vlans on cisco 2851 Gig ethernet

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Feb 25th, 2009

Hi

can i configure the 2 Gig ethernet ports on cisco 2851 as part of diffrent vlans and assign ip addresses to that vlans.attahced diagram for the reference.

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naveen_b81 Wed, 02/25/2009 - 23:42

I think the default port in cisco 2851 are routed ports and cannot perform switching. You can directly assign IP address to the two ports and connect them to the switchports in respective VLAN's.

Cheers,

Naveen

sameermunj Thu, 02/26/2009 - 00:18

Hi

Both ports should be in same subnet and should be part of all 4 vlans so if i enable dot1 q on that port i need to create 4 subinterfaces each on both the ports and assign ip addesses..somehow i want to bundle those 2 gig ports.

Paolo Bevilacqua Thu, 02/26/2009 - 01:16

You can use an IRB configuration to have both ports in the same subnet, that is, the same bridge group and configure L3 on the BVI interface.

However, one interface will block due to spanning-tree, and you will find that it's very unlikely that you ever experience faults in the connected switches, so actually there is much true redundancy to gain, at the cost of a more complicated configuration.

sameermunj Thu, 02/26/2009 - 01:30

Hi

so with IRB i will have 4 subinterafces on both gig ports corrosponding to 4 vlands and all 4 subinterfaces will be part of diffrent bridge group on both the gig port.so the configuration will look like

interface Gig 0/0

no ip address

!

interface Gig 0/0.1

encapsulation dot1Q 10

bridge-group 10

!

interface Gig 0/0.2

encapsulation dot1Q 20

bridge-group 20

interface Gig 0/0.3

encapsulation dot1Q 30

bridge-group 30

!

interface Gig 0/0.4

encapsulation dot1Q 40

bridge-group 40

interface Gig 0/1

no ip address

!

interface Gig 0/1.1

encapsulation dot1Q 10

bridge-group 10

!

interface Gig 0/1.2

encapsulation dot1Q 20

bridge-group 20

interface Gig 0/1.3

encapsulation dot1Q 30

bridge-group 30

!

interface Gig 0/1.4

encapsulation dot1Q 40

bridge-group 40

interface BVI 10

ip address 192.168.10.1/24

interface BVI 20

ip address 192.168.20.1/24

interface BVI 10

ip address 192.168.30.1/24

interface BVI 10

ip address 192.168.40.1/24

also it would be great if u can share with me the other solution which u feel complicated.

Paolo Bevilacqua Thu, 02/26/2009 - 01:38

Also configure "bridge irb" and "bridge 10 route ip".

http://www.cisco.com/en/US/tech/tk389/tk815/technologies_tech_note09186a0080094663.shtml

Remember that only one port will be active at all times, so there is no bandwidth to gain.

If you're connecting to a single switch, you can use etherchannel instead, but consider that ISR routers do not have performances enough to fill one gigabit, so in that case too, it is not really worth it.

sameermunj Thu, 02/26/2009 - 02:08

Hi

i am connecting 2 diffrent switches so no chance to configure ether channel.

i dont mind 1 port in blocking mode as its 1 G port.

so in shorft i can have subinterfaces of the main interaface as part of diffrent brigde group.

u were talking about some other complicated configuration in previous mail.u have not highlited the same further.

Paolo Bevilacqua Thu, 02/26/2009 - 03:01

I meant the IRB config that is complicated and in many cases not necessary. If you have L3 switches configure inter-vlan routing there.

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