From: Donny MATEO (donny.mateo@sg.ca-indosuez.com)
Date: Wed Nov 13 2002 - 22:41:13 GMT-3
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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