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L3 equipment spanning tree or looping

KDG_dhkd
Level 1
Level 1

hello, everyone


I have a question regarding spanning trees.

 

 

 

11.jpg

The 6500 chassis are all routed ports.

L2 is all switch ports.


1. It consists of full mesh at this time, but can spanning trees occur? or looping ?

 

2. And when the port where L2 and 6500 chassis are connected is a routed port,
Can looping occur when L2 equipment is a switch port except for the port connected to the 6500 chassis?

1 Accepted Solution

Accepted Solutions

Giuseppe Larosa
Hall of Fame
Hall of Fame

Hello @KDG_dhkd ,

STP is a protocol that prevents bridging loops.

Issues can arise if STP is disabled or in some special cases but usually STP works well.

 

if all links to / from Cat6500 are routed ports the only L2 link is the link between the two switches.

 

if a routed port connects to a L2 switchport the routed port will speak with the SVI associated to the VLAN the L2 port belongs to.

There is no risk of loop in this case as each C6500 is a routed port.

 

Hope to help

Giuseppe

 

View solution in original post

7 Replies 7

balaji.bandi
Hall of Fame
Hall of Fame

If the mesh networks is Layer 3 configure, ther eis no Loops.

 

if they are Layer 2, you see Looops and STP Blocks it.

 

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Thank you for your time.

Giuseppe Larosa
Hall of Fame
Hall of Fame

Hello @KDG_dhkd ,

STP is a protocol that prevents bridging loops.

Issues can arise if STP is disabled or in some special cases but usually STP works well.

 

if all links to / from Cat6500 are routed ports the only L2 link is the link between the two switches.

 

if a routed port connects to a L2 switchport the routed port will speak with the SVI associated to the VLAN the L2 port belongs to.

There is no risk of loop in this case as each C6500 is a routed port.

 

Hope to help

Giuseppe

 

Thank you for your time.

the problem is solved.

Joseph W. Doherty
Hall of Fame
Hall of Fame

For there to be a L2 loop, you need the "same" L2 domain to transit across ports and (generally) devices.  Basically, you need to determine if a L2 frame can, somehow, transit some full loop, within your topology.  If it cannot, a loop cannot form.  If it can, you need something like STP to (logically) break a link somewhere within the loop.  (BTW, on VLAN capable switches, STP might be used for all VLANs [common with many network vendors] or per-VLAN [generally what Cisco switches support].)

So, for example, you mention, "L2 is all switch ports.", but on a VLAN capable switch, are they the same L2 domain?  (BTW, it's possible to interconnect switches using different VLANs on ports.  Logically a L2 domain is a "shared/common wire".)

Routed interfaces are L3, and as such, they "break" L2 paths.  I.e. they create different "shared/common wire" segments.  (NB: normally, loops in L3 topologies are fine, although you can have "looping" within a L3 network.  The latter, generally, is caused by the topology's routers not all having the same "view" of the topology.)

Thank you for your time.

 

the problem is solved.

..

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