Thanks a lot for your input.
Priscilla Oppenheimer wrote:
> Where are the servers or mainframes that the Token Ring PCs are using? Do
> they support a large frame size? What is the traffic flow? Does the traffic
> from the PCs travel across an Ethernet segment or some other segment that
> does not support a large frame size? Are you using bridging or routing?
>
> The steps you should take include:
>
> Analyze the physical topology.
> Analyze the logical topology and traffic flow.
> Define the problem with as much detail as possible. How else can you
> characterize the "poor network performance?"
> Gather facts, such as why was the frame size changed? Does it affect all
> users? Is it reproducible across applications? What is the actual response
> time? What are the error rates at the data-link layer, upper layers?
> Analyze router configurations, determine if bridging or routing is
> happening. What do show interface commands show?
> Consider possibilities. Try to do this without bias and assumptions (such
> as the assumption that performance problems are caused by frame size)
> Create an action plan
> Implement the action plan
> Observe the results
>
> If you have really done the initial steps and are ready to implement the
> action plan of changing frame size, you are doing the right think to think
> about the implications of making this change.
>
> With very little data to go on, I think you can make the change without
> much risk. Both routing and bridging supposedly handle various frame sizes.
>
> Priscilla
>
> At 04:38 PM 9/4/01, khramov wrote:
> >Here is what I've got:
> >We have a remote site where we run token ring and ethernet. Core router
> >(Cisco 4500)
> >has 1 tr interface and 2 ethernet interfaces. One ethernet interface goes
> >out to the
> >firewall and the other interface is just an ethernet subnet with
> >workstations.
> >Some time in the past, I am not sure but for whatever reason frame size on
> >token ring
> >interface was changed to 1500 from I believe the default 4500. Ever since
> >users have
> >been complaining about poor network performance. I think that if change
MTU
> >it might
> >speed them up a little bit. However, all the PC are also set to 1500
frame
> >size. So I
> >am debating whether changing the frame size will help users and if I
change
> >it how long
> >the network will be down or is it just a matter of rebooting PCs.
> >So I guess my router does both routing and translation. What do you
think I
> >should do?
> >
> >Priscilla Oppenheimer wrote:
> >
> > > At 02:40 PM 9/4/01, khramov wrote:
> > > >I need to change frame size on of my Token Ring subnets. If I change
the
> > > >Token Ring frame size on the router and it will be different (larger)
> > > >than the frame size that is configured on a work station how is it
going
> > > >to affect the work station? And if I change the frame size on the
> > > >workstation first would that crash the router?
> > > >Thanks
> > >
> > > It shouldn't be a serious problem either way you do it. Users may have
to
> > > re-establish connections, however.
> > >
> > > Are the routers truly routers or are they source-routing bridges? With
> > > source-route bridging, each bridge checks the "largest frame" field and
> > > decrements it if the bridge is configured for something smaller than is
> in
> > > the frame. This happens during route discovery and session
establishment.
> > > Changing one of the bridges after sessions are established could cause
> > > problems.
> > >
> > > If the routers are truly routers and are routing IP, there's a similar
> > > situation. IP hosts can use IP maximum transmission unit (MTU)
discovery
> to
> > > determine the largest possible frame size to use. This happens during
> > > session establishment. Changing the MTU on one of the routers after
> > > sessions are established could cause problems.
> > >
> > > But routers shouldn't crash and there shouldn't be any other dire
> > > consequences. Also, it sounds like you are increasing MTU which is less
> > > worrisome than decreasing MTU.
> > >
> > > Do you do any translational bridging between Ethernet and Token Ring
> > > segments? Translational bridging can be difficult to get working,
> > > especially if you use Token Ring frame sizes that are larger than
> Ethernet
> > > allows (1500 bytes). If you use routing instead of bridging, there will
> be
> > > fewer problems.
> > >
> > > If your routers are now going to need to fragment and reassemble IP
> > > packets, in order to go between Token Ring which supports larger frames
> and
> > > Ethernet which supports 1500 byte frames, keep in mind that the routers
> > > will be slower. This is additional work that they don't normally have
to
> > > do. I think it forces them to use process switching instead of the
faster
> > > switching methods.
> > >
> > > Priscilla
> > > ________________________
> > >
> > > Priscilla Oppenheimer
> > > http://www.priscilla.com
> ________________________
>
> Priscilla Oppenheimer
> http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=18487&t=18466
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