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Problems trunking 3548/2950?

I am having trouble trunking these two switches together. I am running a Here is the following information that I am seeing:

I have a foundry router trunking to the gig port on a 3548. I am announcing the 10.5.0.1/29 off of the virtual interface 7. I have set the mgnt vlan (int vlan 7 )10.5.0.2/29, and can ping across to gateway...but I can't get the 3548 to trunk with the 2950 (10.5.0.3)? I don't know if looking at the sh int * switchport is telling me something or not. On the 3548, I see the following "Access Mode VLAN: 0 ((Inactive))", and on the 2950 I see this, "Access Mode VLAN: 1 (default)." I keep getting incomplete arp entries, and can't ping across. I have tried to the "switchport nonegotiate" on the 2950 as well, and this didn't change anything. I have changed both switches native vlan from 1 to 1000, and have moved the mgnt vlan from 1 and 7 as well.Then I tried to trunk two 2950s...same config on both and no luck, until I enable the "switchport nonegotiate" command on both switch ports. Any ideas of what I may be doing wrong.

gig3-3548#sh arp

Protocol Address Age (min) Hardware Addr Type Interface

Internet 10.5.0.3 0 Incomplete ARPA

Internet 10.5.0.2 - 0007.8502.c740 ARPA VLAN7

Internet 10.5.0.1 95 0004.8048.7500 ARPA VLAN7

interface FastEthernet0/1

duplex full

speed 100

switchport trunk encapsulation dot1q

switchport mode trunk

no cdp enable

!

gig3-3548#sh int fa0/1 switchport

Name: Fa0/1

Switchport: Enabled

Administrative mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: Disabled

Access Mode VLAN: 0 ((Inactive))

Trunking Native Mode VLAN: 1 (VLAN1)

Trunking VLANs Enabled: ALL

Trunking VLANs Active: 1,7,1000

Pruning VLANs Enabled: 2-1001

Priority for untagged frames: 0

Override vlan tag priority: FALSE

Voice VLAN: none

Appliance trust: none

gig3-3548#sh vlan

VLAN Name Status Ports

---- -------------------------------- --------- -------------------------------

1 default active Fa0/2, Fa0/3, Fa0/4, Fa0/5,

Fa0/6, Fa0/7, Fa0/8, Fa0/9,

Fa0/10, Fa0/11, Fa0/12, Fa0/13,

Fa0/14, Fa0/15, Fa0/16, Fa0/17,

Fa0/18, Fa0/19, Fa0/20, Fa0/21,

Fa0/22, Fa0/23, Fa0/24, Fa0/25,

Fa0/26, Fa0/27, Fa0/28, Fa0/29,

Fa0/30, Fa0/31, Fa0/32, Fa0/33,

Fa0/34, Fa0/35, Fa0/36, Fa0/37,

Fa0/38, Fa0/39, Fa0/40, Fa0/41,

Fa0/42, Fa0/43, Fa0/44, Fa0/45,

Fa0/46, Fa0/47, Fa0/48, Gi0/2

7 VLAN0007 active

1000 VLAN1000 active

1002 fddi-default active

1003 token-ring-default active

1004 fddinet-default active

1005 trnet-default active

VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2

---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------

1 enet 100001 1500 - - - - - 1002 1003

7 enet 100007 1500 - - - - - 0 0

1000 enet 101000 1500 - - - - - 0 0

1002 fddi 101002 1500 - - - - - 1 1003

1003 tr 101003 1500 1005 0 - - srb 1 1002

1004 fdnet 101004 1500 - - 1 ibm - 0 0

1005 trnet 101005 1500 - - 1 ibm - 0 0

interface FastEthernet0/1

description gig-3548

switchport mode trunk

no ip address

duplex full

speed 100

no cdp enable

agg5-2950#sh int fa0/1 switchport

Name: Fa0/1

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: On

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Protected: false

Voice VLAN: none (Inactive)

Appliance trust: none

agg5-2950#sh vlan

VLAN Name Status Ports

---- -------------------------------- --------- -------------------------------

1 default active Fa0/2, Fa0/3, Fa0/4, Fa0/5

Fa0/6, Fa0/7, Fa0/8, Fa0/9

Fa0/10, Fa0/11, Fa0/12, Fa0/13

Fa0/14, Fa0/15, Fa0/16, Fa0/17

Fa0/18, Fa0/19, Fa0/20, Fa0/21

Fa0/22, Fa0/23, Fa0/24

1002 fddi-default active

1003 token-ring-default active

1004 fddinet-default active

1005 trnet-default active

VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2

---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------

1 enet 100001 1500 - - - - - 0 0

1002 fddi 101002 1500 - - - - - 0 0

1003 tr 101003 1500 - - - - - 0 0

1004 fdnet 101004 1500 - - - ieee - 0 0

1005 trnet 101005 1500 - - - ibm - 0 0

TIA,

D-

1 REPLY

Re: Problems trunking 3548/2950?

Hi,

your problem description is not 100% clear, but I would do following:

1) move mgmt VLAN back to VLAN1 on both switches, enable CDP

2) enable trunk negotiation on both ends (now it's diabled on 3550 and enabled on 2950)

3) check if trunk has come up correctly (Trunking VLANs Active: should list the same VLAN numbers on both trunk sides).

If not: CDP should detect different native VLANs and display an error message to syslog. If trunk negotiation would'n work correctly, I'd try to disable it - but on BOTH line ends).

4) When the trunk is OK then try to move mgmt VLAN to VLAN7 (if it's really necessary, I wouldn't recommend it generally). Finally, disable CDP if you want it disabled.

Regards,

Milan

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