Layer 3 SW and untagged packets

[Rainer Blaes]

Dear all,

pls see here our setup:

Configuration:
- - Catalyst 3750
- - multiple ports configured in Trunk mode running multiple VLANs
- - single 'normal' port receives untagged IP packets

Question:
how to make the Layer 3 switch to put the untagged IP packets on the
VLANs covering the target IP address ?

Example:

VLANs running on the trunk ports:
[VLAN-1] : 192.168.1.*
[VLAN-2] : 192.168.2.*
[VLAN-3] : 192.168.3.*

One IP packet is received on 'normal' port with target address
192.168.2.34. Is the packet automatically tagged with and put on
'VLAN-2' ?

Another IP packet is received on 'normal' port with target address
192.168.3.34. Is the packet automatically tagged with and put on
'VLAN-3' ?

Many thanks in advance for any hint!

Rainer

[srikanth ath]

Hello,

Hope this answers you

PC1 (10.10.10.1)--SW1--Native VLAN 10 <<<>>Native VLAN 20---SW2--PC(10.10.10.2)

PC1 - In VLAN 10

PC2 - In VLAN 20

The packet comes to SW1, SW 1 send this frame accross trunk without any tag since on SW1 native vlan is 10. On next SW 2 the frame is received. Since frame that's received not have any vlan tag so it assumes it is meant for its local native vlan so it through the frame into vlan 20.

Congrats PC 1 pings PC2 though in different vlan.

In addition please follow below link for deail explanation:

http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/configuration/guide/cli/AccessTrunk.pdf

http://docs.oracle.com/cd/E27300_01/E27309/html/vmusg-network-vlans.html

Please rate the helpful posts

Regards,

srikanth

[Rainer Blaes]

Dear srikanth!

Sorry, my answer is not yet answered. I try to describe the problem in more detail.

Please refer to attached drawing too.  The firewall sends untagged packets to a por

t of the Catalyst L3 switch (the port acts as a router and has got the IP address 192.168.0.2).

The switch has got other ports configured as trunk ports, on which several VLANs are run

(here VLAN-1 .. VLAN-3).  Q: how can I configure the switch to - - tag the incoming untagged

packets with the right VLAN-ID (here: packet destined for 192.168.1.15 with VLAN-ID=

1, 192.168.2.15 with VLAN-ID=2 and 192.168.3.15 with VLAN-ID=3) - - put the packets on

the right VLAN  It could be that this is automatically done by the Cisco IOS but I have not

found a statement indicating that.

Thanks for your help, Rainer

[cadet alain]

Hi,

so the port between firewall and switch is a L3 routed port and you've got the corresponding SVIs on the switch for the respective destination VLANs. So the switch will simply do routing and send it out the corresponding SVI and then rewrite the L2 header and as it passes a trunk port the L2 process will take care of the tagging.

So don't worry this will be automatically done for you.

Regards.

Alain

Don't forget to rate helpful posts.

[NicolasDelannoy7248]

Hi,

I had the exact same behavior this morning with a pretty new config, and I realized that "ip routing" was not set. If it can help someone