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unable to ping-connect to switch after changing uplink interfaces trunks

nygenxny123
Level 1
Level 1

I have 2 3120 switches..

..dhcp gave one switch an ip

address of 192.168.7.224 the other 7.234 and a default gateway of 192.168.7.1 (vlan1). The switch have 2 uplink connections to the same IDF switch each

Previous to that-all 4 switchports were set as access ports....from idf to new switch..all 4 ports were access for vlan 17

However after I changed 1 port on the new switch and one switch on the IDF swith to trunk mode.I was unable to connect from my pc..wich is on another network...i could only connect from my the IDF switch

VLAN 1 is the default vlan..

I can still connect from the switch that I have not made changes too..

here is the switch that is still working

SW1#sh cdp ne

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID

03 Gig 1/0/25 164 S I WS-C3750G Gig 4/0/16

nyc-wt03 Gig 1/0/23 151 S I WS-C3750G Gig 4/0/8

3-2-4-SW1#sh int trunk

-3-2-4-SW1#

SW1#sh ip route

Default gateway is 192.168.7.1

Host Gateway Last Use Total Uses Interface

ICMP redirect cache is empty

now here is the switch that i cant connect to remotely...only from the IDF uplink it is directly connected to

switch2#sh cdp ne

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID

03 Gig 1/0/25 133 S I WS-C3750G Gig 4/0/15

03 Gig 1/0/23 135 S I WS-C3750G Gig 4/0/17

switch2#sh int trunk

Port Mode Encapsulation Status Native vlan

Gi1/0/23 on 802.1q trunking 1

Gi1/0/25 on 802.1q trunking 1

Port Vlans allowed on trunk

Gi1/0/23 1-4094

Gi1/0/25 1-4094

trunk appears to be fine on the IDF switch

there is no IP address associated in the same subnet on the IDF switch as the new switches..

however im not sure this is an issue since one switch is working fine and the other is not...only after i switched just one port to trunking...

even the secondary link wouldnt provide connectivity

1 Reply 1

Giuseppe Larosa
Hall of Fame
Hall of Fame

Hello Richard,

look for a native vlan mismatch.

use

sh int typex/y switchport

and check the line about Native vlan on both ends.

It is not clear how you could reach the device before, you say your management vlan is vlan1, that the 4 ports were access ports in vlan17.

so you had an alternate path to reach the troubled switch.

You can use shutdown on the IDF switch to disable the new trunk.

after you regain access to the switch check the Native vlan settings.

if one side considers native vlan vlan1 and the other vlan17 untagged frames are associated to different vlans on the two sides of the trunk.

Hope to help

Giuseppe