From: Scott Morris (swm@emanon.com)
Date: Mon Jul 14 2003 - 17:33:11 GMT-3
While I don't have the IPE material to compare things to, are you sure
there wasn't any other QoS requirement someplace to make that a required
part of the solution? It seems odd that one side is changed to 1 and
the other is not.
For comparisons.... CoS is a 3-bit field in the ethernet header. ToS
is a 1 byte field in the IP header. IP-Prec is 3 bits of that field
while DSCP is 6 bits of the same ToS field.
Oftentimes, CoS and IP-Prec are used equally (both are 3 bits). With
DSCP, things get a little hairier, but there is overlap between them...
ToS = 1 2 3 4 5 6 7 8 bits
Prec = 1 2 3 - - - - - bits
DSCP = 1 2 3 4 5 6 - - bits
All the same bits.
So a value of IP Prec 1 = 001 (IP Prec) = 001000 (8) in DSCP speak
IP prec 2 = 16 DSCP
3 = 24, 4 = 32, 5 = 40, 6 = 48, 7 = 56
You can create your own maps of what equals what between DSCP and CoS
with the 'mls qos map' command set. Check out:
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/1214ea1/3550cr
/cli1.htm#70462
HTH,
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Jason Cash
Sent: Monday, July 14, 2003 4:15 PM
To: ccielab@groupstudy.com
Subject: 3550 Config - vocie Vlan, mls qos. etc.
I am working on IPE Section 36 and the Advanced 3550 section instructs:
IP Phone - 1 will be on VLAN 101 & connecting device to IP Phone will be
on VLAN
102. IP Phone will be using 802.1Q encapsulation.
IP Phone - 2 will be on VLAN201 & connecting device to IP Phone will be
on
VLAN202. FastEthernet0/12 will be statically configured to 802.1Q
trunking mode
for IP Phone-2 connectivity.
The solution is provided as such:
interface FastEthernet0/11
switchport access vlan 102
switchport voice vlan 101
switchport trunk encapsulation dot1q
switchport priority extend cos 0
no ip address
mls qos cos 1
mls qos cos override
spanning-tree portfast
!
interface FastEthernet0/12
switchport trunk encapsulation dot1q
switchport trunk native vlan 202
switchport mode trunk
switchport voice vlan 201
no ip address
spanning-tree portfast
I understand the commands entered now, but that still does not explain
how the values were arrive at. In particular the '1' in 'mls qos cos
1'. I take this to be that the CoS value is set to 1 on all incoming
packet to the interface, but why 1? Can someone provide me with a ToS/
CoS/DSCP chart?
Also, it seems that the same instruction is given for IP Phone 2, but
the config is not identical. Any explanations are appreciated
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