802.1q vlans trunking
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Posted by julde on June 13, 2005, 5:09 am
Please log in for more thread options 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 | ||||||||||||||||
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Posted by Walter Roberson on June 13, 2005, 6:39 pm
Please log in for more thread options :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)? 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 | ||||||||||||||||
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Posted by anoop on June 13, 2005, 11:10 pm
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julde wrote: 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 | ||||||||||||||||
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> 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)?