interface fa1/0/26 connected to a switch, goes in err-disable state even after NO SH.

[rehan alam]

I am cascading one new switch 3750G (int Gi1/0/1) with an existing 3750G (int fa1/0/26) switch.. But the interface fa1/0/26 goes in err-disable state even after NO SH.. also i have diable Spanning treebpdu guard and disable spanning tree portfast. But still the issue is not resolved.

Please help.

[Bilal Nawaz]

Could you kindly post the configs of both ports please.

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[pille1234]

Do a 'show int sta err-dis' once the port is disabled.

[rehan alam]

Please find the configuration

New Switch

int GigabitEthernet1/0/1

switchport trunk encap dot1q

switchport mode trunk

duplex auto

speed auto

snmp trap link-status

  spanning-tree portfast default

spanning-tree bpduguard disable

end

Existing Switch

int FastEthernet1/0/26

switchport trunk encap dot1q

switchport mode trunk

duplex auto

speed auto

snmp trap link-status

spanning-tree portfast default

spanning-tree bpduguard disable

end

[Bilal Nawaz · Accepted solution]

could you please try this please:

New Switch

int GigabitEthernet1/0/1

switchport trunk encap dot1q

switchport mode trunk

speed 100

duplex full

snmp trap link-status

spanning-tree bpduguard disable

end

Existing Switch

int FastEthernet1/0/26

switchport trunk encap dot1q

switchport mode trunk

speed 100

duplex full

snmp trap link-status

spanning-tree bpduguard disable

end

If you want spanning-tree portfast this is an option i think, but i'd rather leave this out for now due to t'shooting this problem:

Switch(config-if)#spanning-tree portfast trunk

%Warning: portfast should only be enabled on ports connected to a single

host. Connecting hubs, concentrators, switches, bridges, etc... to this

interface  when portfast is enabled, can cause temporary bridging loops.

Use with CAUTION

Switch(config-if)#

But as the message says, please use this with caution. Show interface would be useful... and show interface status err

There are various reasons for the interface to go into errdisable. The reason can be:

• Duplex mismatch
• Port channel misconfiguration
• BPDU guard violation
• UniDirectional Link Detection (UDLD) condition
• Late-collision detection
• Link-flap detection
• Security violation
• Port Aggregation Protocol (PAgP) flap
• Layer 2 Tunneling Protocol (L2TP) guard
• DHCP snooping rate-limit
• Incorrect GBIC / Small Form-Factor Pluggable (SFP) module or cable
• Address Resolution Protocol (ARP) inspection
• Inline power

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00806cd87b.shtml

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[rehan alam]

Its done now.. thanks for the help Bilal.

its showing connected now..can ping the new switch IP. But new switch is not authenticating with Tacacs .. working to resolve the same.

[Bilal Nawaz]

Make sure your new switch management IP is in ACS as an AAA device?

and that all config is in place to cater for tacacs+

You're welcome!

Please rate useful posts and remember to mark any solved questions as answered. Thank you.