channel to a single remote switch.  Port channels still run STP but pretty much leave the physical port that constitute a single port channel out of the equation. meaning only the port channel is calculated as a single STP port (the cost can vary based on how many physical ports are in the same port channel)

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