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7200 vs 7600 VLANs

I am looking for some clarification on support of VLANS. I am looking at an application in which I have a VLAN per home. I want to do Layer 2 forwarding up to a "big" router (7200/7600). I expect to have more than

4096 subscribers (VLANS) per big router. I want the router to do IP forwarding, but NOT to bridge traffic from two homes that happen to have the same VLAN tag.

  1. I heard that the 7600 cannot support more than 4096 VLANS. True?

  2. I heard tha the 7200 CAN support more than 4096 vlans, but will it try to bridge customers with the same VLAN ID? Ovbviously, if two subscribers with the same VLAN ID happen to come in on the same physical port, then the router will assume that they are from the same home.

But suppose I coudl guarantee that if a VLAN ID is reused, it woudl be on a different physical interface. Would things work then?

  1. What are these features called (industry standard terms)? VLAN switching? Port Isolation?

Thanks in advance.

Reply to
zigipha
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You're probably going to have to rethink your network design.

You're also confused a bit by how routers handle VLANs vs. how switches handle VLANs. Maybe picking up a little Cisco router and doing some experiments in a lab setup would be informative to you.

True. Limitation of the standard. The 802.1q frame allocated 12 bits for the VID. I'd like to see how you plan on supporting more than 4096 with only 12 bits.

How would it support more than 4096 with 802.1q standard?

The router won't bridge between VLANs if you don't have bridging turned on, but I don't think you understand how this is all going together yet. A 7206 can have maybe 12 FastE interfaces. How are you bringing all of these into it?

I'm not sure what features you are talking about.

Reply to
Doug McIntyre

If VLANs on the 7600 could be per-port instead of globally on the box, it would be perfectly possible to support more than 4096 VLANs.

VLAN stacking, QinQ or whatever you want to call it. Used in lots of BRAS boxes like for instance the Juniper ERX. A small example from an actual config on one of our boxes:

interface gigabitEthernet 5/0.5510030 svlan id 551 30 ip description "71363" ip unnumbered loopback 46 ! interface gigabitEthernet 5/0.5810011 svlan id 581 11 ip description "71410" ip unnumbered loopback 46

So here you could at least in theory use 4096*4096 VLANs. Your BRAS platform probably has other limitations which means that 16+ million VLANs (customers) is unrealistic in one box. But more than 4096 is absolutely feasible.

Steinar Haug, Nethelp consulting, snipped-for-privacy@nethelp.no

Reply to
Steinar Haug

Doug/Steinar, thank you for your response. I am trying to get up to speed on this and do not have access to a Cisco router to play with. I am not the designer of this network but it is being defined by a customer. I am trying to find out if it is feasible, and any help would be appreciated.

As i understand it, VLANs are used to limit broadcast domains. So, if there are two VLANS being carried on a single GigE port, then the broadcasts on one VLAN will not be seen on the other VLAN.

physical interfaces, then it should bridge the data streams from the two physical ports. So, a broadcast received on VLAN 1 on port A will be switched to VLAN 1 on port B.

Now we get to the router application: if I have two physical ports, can I use the same VLAN on both ports? IF yes, will it treat them as a single subnet or as two distinct subnets. I could see that the router could logicaly extend the number of VLANs supported by using the physical port ID as a way to increase the number of VLANs supported (i.e. 4096 per physical port).

OR..is it a simple fact that, regardless of switch or router, I can only have 4096 distinct outter VLAN tags per switch/router chassis?

Thanks :)

Reply to
zigipha

Agreed, this is standard *switch* behavior. A router, by default, doesn't behave like this at all.

Yes, you can use the same VLAN on both ports, they are treated as two distinct subnets.

Yes, that is one way to increase the total number of VLANs (really, the total number of customers).

Only 4096 distinct outer VLAN tags is a limitation of many *switch* platforms. There is no particular reason to have such a reason for a

*router* platform. The fact that the Cisco 7600 "router" has such a limitation simply shows its switch ancestry.

Steinar Haug, Nethelp consulting, snipped-for-privacy@nethelp.no

Reply to
Steinar Haug

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