Classification and Marking Part 2
- IP Precedence – Old Way
- Diffserv Codepoint/DSCP – New Way
Where Should I Mark?
Mark the traffic as close to the source as you possibly can. Cisco refer to as the ‘trust boundary’. Marking will be trusted via the entire network.
Types of Marking
- Typically stripped at router hops
- CoS – 8 Bits
- Frame Relay DE Bit
- ATM CLP Bit
- MPLS EXP Bits
- Passed through routers
- IP Precedence
- True end to end QoS
How To Mark
(At Trust Boundary of 1st Router)
1. Create a class map IP_PHONE_AUDIO to match protocol RTP. (Class)
2. Create a policy map called MARK_VOICE, class IP_PHONE_AUDIO, set ip precedence (0-7 value) (5 = critical for voice)
show policy-map to verify
3. Apply policy map to interface (incoming interface from source)
service-policy input MARK_VOICE
This is a complete marking configuration to mark voice as critical.
Marking Values – CoS and IP Precedence
7-Reserved (Routing Protocols, Management Traffic etc… Important for network to be working that voice traffic!)
5-Voice Bearer – (1st value we can use)
3-Call Signalling (RTCP – Call Stats, SIP, SCCP etc…)
2-High Priority Data – Citrix, SNA
1-Medium Priority Data – SQL
0-Best Effort – P2P/HTTP
Now is a packet marked? Details…
IP Precedence – Layer 3 = ToS
CoS – Layer 2 (3 bits only 0-7)
ToS = 1 Byte/8 Bits
IP Precedence marks using 0-7 and only uses 1st 3 bits of packet (4, 2, 1)
DSCP uses all 8 bits, still backwards compatible with IP Precedence.
8 Bits into 3 groups: (Left to right)
- 3 bits – Major Group
- 3 bits – Minor Group
- 2 bits – ECN – Explicit Congestion Notification
set dscp ? (0-63 values)
As only 6 bits are used, we are never going to total more than 64 in binary.
128 64 32 16 8 4 2 1 BOLD = 64
0-7 (3 bits) (Allows backward compatibility with IP Precedence)
Minor Class/Drop Preference
LOWER = BEST/HIGHER DROP PREFERENCE
- Default = 0
- AF1 (Assured Forwarding) – IP Precedence 1 – AF11, AF12 and AF13
- AF2 – IP Precedence 2 – AF21, AF22, and AF23
- AF3 – IP Precedence 3 – AF31, AF32 and AF33
- AF4 – IP Precedence 4 – AF41, AF42 and AF43
- EF (Expedited Forwarding/Ultimate QoS) – IP Precedence 5 (No drop pref)
- Major Class = Left Hand Number
- Minor Class = Right Hand Number
- 2 sets of 3 bits each!
Use DSCP and same flexibility as IP Precedence. No drop classes with other 3 bits.