Query related to a stp and vlan case

Essentially NOTHING will work in this network, as far as I can tell.

It doesn't matter whether the VLANs are statically configured by switch port, or whether all of the ports are 802.1Q VLAN-aware. You have no trunk links between the three switches, and none of these switches is configured as a router, so it looks to me like nothing will communicate.

Think about what a switch would do with a frame arriving at one port, configured to only accept VLAN X frames, when none of its other ports are members of that VLAN X. The frame will get dropped on the floor.

The link between switch 1 and switch 2, and between switch 2 and switch 3 (or switch 1 and switch 3), have to be configured as trunks. Then you can at least get frames between all the switches.

If these segments are configured as trunks, and without any router function in the net, the three PCs off switch 2 will still NOT be able to communicate among each other, because they each belong to different VLANs.

If you make even those PC links trunk segments, and the PCs themselves VLAN-aware, then you can allow each PC to intercommunicate at Layer 2 by becoming member of the same VLAN as the other PCs, or you can add an IP layer and configure the PCs as routers. In this last case, each PC could belong to a different VLAN, and still intercommunicate, using IP routing to jump between different VLANs.

Bert

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Hello

What u say about inter-vlan communication is it possible ..... if yes plz tell how ????

Thanks

Vikrant

A VLAN is a *virtual LAN*, i.e., distinct VLANs appear to be physically separate Local Area Networks. As with all separate networks, communication among them can be effected by using a router.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

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It might help vicky (or not) to hear that inter-VLAN routers usually are purely software based, often with only a single hardware interface (ethercard).

VLANs share physical media with other traffic but the packets are at least tagged (often by port number) and usually encrypted to prevent traffic mixing on a logical level.

A computer (routers are computers) listens to the traffic from both VLANs (crypto CPU loads can be significant) and decides which packets to translate from one VLAN onto another.

-- Robert

I gather that you are referring to some kind of app to app level encryption? I'm not -aware- of any switch / router that does encryption at the point where an untagged VLAN enters the network, and decryption at the point where the untagged VLAN exits the network (possibly a number of hops away), all transparently to the hosts. Or rather, to the extent that I have heard of such things, I would probably call them Virtual Private Networks (VPNs) rather than encrypted VLANs -- especially as VPNs can carry VLAN-tagged packets within them.

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And is inter- port based vlan communication is possible in l 2 switch or for this the switch controller register support is required

Thanks

Vikrant

Walter Roberson wrote in part:

Correct. I was not referring to 802.1Q tagging (layer 2) but rather more to plain vanilla IP (layer 3) which is probably best described as VPN.

-- Robert

Please read my original response. Communications among VLANs (indeed, among *any* LANs) can be accomplished using a router. I am sorry if you do not understand this, or if this is not the answer you want.

I have no idea what a "switch controller register" *is*, much less whether it may be required for inter-port based VLAN communication.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

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Hello Sir

I ve a query related to inter-vlan(port based) communication so first please read my query which in my share web file named as

stp and vlan case.txt

the link for my share web file is --

please read it and then please reply.

Thanks

Vikrant

I read your file, and my answer is unchanged. You seem to believe that, because there are multiple ports physically connected to a single switch, that the switch *MUST* provide the mechanism for communicating among all of those ports. However, if you configure some of the switch ports to be in disjoint VLANs (as you have), then it is possible-- indeed, likely--that the switch will NOT provide such communication. By configuring separate VLANs as you have shown, you are, in essence, telling the switch NOT to allow communication directly among those VLANs.

As I have said many times now, communications among VLANs can be accomplished using a router. In the diagram you have provided, you show no router, so there will be no communications among the separate VLANs. If you want communications among all of the ports, then don't configure them into separate VLANs.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

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Hello Sir

I 've a stp_and_vlan.jpg file in my web file sharing

this wat i m asking is same of port vlan group query but please visit in my file

Thanks

VIkrant

I looked at this file, and the statements in it, but I really do not understand what the question is, perhaps because of a language problem. I will try to explain what I *do* see.

You have a switch (S3) with 8 ports, organized as seven distinct port-based VLANs. Looking at this switch *alone*, I can tell you that there will be no user frames forwarded between any ports other than ports 4 and 5, since only those two ports are in the same VLAN (VLAN 4). This behavior is completely independent from, and has nothing to do with the fact that some ports are designated and one is a root port. Spanning Tree connectivity is generally unrelated to the issue of frame forwarding within a VLAN.

Is there some other question here that I am not seeing?

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com