VLAN question

Unanswered Question
Jun 21st, 2007

I have two servers, 10.1.1.21 and 10.1.1.24/24, both are connected to L2 6500 switches on the same vlan, and the interface VLAN is defined on a router connected to the 6500 switch (VLAN IP is 10.1.1.100/24), when these two servers talk with each other they do so via L2, and traffic between them won?t hit the router, I have a requirement to isolate both vlan at L2 and make them talk via L3, i.e. traffic from 10.1.1.21 should go to the router and then the router should forward it to 10.1.1.24 and vice versa. I can do whatever changes at the router and the switch level, but can not do any changes to the servers IP?s. Any ideas?

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cnuvo Thu, 06/21/2007 - 06:08

I thought about that but was not sure when 10.1.1.21 tries to send a packet to 10.1.1.24, it usualy uses ARP to get the MAC address of 10.1.1.24, when configuring the PVLAN, who is going to respond to the ARP request? How will the packet travel from server 21 to 24?

Edison Ortiz Thu, 06/21/2007 - 06:18

Your default gateway will be configured as promiscuous port while your servers will be configured as isolated ports.

All packets sourcing to/from isolated ports can only go to promiscuous ports. Isolated ports are in total isolation, it's like having those 2 devices in total separate VLANs.

abdel_n Thu, 06/21/2007 - 06:13

The solution is PVLAN (private VLAN?s), it?s implemented differently depending on the switch platform. On catalyst 2950/3550 it?s named (protected ports).

This is a brief explanation of PVLAN on C6500 platform

PVLAN?s allow you to protect hosts in the same vlan from each other by assigning switch ports to different types:

- Isolated: ports communicates only with promiscuous ports.

- Promiscuous: Communicates with all ports, generally default gateways of segments are promiscuous, common servers to all isolated and community ports and load-balancer between servers in isolated or communities.

- Community: communicate with other members of the same community and all promiscuous.

Those PVLAN ports are associated with a set of supporting VLANs:

- Primary VLAN: carries traffic from promiscuous ports to isolated, community and other promiscuous ports.

- Isolated VLAN (secondary VLAN) : carries traffic from isolated ports to promiscuous ports.

- Community VLAN(secondary VLAN): carries traffic between community ports and promiscuous ports.

In your case:

- servers .21 and .24 will belong to a separated vlan X, and set the vlan to a isolated (secondary PVLAN).

- The port connecting you gateway router will belong to a separated vlan Y, and set the vlan to primary PVLAN

Here is a link for more thorough explanation about PVLAN on C6500 12.2SX:

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_guide_chapter09186a0080160a44.html

Good work!

Abdel

cnuvo Thu, 06/21/2007 - 06:17

I think there's misundertanding here, I need to isolate the two servers .21 and .24 from each other at L2..

Edison Ortiz Thu, 06/21/2007 - 06:19

That's what Private VLANs will provide. Please read the links and understand its concept !

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