dscp club...

what is the first rule of dscp club...

no one talks about dscp club...

what is the second rule of dscp club...

no one talks about dscp club...

i give you... your map...




it is all there...

fact is you don't even have to look at it...

cs0 is zero

cs1 increments by 8

in each cs there are 3 af's and they begin with the class selector and increment by 1...

cs1 has af11 af12 and af13

cs3 is 3x8 and has 3 af's 31 32 and 33

but arteq you say, how can i possibly remember that af31 equals 26...

because it is 3x8 + 2...

class selector 4 is 4x8, 32...  it has 3 af's... each begin with 4 and increment by 1... af41 42 and 43....

cs4 is 32 so it's af's equal 34 36 38...

think of the class selectors as classful boundaries...

why does cs5 = 40... because 5x8=40...

it has an ef which is always equal to 46... this is voice, and voice breaks the pattern...

the ip precedence follows the cs...

the ip precedence for each af in cs 3 is 3... likewise for cs2, et al...

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSIntro.html

IP Routing

By default, Cisco IOS software (in accordance with RFC 791 and RFC 2474) marks  IGP traffic such as Routing Information Protocol (RIP/RIPv2), Open Shortest Path First (OSPF), and Enhanced Interior Gateway Routing Protocol (EIGRP) to DSCP CS6. However, Cisco IOS software also has an internal mechanism for granting internal priority to important control datagrams as they are processed within the router. This mechanism is called PAK_PRIORITY.

As datagrams are processed though the router and down to the interfaces, they are internally encapsulated with a small packet header, referred to as the PAKTYPE structure. Within the fields of this internal header there is a PAK_PRIORITY flag that indicates the relative importance of control packets to the internal processing systems of the router. PAK_PRIORITY designation is a critical internal Cisco IOS software operation and, as such, is not administratively configurable in any way.

Note that EGP traffic such as Border Gateway Protocol (BGP) traffic is marked by default to DSCP CS6 but does not receive such PAK_PRIORITY preferential treatment and may need to be explicitly protected in order to maintain peering sessions.

When addressing the QoS needs of IP Routing traffic, Cisco recommends the following guidelines:

•IP Routing traffic should be marked to DSCP CS6; this is default behavior on Cisco IOS platforms.

•IGPs are usually adequately protected with the Cisco IOS internal PAK_Priority mechanism; Cisco recommends that EGPs such as BGP have an explicit class for IP routing with a minimal bandwidth guarantee.

•Cisco IOS automatically marks IP Routing traffic to DSCP CS6.

Additional information on PAK_PRIORITY can be found at:
http://www.cisco.com/warp/public/105/rtgupdates.html