Switches with kludgey VLAN implementations?

Switches with kludgey VLAN implementations?

Post by Jeff Josli » Fri, 13 Jun 2003 14:30:01



Rich Seifert's "The Switch Book" describes a way for a switch to
implement VLANs: the forwarding table is the same as that for a
VLAN-unaware switch, but before forwarding a frame the switch checks
that the outgoing port is a member of the frame's VLAN. This seems to
me to be a kludge that allows a switch to have VLAN capability added
without changing the forwarding table implementation.

The Cisco switches that I have access to do things differently. I can
see the difference if I use the same MAC address in different VLANs.
The switches I have tested allow the same MAC address to map to
different ports on different VLANs.

For reasons I can't explain right now, the distinction is important to
me. The question is, how many switches out there implement VLANs in
the way described in Rich's book? I am interested both any currently
shipping switches do it that way, and what fraction of the installed
base of switches do it that way.

Jeff Joslin

 
 
 

Switches with kludgey VLAN implementations?

Post by Michele Bergonzon » Fri, 13 Jun 2003 17:15:22




Quote:> Rich Seifert's "The Switch Book" describes a way for a switch to
> implement VLANs: the forwarding table is the same as that for a
> VLAN-unaware switch, but before forwarding a frame the switch checks
> that the outgoing port is a member of the frame's VLAN.
...
> me. The question is, how many switches out there implement VLANs in
> the way described in Rich's book? I am interested both any currently
> shipping switches do it that way, and what fraction of the installed
> base of switches do it that way.

I know for sure that:

HP 25xx, 4000, 8000 implement the single forwarding database model.

3com 3300, 1100 implement the multiple forwarding database model.

Bye,
                 Bergonz

--
---
Ing. Michele Bergonzoni - Laboratori Fondazione Guglielmo Marconi
info and PGP key at http://www.labs.it/bergonz/
Phone:+39-051-6781926 Fax:+39-051-846479
Telecommunications consultants, Microwave systems & circuits development.

 
 
 

1. native vlan mismatch on 2 2924 switches w/ only 1 vlan defined (same on both switches)

i'm getting the following message logged every minute:

Jul  1 14:56:30: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch
discovered on FastEthernet0/2 (0), with switchs1-cc-cab4.jct.ac.il
FastEthernet0/23 (1).

ok, there's lots in this group written about vlan mismatches.
i haven't seen anything with all ports on both switches in the same
vlan!

both switches are 2924-xl's w/ all 24 ports on each unit in vlan1.
the unit which logs the messages is running Version 11.2(8.2)SA6.
the other unit is running Version 12.0(5)WC5.

everythings seems to be working fine though.
each switch has several production servers on it, so we would have
noticed if there were connectivity or performance effects.

any additional insight would be appreciated.
tnx
ams

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