Connecting Nexus 7k and 3750 switch on multiple access port interfaces

[sreeraj.murali]

Hi,

With respect to below topology, between Nexus7k and Cisco3750 switch, If all the interface eth1/14,1/15,1/16,2/15 are configured in acces mode and same access vlan, Will it cause a loop ? and what about, if all the interfaces configured with different access vlan? Please advice.

################Nexus7k############

     |                   |                     |                  |

  Eth1/14       Eth1/15         Eth 1/16      Eth 2/15

     |                   |                     |                  |

 ###############3750Sw#############

Thanks

Sreeraj

[Reza Sharifi]

Hi,

You should put all interfaces in a Portchannel, so they logically look like one interface, if not STP will block 3 out of 4 interfaces.

HTH

[sreeraj.murali]

Thanks, we cannot put in port channel considering securing different service with separate vlans. Will my topology work(with all interface in forwarding), if all interfaces are in placed in different Customer vlans?

[Reza Sharifi]

When you connect multiple switches via redundant physical links, to prevent loop STP will allow one port to be in forwarding mode and the rest in blocking. Also, not using Portchannel (separate links) does not provide any security because everything is still connected to the same 2 switches.  If you want to separate customers, you may want to look at VRF.

HTH 

[sreeraj.murali]

Hi,

I am pasting the show cdp neighbors command from Nexus7k, currently in the network the Nexus 7k is connected to 3750 switch, the way, i mentioned previously. Please help, how this connectivity is working then,all in forwarding state. Please let me know, for any other output.

LINY-N77K01-PROD# show cdp neighbors
Capability Codes: R - Router, T - Trans-Bridge, B - Source-Route-Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater,
                  V - VoIP-Phone, D - Remotely-Managed-Device,
                  s - Supports-STP-Dispute

Device-ID          Local Intrfce  Hldtme Capability  Platform      Port ID
LINY-3750-01M.highstreetit.com
                    mgmt0          147    R S I     WS-C3750G-24T Gig1/0/5
usny01ethr002.hitscs.local.hitscs.local(FOX1829GY21)
                    Eth1/9         140    S I s     N5K-C5596UP   Eth1/9
usny01ethr001.hitscs.local.hitscs.local(FOX1750GLYE)
                    Eth1/10        172    S I s     N5K-C5596UP   Eth1/10
usny01ethr003.hitscs.local.hitscs.local(FOC1737R05G)
                    Eth1/11        163    R S I s   N3K-C3048TP-1 Eth1/38
usny01ethr003.hitscs.local.hitscs.local(FOC1737R05G)
                    Eth1/12        164    R S I s   N3K-C3048TP-1 Eth1/37
LINY-3750-01M.highstreetit.com
                    Eth1/14        138    R S I     WS-C3750G-24T Gig2/0/12
LINY-3750-01M.highstreetit.com
                    Eth1/15        147    R S I     WS-C3750G-24T Gig1/0/12
LINY-3750-01M.highstreetit.com
                    Eth1/16        147    R S I     WS-C3750G-24T Gig1/0/13
usny01ethr001.hitscs.local.hitscs.local(FOX1750GLYE)
                    Eth2/9         172    S I s     N5K-C5596UP   Eth1/9
usny01ethr002.hitscs.local.hitscs.local(FOX1829GY21)
                    Eth2/10        140    S I s     N5K-C5596UP   Eth1/10
usny01ethr004.hitscs.local.hitscs.local(FOC1737R05M)
                    Eth2/11        165    R S I s   N3K-C3048TP-1 Eth1/38
usny01ethr004.hitscs.local.hitscs.local(FOC1737R05M)
                    Eth2/12        165    R S I s   N3K-C3048TP-1 Eth1/37
LINY-3750-01M.highstreetit.com
                    Eth2/15        147    R S I     WS-C3750G-24T Gig1/0/10
DECO-N77K01-PROD(FXS1836Q2BB)
                    Eth2/24        158    R S s     N77-C7706     Eth2/24

Please find the show spanning tree output from 7k

LINY-N77K01-PROD# show spanning-tree interface ethernet 1/15 detail

 Port 143 (Ethernet1/15) of VLAN1004 is designated forwarding
   Port path cost 4, Port priority 128, Port Identifier 128.143
   Designated root has priority 25580, address 002a.6a5c.95c2
   Designated bridge has priority 25580, address 002a.6a5c.95c2
   Designated port id is 128.143, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 4
   Link type is point-to-point by default
   BPDU: sent 26861601, received 123794

LINY-N77K01-PROD# show spanning-tree interface ethernet 1/14 detail

 Port 142 (Ethernet1/14) of VLAN0903 is designated forwarding
   Port path cost 4, Port priority 128, Port Identifier 128.142
   Designated root has priority 25479, address 002a.6a5c.95c2
   Designated bridge has priority 25479, address 002a.6a5c.95c2
   Designated port id is 128.142, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 869237, received 51

LINY-N77K01-PROD# show spanning-tree interface ethernet 1/16 detail

 Port 144 (Ethernet1/16) of VLAN0136 is designated forwarding
   Port path cost 4, Port priority 128, Port Identifier 128.144
   Designated root has priority 24712, address 002a.6a5c.95c2
   Designated bridge has priority 24712, address 002a.6a5c.95c2
   Designated port id is 128.144, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 26986166, received 19

LINY-N77K01-PROD# show spanning-tree interface ethernet 2/15 detail

 Port 271 (Ethernet2/15) of VLAN1004 is designated forwarding
   Port path cost 4, Port priority 128, Port Identifier 128.271
   Designated root has priority 25580, address 002a.6a5c.95c2
   Designated bridge has priority 25580, address 002a.6a5c.95c2
   Designated port id is 128.271, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 6
   Link type is point-to-point by default
   BPDU: sent 26986181, received 123752

Thanks

Sreeraj

[sreeraj.murali]

Hi Experts,

Can some one help please ?

Thanks & Regards

Sreeraj