Sign in with
Sign up | Sign in
Your question

802.1q vlans trunking

Last response: in Networking
Share
Anonymous
June 13, 2005 6:09:34 AM

Archived from groups: comp.dcom.lans.ethernet (More info?)

Hi,

First sorry for my poor english.

I have to pass packets between 2 switches with vlans. One of these
switches permit to create 256 vlans maximum. I had to configure one
port of this switch in trunk mode in order the two switches could
communicate. I think I had to add the vlans I want to the trunk port.
But can the trunk port transport more than 256 vlans (because of the
limit of 256 vlans of one of the switch)?




Thanks in advance for your reply.
Best regards,


Julien

More about : 802 vlans trunking

Anonymous
June 13, 2005 7:39:58 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

In article <1118653774.646688.119840@g43g2000cwa.googlegroups.com>,
julde <jdelapierre@neuf.fr> wrote:
:I have to pass packets between 2 switches with vlans. One of these
:switches permit to create 256 vlans maximum. I had to configure one
:p ort of this switch in trunk mode in order the two switches could
:communicate. I think I had to add the vlans I want to the trunk port.
:But can the trunk port transport more than 256 vlans (because of the
:limit of 256 vlans of one of the switch)?

The answer will vary with the switch model and software release.

A switch that only allows 256 vlans to be created might have only
256 slots in its per-VLAN MAC address tables, or might only use an
8-bit number internally in storing the information about which MAC is
on which VLAN.

Sometimes, though, it is just a user interface limitation.

I suspect it would be more likely to work if you are in
single spanning-tree mode than in per-VLAN spanning-tree mode.

The "magic numbers" of VLANs that I have heard of in the past include
240, 256, 1000, 1018, 1024, 2000, 4000, and 4096.

It is not uncommon for Cisco switches to support 1024 in "VTP mode"
(which allows dynamic reconfiguration of VLANs from a master machine),
and 4096 in "VTP Transparent mode" -- i.e., the limits can depend on
exactly how the switch is being used.
--
History is a pile of debris -- Laurie Anderson
Anonymous
June 14, 2005 12:10:51 AM

Archived from groups: comp.dcom.lans.ethernet (More info?)

julde wrote:

> I have to pass packets between 2 switches with vlans. One of these
> switches permit to create 256 vlans maximum. I had to configure one
> port of this switch in trunk mode in order the two switches could
> communicate. I think I had to add the vlans I want to the trunk port.
> But can the trunk port transport more than 256 vlans (because of the
> limit of 256 vlans of one of the switch)?

If the switch says it can only handle 256 VLANs, then it most
likely won't be able to transport more than that even on the trunk
link for the simple reason that it won't understand where to
send a packet that it received with a tag for the 257th VLAN.

The switch has to know which ports are members of the VLAN
so that it can limit the propagation of traffic from that
VLAN for frames with an unknown DA, and also must know whether
to transmit the frames for that VLAN as tagged or untagged
on that port. The switch you refer to most likely has the
capability of maintaining such tables for only 256 VLANs.

Anoop
!