From: simon hart (simon@harttel.com)
Date: Fri Sep 02 2005 - 16:36:58 GMT-3
All,
This may be a dumb question but has got me a little confused when
configuring ports on a 3550.
I have the following setup
R3 e0/0-------------------fa0/3 Cat 3550
R3 is connected to the Cat on Fa0/3. Fa0/3 is configured as follows:
interface FastEthernet0/3
switchport access vlan 363
switchport mode dynamic desirable
R3 int e0/0 is configure as
interface Ethernet0
ip address 192.10.1.3 255.255.255.0
If I look at the spanning tree for vlan 363 on the cat, I will see the
following:
Interface Port ID Designated Port
ID
Name Prio.Nbr Cost Sts Cost Bridge ID
Prio.Nbr
---------------- -------- --------- --- --------- -------------------- -----
--- Fa0/6 128.6 19 FWD 109 33131 000e.381f.d100 128.6 Fa0/24 128.24 100 FWD 109 33131 000e.381f.d100 128.24 Po1 128.65 9 FWD 100 33131 0009.e8b9.c200 128.65Now whilst working on a DLSW problem, I put R3's int e0 into bridge-group 1 (running ieee). After applying the configuration, I lose connectivity on the switch. The spanning tree on the CAT looks like below:
Interface Port ID Designated Port ID Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr ---------------- -------- --------- --- --------- -------------------- ----- --- Fa0/3 128.3 100 BLK 0 33131 0009.e8b9.c200 128.3 Fa0/6 128.6 19 FWD 9 33131 000e.381f.d100 128.6 Fa0/24 128.24 100 FWD 9 33131 000e.381f.d100 128.24 Po1 128.65 9 FWD 0 33131 0009.e8b9.c200 128.65
Also the int Fa0/3 is now trunking:
Port Mode Encapsulation Status Native vlan Fa0/3 desirable n-isl trunking 1
Port Vlans allowed on trunk Fa0/3 1-4094
Port Vlans allowed and active in management domain Fa0/3 1,4-7,32,77,363,777
I know that if I change the int Fa0/3 to switchport mode access the trunking will stop, and the span tree will go back to normal (i.e. no blocking).
My question is how can a trunk form between R3 and the CAT. R3 is a 2500 using a 10Mbps ethernet interface, and thus no trunking capability, however the CAT says that it is trunking. Is this normal behaviour?
Also, when configuring DLSW and putting a bridge statement on an ethernet interface is it a must to change the Cat port to switchport mode access?
Any guidance or comments will be greatly appreciated
Thanks
Simon
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