I found the vlan in one end of isl trunk is not able to communicate with
the other end of the 802.1q trunk (say, GSR). Thus, I wonder whether it is
possible to use them at the same time and all cisco switches and routers
are able to communicate, ISL for most, but 802.1q for trunk with GSR.
Thanks. :)
Rgds,
Kenneth Cho
On Wed, 20 Sep 2000, 'Dmitri Kalintsev' wrote:
> On Wed, Sep 20, 2000 at 01:11:30PM +0200, Oleg Kostine wrote:
>
> > One little detail: If you use 802.1q on Cisco you have only one STP domain
> > for all vlans over the trunk. 29xx,35xx or 6x00 manuals is a good source
> > for more info.
>
> According to:
> http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_5_5/sw_cfg/spantree.htm
>
> "Spanning Tree and IEEE 802.1Q Trunks
>
> IEEE 802.1Q VLAN trunks impose some limitations on the spanning-tree strategy
> for a network. In a network of Cisco switches connected through 802.1Q
> trunks, the switches maintain one instance of spanning tree for each VLAN
> allowed on the trunks. However, non-Cisco 802.1Q switches maintain only one
> instance of spanning tree for all VLANs allowed on the trunks.
>
> When you connect a Cisco switch to a non-Cisco device through an 802.1Q
> trunk, the Cisco switch combines the spanning-tree instance of the 802.1Q
> native VLAN of the trunk with the spanning-tree instance of the non-Cisco
> 802.1Q switch. However, all per-VLAN spanning tree information is maintained
> by Cisco switches separated by a cloud of non-Cisco 802.1Q switches. The
> non-Cisco 802.1Q cloud separating the Cisco switches is treated as a single
> trunk link between the switches."
>
>
> Yes, in cat6k docs it does say though, that 802.1q will run only one STP.
> This makes me believe, that 6k is not a Cisco Switch (tm). :)
>
> [not 100% relevant info on]
>
> http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_5_5/cnfg_gd/vlans.htm :
>
> "Mapping 802.1Q VLANs to ISL VLANs
>
> The valid range of user-configured Inter-Switch Link (ISL) VLANs is 1-1000.
> The valid range of VLANs specified in the IEEE 802.1Q standard is 0-4095. In
> a network environment with non-Cisco devices connected to Cisco switches
> through 802.1Q trunks, you must map 802.1Q VLAN numbers greater than 1000 to
> ISL VLAN numbers.
>
> 802.1Q VLANs in the range 1-1000 are automatically mapped to the
> corresponding ISL VLAN. 802.1Q VLAN numbers greater than 1000 must be mapped
> to an ISL VLAN in order to be recognized and forwarded by Cisco switches."
>
> [not 100% relevant info off]
>
> [skip]
>
> P.S. Please tell me, how is this whole 802.1q/STP story bad for you? I don't
> get it, why I should care. Mind it, but not *care*. ;^)
>
> SY,
> --
> CCNP,CCDP (R&S) Dmitri E. Kalintsev
> CDPlayer@irc Chief of Network Operations @ Sonorous Networks
> dek @ hades.uz phone: +27 11-327-1524 fax: 327-7648
> http://hades.uz UIN:7150410 cell +27 82-336-1033
>
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