From: inaki.blanco-acosta@bt.com
Date: Thu Nov 14 2002 - 13:38:29 GMT-3
As well as other reasons like restrictions inherent to ISL, e.g. ports that
can be bundled,
or issues associated to the hashing algorithm it uses for load balancing...
although the
implementation of dot1q needs to be refined, the specification is more
flexible
rgds,
i.
-----Original Message-----
From: Chuck Church [mailto:cchurch@optonline.net]
Sent: Thursday, November 14, 2002 16:08
To: Donny MATEO; Hedi Abdelkafi
Cc: GroupStudy (E-mail)
Subject: Re: ISL and Dot1q Trunk
Hedi,
I think the fact that Cisco themselves is moving away from ISL is reason
enough to use just dot1Q. Currently, the 4000 series doesn't support ISL,
nor does the 2950s. They might have all ISL-capable equipment now, but what
about when they go to buy a new 3550-sized switch in a couple years? I
doubt ISL would be an option on that. Or if the company merges with another
that's all Cat4000? Seems like there's a lot of reasons to use dot1Q, but
no compelling ones for ISL. Although I think the 3920 TR switch only
supported ISL :)...
Chuck Church
CCIE #8776, MCNE, MCSE
----- Original Message -----
From: "Donny MATEO" <donny.mateo@sg.ca-indosuez.com>
To: "Hedi Abdelkafi" <Hedi.Abdelk@simac.lu>
Cc: "GroupStudy (E-mail)" <ccielab@groupstudy.com>
Sent: Wednesday, November 13, 2002 8:41 PM
Subject: RE: ISL and Dot1q Trunk
> I was under the impression that both ISL and dot1Q support COS on the L2
data frame.
> As for ISL it would be 3 of the least significant bits of the 1 byte user
field and Dot1Q would be
> 3 of the most significant bit of the tag control information field.
> Also I read the documentation of 3550 that actually supports both. you
simply need to enable the mls
> qos on the switch and then set the interface to trust the COS value of the
frame (after which you
> need to specify the mapping of the COS to internal DSCP but that's another
story).
>
> I don't see how you gonna convince a customer with that.
> I would only say that dot1q is an open standard. It can be interoperable
with everything else in the
> market (supposedbly), so it's a more scalable choice bla bla
bla........... (network design stuff)
>
> Donny
>
>
>
> "Hedi Abdelkafi"
> <Hedi.Abdelk@sima To: "Larson, Chris"
<CLarson@usaid.gov>, "GroupStudy (E-mail)"
> c.lu> <ccielab@groupstudy.com>
> Sent by: cc:
> nobody@groupstudy Subject: RE: ISL and Dot1q
Trunk
> .com
>
>
> 13-11-2002 23:25
> Please respond to
> "Hedi Abdelkafi"
>
>
>
>
>
>
> Hi,
>
> You give me a very good idea to switch off ISL from the network : QoS.
> In fact, the customer wants to implement QoS on the network.
>
> ISL also contains a priority fields in the header but it's only a four-bit
> code.
> And I don't know if the mapping between L2 and L3 can be easily done than
with
> Dot1q.
>
> You put me on the way to follow...
>
> Thanks a lot for your help.
>
> Bye
>
> -----Original Message-----
> From: Larson, Chris [mailto:CLarson@usaid.gov]
> Sent: mercredi 13 novembre 2002 15:24
> To: Hedi Abdelkafi
> Subject: RE: ISL and Dot1q Trunk
>
>
>
> Why would they want to use both? Is there a need or reason?
>
> 1)ISL is proprietary
> 2) It adds data to the pcket header causing packets using ISL to show up
as
> Giants (error) in many network management systems. Inlcuding U believe the
> routers themselves when doing a show int.
>
> 3) Dot1q is not proprietary and is standard therefore it is likely that
any
> mixing of equipment outside of Cisco devices will require the use of
Dot1q
> and ISL would likely not be supported.
>
> 4) I am not 100% on this but........... 802.1q incorporates 802.1p
allowing
> QoS to be mapped from leyer 2 to 3 and vice versa. Important to do when
you
> may have trunks carrying voice, video or other sensitive info.
>
> If I can think of any others I will forward them.
>
>
>
> -----Original Message-----
> From: Hedi Abdelkafi [SMTP:Hedi.Abdelk@simac.lu]
> Sent: Wednesday, November 13, 2002 4:54 AM
> To: GroupStudy (E-mail)
> Subject: ISL and Dot1q Trunk
>
> Hi,
>
> I have to setup a new network with Cat6k (with 10 Ge interface) and
Cat3550.
> ISL encapsulation is not supported on 10 GE interface so we have to use
Dot1Q
> encapsualtion on that kind of link.
>
> The customer wants to use both encapsulation mode (ISL on Gigabit and
Dot1q
> on 10 GE).
> I prefer to use only Dot1Q accross the whole network.
>
> What argument can I give in order so setup this new network with only one
> encapsulation method ?
> Does someone have a bad experience when mixing both ?
>
> PS : I have already said to the customer that some device (Cat2950 if I'm
> wrong) support only Dot1q. He told me that the only device that will be
used
> are cat 3550 !
>
> Any idea or documentation is welcome !
>
> Thanks for your help.
>
> Bye
>
>
>
>
>
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