From: Steve McNutt (lpd@xxxxxxxxxxxxxxxx)
Date: Tue Oct 03 2000 - 20:02:38 GMT-3
I know this is going to be a crappy explaination. token ring is a bith to
explain, and token ring switching is bitch*2 hehe.
In case you don't know this, there are two kind of frames in token ring.
MAC frames and LLC frames. MAC frames perform ring managment functions.
LLC frames carry user data. the Token Ring state machine makes extensive
use of MAC frames to do it's thing, and the amount of MAC traffic you have
increases with the number of hosts on the ring. A ring with 200 hosts has
quite a bit of mac broadcast traffic being generated, esp when people boot
up their machines in the morning.
now to the answers:
1. LLC broadcast frames are free the traverse the entire bridged domain
whereas MAC frames are not allowed to leave the ring (or switchport if your
a switch). It's possible to have LLC broadcast frames that are constrained
to a single TRCRF by the switch (using a functional group for multicast
comes to mind), but normally you don't see that kind of thing. Of course
you can have more LLC broadcast traffic than MAC broadcast traffic on a ring
at any given point in time. I was just trying to point out that multiple
TRCRFs on a TRBRF don't really buy you anything performance-wise because the
MAC traffic is constrained at the port level, and most LLC traffic traverses
ALL trcrf's in the trbrf VLAN.
2. with srt, LLC broadcasts will span all of your trcrf's. with srb at the
trcrf level, I do belive (although I've never tried it) that frames without
a RIF will not be forwarded to any other trcrfs. Honestly I don't think
this would be very good practice. Can't think of a good reason not to run
SRT on all of your token ring vlans. If you want to constrain LLC broadcast
traffic, use a router.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Jack Heney
Sent: Tuesday, October 03, 2000 5:40 PM
To: Steve.McNutt@ahlcorp.com; ccielab@groupstudy.com
Subject: RE: Token Ring Vlans
Okay...It's becoming clearer but I have 2 more questions....Why is the
majority of your ring level broadcast traffic MAC frames? Also, It says
that you can configure the 3900 for either SRB or SRT between the trcrf and
the trbrf...If I choose SRT for two trcrf's that share a parent trbrf, does
that mean that these broadcasts will span multiple trcrf's...For that
matter, if I choose SRB for both trcrf's, will that prevent the broadcasts
from being bridged from one trcrf to another through the trbrf?
Thanks again,
Jack
>From: "McNutt, Steve" <Steve.McNutt@ahlcorp.com>
>Reply-To: "McNutt, Steve" <Steve.McNutt@ahlcorp.com>
>To: "'ccielab@groupstudy.com'" <ccielab@groupstudy.com>
>Subject: RE: Token Ring Vlans
>Date: Tue, 3 Oct 2000 15:48:22 -0400
>
>Hey, that was a pretty good explanation.. except for the Cisco
>markettecture
>about the usefulness of TRCRFs. ;-)
>
>In reality, MAC frames (which are comprise the bulk of your ring level
>broadcast traffic) do not span the TRCRF or even enter the backplane of the
>switch (switchports in the same trcrf are transparently bridged). the
>microsegmentation effect occurs regardless of whether two switchports are
>on
>the same or different trcrfs.
>
>My experience has been that you use multiple TRCRFs because TRCRFs cannot
>span switches(with the execption of the default trcrf), whereas TRBRFs can.
>So if you have multiple switches that you want to be on the same ip subnet,
>you need to create a TRCRF for each switch and then assign it to the same
>parent TRBRF.
>
>
>-----Original Message-----
>From: Asbjorn Hojmark [mailto:Asbjorn@Hojmark.ORG]
>Sent: Tuesday, October 03, 2000 2:57 PM
>To: 'Jack Heney'
>Cc: ccielab@groupstudy.com
>Subject: RE: Token Ring Vlans
>
> > If so, what advantage is gained by creating these vlans?
>
>It's like micro-segmentation for token-ring. Remember that
>stations on a ring share a token and that some frames are
>local to a ring while others are global for the bridged
>domain.
>
> > Also, can rings that don't share the same parent trbrf
> > communicate without some sort of routing occurring
>
>No.
>
>HTH,
>-A
>--
>Heroes: Vint Cerf & Bob Kahn, Leonard Kleinrock, Robert Metcalfe
>Links : http://www.hojmark.org/networking/
>
>
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